Impact of ghrelin on islet size in non-pregnant and pregnant female mice

Reducing ghrelin by ghrelin gene knockout (GKO), ghrelin-cell ablation, or high-fat diet feeding increases islet size and β-cell mass in male mice. Here, we determined if reducing ghrelin also enlarges islets in females, and if pregnancy-associated changes in islet size are related to reduced ghrelin. Islet size and β-cell mass were larger (P=0.057 for β-cell mass) in female GKO mice. Pregnancy was associated with reduced ghrelin and increased LEAP2 [a ghrelin receptor (GHSR) antagonist] in WT mice. Ghrelin deletion and pregnancy each increased islet size (by ∼19.9-30.2% and ∼34.9-46.4%, respectively), percentage of large islets (>25 µm2 x 103, by ∼21.8-42% and ∼21.2-41.2%, respectively) and β-cell mass (by ∼15.7-23.8% and ∼65.2-76.8%, respectively). Neither islet cross-sectional area, β-cell cross-sectional area, nor β-cell mass correlated with plasma ghrelin, although all positively correlated with LEAP2 (P=0.081 for islet cross-sectional area). In ad lib-fed mice, there was an effect of pregnancy, but not ghrelin deletion, to change (raise) plasma insulin without impacting blood glucose. Similarly, there was an effect of pregnancy, but not ghrelin deletion, to change (lower) blood glucose area under the curve during a glucose tolerance test. Thus, genetic deletion of ghrelin increases islet size and β-cell cross-sectional area in female mice, similar to males. Yet, despite pregnancy-associated reductions in ghrelin, other factors appear to govern islet enlargement and changes to insulin sensitivity and glucose tolerance in the setting of pregnancy. In the case of islet size and β-cell mass, one of those factors may be the pregnancy-associated increase in LEAP2.

Ghrelin-responsive mediobasal hypothalamic neurons mediate exercise-associated food intake and exercise endurance

Previous studies have implicated the orexigenic hormone ghrelin as a mediator of exercise endurance and the feeding response postexercise. Specifically, plasma ghrelin levels nearly double in mice when they are subjected to an hour-long bout of high-intensity interval exercise (HIIE) using treadmills. Also, growth hormone secretagogue receptor-null (GHSR-null) mice exhibit decreased food intake following HIIE and diminished running distance (time until exhaustion) during a longer, stepwise exercise endurance protocol. To investigate whether ghrelin-responsive mediobasal hypothalamus (MBH) neurons mediate these effects, we stereotaxically delivered the inhibitory designer receptor exclusively activated by designer drugs virus AAV2-hSyn-DIO-hM4(Gi)-mCherry to the MBH of Ghsr-IRES-Cre mice, which express Cre recombinase directed by the Ghsr promoter. We found that chemogenetic inhibition of GHSR-expressing MBH neurons (upon delivery of clozapine-N-oxide) 1) suppressed food intake following HIIE, 2) reduced maximum running distance and raised blood glucose and blood lactate levels during an exercise endurance protocol, 3) reduced food intake following ghrelin administration, and 4) did not affect glucose tolerance. Further, HIIE increased MBH Ghsr expression. These results indicate that activation of ghrelin-responsive MBH neurons is required for the normal feeding response to HIIE and the usual amount of running exhibited during an exercise endurance protocol.

Ghrelin deletion and conditional ghrelin cell ablation increase pancreatic islet size in mice

Ghrelin exerts key effects on islet hormone secretion to regulate blood glucose levels. Here, we sought to determine whether ghrelin's effects on islets extend to the alteration of islet size and β cell mass. We demonstrate that reducing ghrelin - by ghrelin gene knockout (GKO), conditional ghrelin cell ablation, or high-fat diet (HFD) feeding - was associated with increased mean islet size (up to 62%), percentage of large islets (up to 854%), and β cell cross-sectional area (up to 51%). In GKO mice, these effects were more apparent in 10- to 12-week-old mice than in 4-week-old mice. Higher β cell numbers from decreased β cell apoptosis drove the increase in β cell cross-sectional area. Conditional ghrelin cell ablation in adult mice increased the β cell number per islet by 40% within 4 weeks. A negative correlation between islet size and plasma ghrelin in HFD-fed plus chow-fed WT mice, together with even larger islet sizes in HFD-fed GKO mice than in HFD-fed WT mice, suggests that reduced ghrelin was not solely responsible for diet-induced obesity-associated islet enlargement. Single-cell transcriptomics revealed changes in gene expression in several GKO islet cell types, including upregulation of Manf, Dnajc3, and Gnas expression in β cells, which supports decreased β cell apoptosis and/or increased β cell proliferation. These effects of ghrelin reduction on islet morphology might prove useful when designing new therapies for diabetes.

Ghrelin does not impact the blunted counterregulatory response to recurrent hypoglycemia in mice

Introduction

Recurrent episodes of insulin-induced hypoglycemia in patients with diabetes mellitus can result in hypoglycemia-associated autonomic failure (HAAF), which is characterized by a compromised response to hypoglycemia by counterregulatory hormones (counterregulatory response; CRR) and hypoglycemia unawareness. HAAF is a leading cause of morbidity in diabetes and often hinders optimal regulation of blood glucose levels. Yet, the molecular pathways underlying HAAF remain incompletely described. We previously reported that in mice, ghrelin is permissive for the usual CRR to insulin-induced hypoglycemia. Here, we tested the hypothesis that attenuated release of ghrelin both results from HAAF and contributes to HAAF.

Methods

C57BL/6N mice, ghrelin-knockout (KO) + control mice, and GhIRKO (ghrelin cell-selective insulin receptor knockout) + control mice were randomized to one of three treatment groups: a "Euglycemia" group was injected with saline and remained euglycemic; a 1X hypoglycemia ("1X Hypo") group underwent a single episode of insulin-induced hypoglycemia; a recurrent hypoglycemia ("Recurrent Hypo") group underwent repeated episodes of insulin-induced hypoglycemia over five successive days.

Results

Recurrent hypoglycemia exaggerated the reduction in blood glucose (by ~30%) and attenuated the elevations in plasma levels of the CRR hormones glucagon (by 64.5%) and epinephrine (by 52.9%) in C57BL/6N mice compared to a single hypoglycemic episode. Yet, plasma ghrelin was equivalently reduced in "1X Hypo" and "Recurrent Hypo" C57BL/6N mice. Ghrelin-KO mice exhibited neither exaggerated hypoglycemia in response to recurrent hypoglycemia, nor any additional attenuation in CRR hormone levels compared to wild-type littermates. Also, in response to recurrent hypoglycemia, GhIRKO mice exhibited nearly identical blood glucose and plasma CRR hormone levels as littermates with intact insulin receptor expression (floxed-IR mice), despite higher plasma ghrelin in GhIRKO mice.

Conclusions

These data suggest that the usual reduction of plasma ghrelin due to insulin-induced hypoglycemia is unaltered by recurrent hypoglycemia and that ghrelin does not impact blood glucose or the blunted CRR hormone responses during recurrent hypoglycemia.

Effects of thermoneutrality on food intake, body weight, and body composition in a Prader-Willi syndrome mouse model

OBJECTIVE

Prader-Willi syndrome (PWS) is a multisystem genetic disorder. Unfortunately, none of several mouse models carrying PWS mutations emulates the entirety of the human PWS phenotype, including hyperphagia plus obesity.

METHODS

To determine whether housing at thermoneutrality (TN, 30 °C) permits the development of hyperphagia and obesity in the Snord116del PWS mouse model, the effects of housing three different ages of Snord116del and wild-type (WT) littermates at TN versus room temperature (RT, 22-24 °C) for 8 weeks were compared.

RESULTS

Snord116del mice born and maintained at TN exhibited lower body weight curves, lower percentage fat mass, and lower food intake than WT mice at RT. In 4- to 6-month-old high-fat diet-fed female mice, TN raised the Snord116del body weight curve closer to that of RT-housed WT mice although the TN-housed Snord116del mice did not gain more adiposity or exhibit greater food intake. In 6- to 8-month-old high-fat diet-fed male mice, body weight, adiposity, and food intake of TN-housed Snord116del mice remained far below levels in RT-housed WT mice. TN elicited hypotonia in Snord116del adults and exacerbated mortality of Snord116del newborns.

CONCLUSIONS

In none of three tested TN protocols were greater food intake, body weight, or adiposity induced in Snord116del mice compared with RT-housed WT mice.

High Coexpression of the Ghrelin and LEAP2 Receptor GHSR With Pancreatic Polypeptide in Mouse and Human Islets

Islets represent an important site of direct action of the hormone ghrelin, with expression of the ghrelin receptor (growth hormone secretagogue receptor; GHSR) having been localized variably to alpha cells, beta cells, and/or somatostatin (SST)-secreting delta cells. To our knowledge, GHSR expression by pancreatic polypeptide (PP)-expressing gamma cells has not been specifically investigated. Here, histochemical analyses of Ghsr-IRES-Cre × Cre-dependent ROSA26-yellow fluorescent protein (YFP) reporter mice showed 85% of GHSR-expressing islet cells coexpress PP, 50% coexpress SST, and 47% coexpress PP + SST. Analysis of single-cell transcriptomic data from mouse pancreas revealed 95% of Ghsr-expressing cells coexpress Ppy, 100% coexpress Sst, and 95% coexpress Ppy + Sst. This expression was restricted to gamma-cell and delta-cell clusters. Analysis of several single-cell human pancreatic transcriptome data sets revealed 59% of GHSR-expressing cells coexpress PPY, 95% coexpress SST, and 57% coexpress PPY + SST. This expression was prominent in delta-cell and beta-cell clusters, also occurring in other clusters including gamma cells and alpha cells. GHSR expression levels were upregulated by type 2 diabetes mellitus in beta cells. In mice, plasma PP positively correlated with fat mass and with plasma levels of the endogenous GHSR antagonist/inverse agonist LEAP2. Plasma PP also elevated on LEAP2 and synthetic GHSR antagonist administration. These data suggest that in addition to delta cells, beta cells, and alpha cells, PP-expressing pancreatic cells likely represent important direct targets for LEAP2 and/or ghrelin both in mice and humans.

Ghrelin cell-expressed insulin receptors mediate meal- and obesity-induced declines in plasma ghrelin

Mechanisms underlying postprandial and obesity-associated plasma ghrelin reductions are incompletely understood. Here, using ghrelin cell-selective insulin receptor-KO (GhIRKO) mice, we tested the impact of insulin, acting via ghrelin cell-expressed insulin receptors (IRs), to suppress ghrelin secretion. Insulin reduced ghrelin secretion from cultured gastric mucosal cells of control mice but not from those of GhIRKO mice. Acute insulin challenge and insulin infusion during both hyperinsulinemic-hypoglycemic clamps and hyperinsulinemic-euglycemic clamps lowered plasma ghrelin in control mice but not GhIRKO mice. Thus, ghrelin cell-expressed IRs are required for insulin-mediated reductions in plasma ghrelin. Furthermore, interventions that naturally raise insulin (glucose gavage, refeeding following fasting, and chronic high-fat diet) also lowered plasma ghrelin only in control mice - not GhIRKO mice. Thus, meal- and obesity-associated increases in insulin, acting via ghrelin cell-expressed IRs, represent a major, direct negative modulator of ghrelin secretion in vivo, as opposed to ingested or metabolized macronutrients. Refed GhIRKO mice exhibited reduced plasma insulin, highlighting ghrelin's actions to inhibit insulin release via a feedback loop. Moreover, GhIRKO mice required reduced glucose infusion rates during hyperinsulinemic-hypoglycemic clamps, suggesting that suppressed ghrelin release resulting from direct insulin action on ghrelin cells usually limits ghrelin's full potential to protect against insulin-induced hypoglycemia.

LEAP2 deletion in mice enhances ghrelin's actions as an orexigen and growth hormone secretagogue

Objective

The hormone liver-expressed antimicrobial peptide-2 (LEAP2) is a recently identified antagonist and an inverse agonist of the growth hormone secretagogue receptor (GHSR). GHSR's other well-known endogenous ligand, acyl-ghrelin, increases food intake, body weight, and GH secretion and is lowered in obesity but elevated upon fasting. In contrast, LEAP2 reduces acyl-ghrelin-induced food intake and GH secretion and is found elevated in obesity but lowered upon fasting. Thus, the plasma LEAP2/acyl-ghrelin molar ratio could be a key determinant modulating GHSR signaling in response to changes in body mass and feeding status. In particular, LEAP2 may serve to dampen acyl-ghrelin action in the setting of obesity, which is associated with ghrelin resistance. Here, we sought to determine the metabolic effects of genetic LEAP2 deletion.

Methods

We generated the first known LEAP2-KO mouse line. Food intake, GH secretion, and cellular activation (c-fos induction) in different brain regions following s.c. acyl-ghrelin administration in LEAP2-KO mice and wild-type littermates were determined. LEAP2-KO mice and wild-type littermates were submitted to a battery of tests (such as measurements of body weight, food intake, and body composition; indirect calorimetry, determination of locomotor activity, and meal patterning while housed in metabolic cages) over the course of 16 weeks of high-fat diet and/or standard chow feeding. Fat accumulation was assessed in hematoxylin & eosin-stained and oil red O-stained liver sections from these mice.

Results

LEAP2-KO mice were more sensitive to s.c. ghrelin. In particular, acyl-ghrelin acutely stimulated food intake at a dose of 0.5 mg/kg BW in standard chow-fed LEAP2-KO mice while a 2× higher dose was required by wild-type littermates. Also, acyl-ghrelin stimulated food intake at a dose of 1 mg/kg BW in high-fat diet-fed LEAP2-KO mice while not even a 10× higher dose was effective in wild-type littermates. Acyl-ghrelin induced a 90.9% higher plasma GH level and 77.2–119.7% higher numbers of c-fos-immunoreactive cells in the arcuate nucleus and olfactory bulb, respectively, in LEAP2-KO mice than in wild-type littermates. LEAP2 deletion raised body weight (by 15.0%), food intake (by 18.4%), lean mass (by 6.1%), hepatic fat (by 42.1%), and body length (by 1.7%) in females on long-term high-fat diet as compared to wild-type littermates. After only 4 weeks on the high-fat diet, female LEAP2-KO mice exhibited lower O₂ consumption (by 13%), heat production (by 9.5%), and locomotor activity (by 49%) than by wild-type littermates during the first part of the dark period. These genotype-dependent differences were not observed in high-fat diet-exposed males or female and male mice exposed for long term to standard chow diet.

Conclusions

LEAP2 deletion sensitizes lean and obese mice to the acute effects of administered acyl-ghrelin on food intake and GH secretion. LEAP2 deletion increases body weight in females chronically fed a high-fat diet as a result of lowered energy expenditure, reduced locomotor activity, and increased food intake. Furthermore, in female mice, LEAP2 deletion increases body length and exaggerates the hepatic fat accumulation normally associated with chronic high-fat diet feeding.

•

A novel line of LEAP2-knockout mice was generated.

•

LEAP2 deletion sensitizes mice to the GH secretory effects of administered ghrelin.

•

LEAP2 deletion reduces ghrelin resistance in diet-induced obese mice.

•

HFD-fed female LEAP2-KO mice eat more and gain more body weight and hepatic fat.

•

HFD-fed female LEAP2-KO mice exhibit lowered energy expenditure and activity.

Disrupting the ghrelin-growth hormone axis limits ghrelin's orexigenic but not glucoregulatory actions

Objective

Acyl-ghrelin regulates eating, body weight, blood glucose, and GH secretion upon binding to its receptor GHSR (growth hormone secretagogue receptor; ghrelin receptor). GHSR is distributed in several brain regions and some peripheral cell-types including pituitary somatotrophs. The objective of the current study was to determine the functional significance of acyl-ghrelin's action on GHSR-expressing somatotrophs in mediating GH secretion and several of acyl-ghrelin's metabolic actions.

Methods

GH-IRES-Cre mice and loxP-flanked (floxed) GHSR mice were newly developed and then crossed to one another to generate mice that lacked GHSR selectively from somatotrophs. Following validation of mice with somatotroph-selective GHSR deletion, metabolic responses of these mice and control littermates were assessed following both acute and chronic acyl-ghrelin administration, a 24-h fast, and a prolonged 60% chronic caloric restriction protocol modeling starvation.

Results

In mice with somatotroph-selective GHSR deletion, a single peripheral injection of acyl-ghrelin failed to induce GH secretion or increase food intake, unlike wild-type and other littermate control groups. However, the usual acute blood glucose increase in response to the acyl-ghrelin bolus was preserved. Similarly, chronic s.c. acyl-ghrelin administration to mice with somatotroph-selective GHSR deletion failed to increase plasma GH, food intake, or body weight. Physiologically elevating plasma acyl-ghrelin via a 24-h fast also failed to raise plasma GH and resulted in a limited hyperphagic response upon food reintroduction in mice with somatotroph-selective GHSR deletion, although those mice nonetheless did not exhibit an exaggerated reduction in blood glucose. Physiologically elevating plasma acyl-ghrelin via a 15-day caloric restriction protocol which provided only 40% of usual daily calories failed to raise plasma GH in mice with somatotroph-selective GHSR deletion, although those mice did not exhibit life-threatening hypoglycemia.

Conclusions

These results reveal that direct engagement of GHSR-expressing somatotrophs is required for a peripheral ghrelin bolus to acutely stimulate GH secretion and the actions of chronic acyl-ghrelin delivery and physiological plasma acyl-ghrelin elevations to increase plasma GH. These results also suggest that actions of acyl-ghrelin to increase food intake and body weight are reliant on direct activation of GHSRs expressed on somatotrophs. Furthermore, these results suggest that the glucoregulatory actions of acyl-ghrelin – in particular, its actions to raise blood glucose when acutely administered, prevent small blood glucose drops following a 24-h fast, and avert life-threatening hypoglycemia during an acute-on-chronic caloric restriction protocol – do not depend on GHSR expression by somatotrophs.

•

Mice with pituitary somatotroph-selective GHSR deletion were generated.

•

Somatotroph-expressed GHSRs mediate GH secretion and food intake after acute ghrelin.

•

Body weight effects of chronic ghrelin infusion require somatotroph-expressed GHSRs.

•

Somatotroph-expressed GHSRs enable GH to increase upon chronic caloric restriction.

•

Mice lacking somatotroph GHSRs maintain euglycemia upon chronic caloric restriction.

Role of Growth Hormone in Ghrelin’s Metabolic Actions

Objective: Ghrelin regulates eating, body weight, and blood glucose. Upon binding to its receptor (growth hormone secretagogue receptor; GHSR), administered ghrelin increases food intake, body weight, and blood glucose. In contrast, blocking ghrelin lowers body weight and food intake. Also, mice that lack ghrelin or GHSR develop life-threatening hypoglycemia when submitted to a prolonged caloric restriction protocol providing only 40% of usual daily calories. Although GHSR was first identified in the pituitary, ghrelin was first defined by its ability to stimulate GH secretion via GHSRs, GH replacement prevents hypoglycemia in ghrelin-KO mice undergoing prolonged caloric restriction, and GH is known to modulate body composition, relatively little attention has been devoted to the role of GH-secreting pituitary somatotrophs (“GH cells”) in ghrelin action. The objective here was to determine the requirement for GHSR-expressing GH cells in mediating ghrelin’s metabolic actions. Methods: Mice with GH cell-selective GHSR deletion were generated by crossing novel GH-IRES-Cre mice to novel floxed-GHSR mice. GH cell-selective GHSR knockout mice and three control littermate groups were studied. Plasma GH, food intake, and blood glucose were measured after ip or sc ghrelin administration. Blood glucose and plasma GH were measured over the course of a 15-d calorie restriction protocol providing only 40% of usual daily calories. Results: In mice with GH cell-selective GHSR deletion, ghrelin-induced GH secretion and food intake were attenuated (by 84.1% at 15 min and by 35.3% at 45 min, respectively) as compared to controls; ghrelin-induced blood glucose elevation was unchanged. Mice with GH cell-selective GHSR deletion exhibited an attenuated GH rise (by 76.8%) over the 15-d calorie restriction period, yet they nonetheless resisted life-threatening hypoglycemia which is observed in similarly-treated ghrelin-KO mice, GHSR-null mice, and mice with hepatocyte-selective GH receptor deletion. Conclusions: These results suggest that GH cell-expressed GHSRs are required for ghrelin’s acute orexigenic and GH secretory actions but are dispensable for ghrelin’s glucoregulatory actions, at least in the settings assessed here. Although GH cell-expressed GHSRs are required for the progressive GH elevations associated with prolonged calorie restriction, they are not required for ghrelin’s overall protective effects to block prolonged calorie restriction-associated hypoglycemia.

Lowering oxidative stress in ghrelin cells stimulates ghrelin secretion

Ghrelin is a predominantly stomach-derived peptide hormone with many actions including regulation of food intake, body weight, and blood glucose. Plasma ghrelin levels are robustly regulated by feeding status, with its levels increasing upon caloric restriction and decreasing after food intake. At least some of this regulation might be due to direct responsiveness of ghrelin cells to changes in circulating nutrients, including glucose. Indeed, oral and parental glucose administration to humans and mice lower plasma ghrelin. Also, dissociated mouse gastric mucosal cell preparations, which contain ghrelin cells, decrease ghrelin secretion when cultured in high ambient glucose. Here, we used primary cultures of mouse gastric mucosal cells in combination with an array of pharmacological tools to examine the potential role of changed intracellular oxidative stress in glucose-restricted ghrelin secretion. The antioxidants resveratrol, SRT1720, and curcumin all markedly increased ghrelin secretion. Furthermore, three different selective activators of Nuclear factor erythroid-derived-2-like 2 (Nrf2), a master regulator of the antioxidative cellular response to oxidative stress, increased ghrelin secretion. These antioxidant compounds blocked the inhibitory effects of glucose on ghrelin secretion. Therefore, we conclude that lowering oxidative stress within ghrelin cells stimulates ghrelin secretion and blocks the direct effects of glucose on ghrelin cells to inhibit ghrelin secretion.

LEAP2 changes with body mass and food intake in humans and mice

Acyl-ghrelin administration increases food intake, body weight, and blood glucose. In contrast, mice lacking ghrelin or ghrelin receptors (GHSRs) exhibit life-threatening hypoglycemia during starvation-like conditions, but do not consistently exhibit overt metabolic phenotypes when given ad libitum food access. These results, and findings of ghrelin resistance in obese states, imply nutritional state dependence of ghrelin's metabolic actions. Here, we hypothesized that liver-enriched antimicrobial peptide-2 (LEAP2), a recently characterized endogenous GHSR antagonist, blunts ghrelin action during obese states and postprandially. To test this hypothesis, we determined changes in plasma LEAP2 and acyl-ghrelin due to fasting, eating, obesity, Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), oral glucose administration, and type 1 diabetes mellitus (T1DM) using humans and/or mice. Our results suggest that plasma LEAP2 is regulated by metabolic status: its levels increased with body mass and blood glucose and decreased with fasting, RYGB, and in postprandial states following VSG. These changes were mostly opposite of those of acyl-ghrelin. Furthermore, using electrophysiology, we showed that LEAP2 both hyperpolarizes and prevents acyl-ghrelin from activating arcuate NPY neurons. We predict that the plasma LEAP2/acyl-ghrelin molar ratio may be a key determinant modulating acyl-ghrelin activity in response to body mass, feeding status, and blood glucose.

Metabolic insights from a GHSR-A203E mutant mouse model

Objective

Binding of ghrelin to its receptor, growth hormone secretagogue receptor (GHSR), stimulates GH release, induces eating, and increases blood glucose. These processes may also be influenced by constitutive (ghrelin-independent) GHSR activity, as suggested by findings in short people with naturally occurring GHSR-A204E mutations and reduced food intake and blood glucose in rodents administered GHSR inverse agonists, both of which impair constitutive GHSR activity. In this study, we aimed to more fully determine the physiologic relevance of constitutive GHSR activity.

Methods

We generated mice with a GHSR mutation that replaces alanine at position 203 with glutamate (GHSR-A203E), which corresponds to the previously described human GHSR-A204E mutation, and used them to conduct ex vivo neuronal electrophysiology and in vivo metabolic assessments. We also measured signaling within COS-7 and HEK293T cells transfected with wild-type GHSR (GHSR-WT) or GHSR-A203E constructs.

Results

In COS-7 cells, GHSR-A203E resulted in lower baseline IP₃ accumulation than GHSR-WT; ghrelin-induced IP₃ accumulation was observed in both constructs. In HEK293T cells co-transfected with voltage-gated Ca_V2.2 calcium channel complex, GHSR-A203E had no effect on basal Ca_V2.2 current density while GHSR-WT did; both GHSR-A203E and GHSR-WT inhibited Ca_V2.2 current in the presence of ghrelin. In cultured hypothalamic neurons from GHSR-A203E and GHSR-deficient mice, native calcium currents were greater than those in neurons from wild-type mice; ghrelin inhibited calcium currents in cultured hypothalamic neurons from both GHSR-A203E and wild-type mice. In brain slices, resting membrane potentials of arcuate NPY neurons from GHSR-A203E mice were hyperpolarized compared to those from wild-type mice; the same percentage of arcuate NPY neurons from GHSR-A203E and wild-type mice depolarized upon ghrelin exposure. The GHSR-A203E mutation did not significantly affect body weight, body length, or femur length in the first ∼6 months of life, yet these parameters were lower in GHSR-A203E mice after 1 year of age. During a 7-d 60% caloric restriction regimen, GHSR-A203E mice lacked the usual marked rise in plasma GH and demonstrated an exaggerated drop in blood glucose. Administered ghrelin also exhibited reduced orexigenic and GH secretagogue efficacies in GHSR-A203E mice.

Conclusions

Our data suggest that the A203E mutation ablates constitutive GHSR activity and that constitutive GHSR activity contributes to the native depolarizing conductance of GHSR-expressing arcuate NPY neurons. Although the A203E mutation does not block ghrelin-evoked signaling as assessed using in vitro and ex vivo models, GHSR-A203E mice lack the usual acute food intake response to administered ghrelin in vivo. The GHSR-A203E mutation also blunts GH release, and in aged mice leads to reduced body length and femur length, which are consistent with the short stature of human carriers of the GHSR-A204E mutation.

•

We generated mice with a GHSR mutation replacing Ala at position 203 with Glu.

•

The A203E mutation ablates constitutive GHSR activity & hyperpolarizes NPY neurons.

•

GHSR-A203E mice lack the usual orexigenic response to administered ghrelin.

•

The GHSR-A203E mutation blunts GH release and causes reduced body length.

•

This finding is consistent with short stature in human carriers of the GHSR-A204E mutation.

Acyl-ghrelin Is Permissive for the Normal Counterregulatory Response to Insulin-Induced Hypoglycemia

Insulin-induced hypoglycemia leads to far-ranging negative consequences in patients with diabetes. Components of the counterregulatory response (CRR) system that help minimize and reverse hypoglycemia and coordination between those components are well studied but not yet fully characterized. Here, we tested the hypothesis that acyl-ghrelin, a hormone that defends against hypoglycemia in a preclinical starvation model, is permissive for the normal CRR to insulin-induced hypoglycemia. Ghrelin knockout (KO) mice and wild-type (WT) littermates underwent an insulin bolus-induced hypoglycemia test and a low-dose hyperinsulinemic-hypoglycemic clamp procedure. Clamps also were performed in ghrelin-KO mice and C57BL/6N mice administered the growth hormone secretagogue receptor agonist HM01 or vehicle. Results show that hypoglycemia, as induced by an insulin bolus, was more pronounced and prolonged in ghrelin-KO mice, supporting previous studies suggesting increased insulin sensitivity upon ghrelin deletion. Furthermore, during hyperinsulinemic-hypoglycemic clamps, ghrelin-KO mice required a 10-fold higher glucose infusion rate (GIR) and exhibited less robust corticosterone and growth hormone responses. Conversely, HM01 administration, which reduced the GIR required by ghrelin-KO mice during the clamps, increased plasma corticosterone and growth hormone. Thus, our data suggest that endogenously produced acyl-ghrelin not only influences insulin sensitivity but also is permissive for the normal CRR to insulin-induced hypoglycemia.

Ghrelin Protects Against Insulin-Induced Hypoglycemia in a Mouse Model of Type 1 Diabetes Mellitus

Insulin-induced hypoglycemia is a major limiting factor in maintaining optimal blood glucose in patients with type 1 diabetes and advanced type 2 diabetes. Luckily, a counterregulatory response (1) system exists to help minimize and reverse hypoglycemia, although more studies are needed to better characterize its components. Recently, we showed that the hormone ghrelin is permissive for the normal CRR to insulin-induced hypoglycemia when assessed in mice without diabetes. Here, we tested the hypothesis that ghrelin also is protective against insulin-induced hypoglycemia in the streptozotocin (2) mouse model of type 1 diabetes. STZ-treated ghrelin-knockout (KO) (3) mice as well as STZ-treated wild-type (WT) littermates were subjected to a low-dose hyperinsulinemic-hypoglycemic clamp procedure. The STZ-treated ghrelin-KO mice required a much higher glucose infusion rate than the STZ-treated WT mice. Also, the STZ-treated ghrelin-KO mice exhibited attenuated plasma epinephrine and norepinephrine responses to the insulin-induced hypoglycemia. Taken together, our data suggest that without ghrelin, STZ-treated mice modeling type 1 diabetes are unable to mount the usual CRR to insulin-induced hypoglycemia.

Combined Loss of Ghrelin Receptor and Cannabinoid CB1 Receptor in Mice Decreases Survival but does not Additively Reduce Body Weight or Eating

Ghrelin administration increases food intake, body weight (BW), adiposity, and blood glucose. In contrast, although mouse models lacking ghrelin or its receptor (Growth Hormone Secretagogue Receptor (GHSR)) exhibit life-threatening hypoglycemia in starvation-like states, they do not exhibit appreciable reductions in food intake, BW, adiposity, blood glucose, or survival when food availability is unrestricted. This suggests the existence of a parallel neuromodulatory system that can compensate for disruptions in the ghrelin system in certain settings. Here, we hypothesized that the cannabinoid CB1 receptor (CB1R) may encode this putative redundancy, and as such, that genetic deletion of both GHSR and CB1R would exaggerate the metabolic deficits associated with deletion of GHSR alone. To test this hypothesis, we assessed food intake, BW, blood glucose, survival, and plasma acyl-ghrelin in ad libitum-fed male wild-type mice and those that genetically lack GHSR (GHSR-nulls), CB1R (CB1R-nulls), or both GHSR and CB1R (double-nulls). BW, fat mass, and lean mass were similar in GHSR-nulls and wild-types, lower in CB1R-nulls, but not further reduced in double-nulls. Food intake, plasma acyl-ghrelin, and blood glucose were similar among genotypes. Deletion of either GHSR or CB1R alone did not have a statistically-significant effect on survival, but double-nulls demonstrated a statistical trend towards decreased survival (p = 0.07). We conclude that CB1R is not responsible for the normal BW, adiposity, food intake, and blood glucose observed in GHSR-null mice in the setting of unrestricted food availability. Nor is CB1R required for plasma acyl-ghrelin secretion in that setting. However, GHSR may be protective against exaggerated mortality associated with CB1R deletion.

β1-adrenergic receptors mediate plasma acyl-ghrelin elevation and depressive-like behavior induced by chronic psychosocial stress

The ghrelin system is a key component of the mood and metabolic responses to chronic psychosocial stress. For example, circulating acyl-ghrelin rises in several rodent and human stress models, administered acyl-ghrelin induces antidepressant-like behavioral responses in mice, and mice with deleted ghrelin receptors (GHSRs) exhibit exaggerated depressive-like behaviors, changed eating behaviors, and altered metabolism in response to chronic stress. However, the mechanisms mediating stress-induced rises in ghrelin are unknown and ghrelin's antidepressant-like efficacy in the setting of chronic stress is incompletely characterized. Here, we used a pharmacological approach in combination with a 10-day chronic social defeat stress (CSDS) model in male mice to investigate whether the sympathoadrenal system is involved in the ghrelin response to stress. We also examined the antidepressant-like efficacy of administered ghrelin and the synthetic GHSR agonist GHRP-2 during and/or after CSDS. We found that administration of the β1-adrenergic receptor (β1AR) blocker atenolol during CSDS blunts the elevation of plasma acyl-ghrelin and exaggerates depressive-like behavior. Neither acute injection of acyl-ghrelin directly following CSDS nor its chronic administration during or after CSDS nor chronic delivery of GHRP-2 during and after CSDS improved stress-induced depressive-like behavior. Thus, β1ARs drive the acyl-ghrelin response to CSDS, but supplementing the natural increases in acyl-ghrelin with exogenous acyl-ghrelin or GHSR agonist does not further enhance the antidepressant-like actions of the endogenous ghrelin system in the setting of CSDS.

Ghrelin Receptor Agonist Rescues Excess Neonatal Mortality in a Prader-Willi Syndrome Mouse Model

In the current study, we sought to determine the significance of the ghrelin system in Prader-Willi Syndrome (PWS). PWS is characterized by hypotonia and difficulty feeding in neonates and hyperphagia and obesity beginning later in childhood. Other features include low GH, neonatal hypoglycemia, hypogonadism, and accelerated mortality. Although the hyperphagia and obesity in PWS have been attributed to elevated levels of the orexigenic hormone ghrelin, this link has never been firmly established, nor have ghrelin's potentially protective actions to increase GH secretion, blood glucose, and survival been investigated in a PWS context. In the current study, we show that placing Snord116del mice modeling PWS on ghrelin-deficient or ghrelin receptor [GH secretagogue receptor (GHSR)]-deficient backgrounds does not impact their characteristically reduced body weight, lower plasma IGF-1, delayed sexual maturation, or increased mortality in the period prior to weaning. However, blood glucose was further reduced in male Snord116del pups on a ghrelin-deficient background, and percentage body weight gain and percentage fat mass were further reduced in male Snord116del pups on a GHSR-deficient background. Strikingly, 2 weeks of daily administration of the GHSR agonist HM01 to Snord116del neonates markedly improved survival, resulting in a nearly complete rescue of the excess mortality owing to loss of the paternal Snord116 gene. These data support further exploration of the therapeutic potential of GHSR agonist administration in limiting PWS mortality, especially during the period characterized by failure to thrive.

Ghrelin mediates exercise endurance and the feeding response post-exercise

Objective

Exercise training has several well-established health benefits, including many related to body weight, appetite control, and blood glucose homeostasis. However, the molecular mechanisms and, in particular, the hormonal systems that mediate and integrate these beneficial effects are poorly understood. In the current study, we aimed to investigate the role of the hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR; ghrelin receptor), in mediating the effects of exercise on food intake and blood glucose following exercise as well as in regulating exercise endurance capacity.

Methods

We used two mouse models of treadmill running to characterize the changes in plasma ghrelin with exercise. We also assessed the role of the ghrelin system to influence food intake and blood glucose after exercise, exercise endurance, and parameters potentially linked to responses to exercise. Mice lacking GHSRs (GHSR-null mice) and wild-type littermates were studied.

Results

An acute bout of exercise transiently elevated plasma acyl-ghrelin. Without the action of this increased ghrelin on GHSRs (as in GHSR-null mice), high intensity interval exercise markedly reduced food intake compared to control mice. The effect of exercise to acutely raise blood glucose remained unmodified in GHSR-null mice. Exercise-induced increases in plasma ghrelin positively correlated with endurance capacity, and time to exhaustion was reduced in GHSR-null mice as compared to wild-type littermates. In an effort to mechanistically explain their reduced exercise endurance, exercised GHSR-null mice exhibited an abrogated sympathoadrenal response, lower overall insulin-like growth factor-1 levels, and altered glycogen utilization.

Conclusions

Exercise transiently increases plasma ghrelin. GHSR-null mice exhibit decreased food intake following high intensity interval exercise and decreased endurance when submitted to an exercise endurance protocol. These data suggest that an intact ghrelin system limits the capacity of exercise to restrict food intake following exercise, although it enhances exercise endurance.

•

High intensity exercise transiently increases plasma ghrelin.

•

Without ghrelin action on its receptors (growth hormone secretagogue receptors), exercise markedly reduces food intake.

•

An intact ghrelin system enhances exercise endurance.

Hypoglycemic Effect of Combined Ghrelin and Glucagon Receptor Blockade

Glucagon receptor (GcgR) blockade has been proposed as an alternative to insulin monotherapy for treating type 1 diabetes since deletion or inhibition of GcgRs corrects hyperglycemia in models of diabetes. The factors regulating glycemia in a setting devoid of insulin and glucagon function remain unclear but may include the hormone ghrelin. Not only is ghrelin release controlled by glucose but also ghrelin has many actions that can raise or reduce falls in blood glucose level. Here, we tested the hypothesis that ghrelin rises to prevent hypoglycemia in the absence of glucagon function. Both GcgR knockout (Gcgr^-/-) mice and db/db mice that were administered GcgR monoclonal antibody displayed lower blood glucose levels accompanied by elevated plasma ghrelin levels. Although treatment with the pancreatic β-cell toxin streptozotocin induced hyperglycemia and raised plasma ghrelin levels in wild-type mice, hyperglycemia was averted in similarly treated Gcgr^-/- mice and the plasma ghrelin level was further increased. Notably, administration of a ghrelin receptor antagonist further reduced blood glucose levels into the markedly hypoglycemic range in overnight-fasted, streptozotocin-treated Gcgr^-/- mice. A lowered blood glucose level also was observed in overnight-fasted, streptozotocin-treated ghrelin receptor-null mice that were administered GcgR monoclonal antibody. These data suggest that when glucagon activity is blocked in the setting of type 1 diabetes, the plasma ghrelin level rises, preventing hypoglycemia.

β1-Adrenergic receptor deficiency in ghrelin-expressing cells causes hypoglycemia in susceptible individuals

Ghrelin is an orexigenic gastric peptide hormone secreted when caloric intake is limited. Ghrelin also regulates blood glucose, as emphasized by the hypoglycemia that is induced by caloric restriction in mouse models of deficient ghrelin signaling. Here, we hypothesized that activation of β1-adrenergic receptors (β1ARs) localized to ghrelin cells is required for caloric restriction-associated ghrelin release and the ensuing protective glucoregulatory response. In mice lacking the β1AR specifically in ghrelin-expressing cells, ghrelin secretion was markedly blunted, resulting in profound hypoglycemia and prevalent mortality upon severe caloric restriction. Replacement of ghrelin blocked the effects of caloric restriction in β1AR-deficient mice. We also determined that treating calorically restricted juvenile WT mice with beta blockers led to reduced plasma ghrelin and hypoglycemia, the latter of which is similar to the life-threatening, fasting-induced hypoglycemia observed in infants treated with beta blockers. These findings highlight the critical functions of ghrelin in preventing hypoglycemia and promoting survival during severe caloric restriction and the requirement for ghrelin cell-expressed β1ARs in these processes. Moreover, these results indicate a potential role for ghrelin in mediating beta blocker-associated hypoglycemia in susceptible individuals, such as young children.

Research Resource: A Chromogranin A Reporter for Serotonin and Histamine Secreting Enteroendocrine Cells

Chromogranin A (ChgA) is an acidic protein found in large dense-core secretory vesicles and generally considered to be expressed in all enteroendocrine cells of the gastrointestinal (GI) tract. Here, we characterize a novel reporter mouse for ChgA, ChgA-humanized Renilla reniformis (hr)GFP. The hrGFP reporter was found in the monoamine-storing chromaffin cells of the adrenal medulla, where ChgA was originally discovered. hrGFP also was expressed in enteroendocrine cells throughout the GI tract, faithfully after the expression of ChgA, as characterized by immunohistochemistry and quantitative PCR analysis of fluorescence-activated cell sorting-purified cells, although the expression in the small intestine was weak compared with that of the stomach and colon. In the stomach, hrGFP was highly expressed in almost all histamine-storing enterochromaffin (EC)-like cells, at a lower level in the majority of serotonin-storing EC cells and ghrelin cells, in a small fraction of somatostatin cells, but was absent from gastrin cells. In the small intestine, the hrGFP reporter was selectively, but weakly expressed in EC cells, although not in any peptide-storing enteroendocrine cells. In the colon, hrGFP was exclusively expressed in EC cells but absent from the peptide-storing enteroendocrine cells. In contrast, in the pancreas, hrGFP was expressed in β-cells, α-cells, and a fraction of pancreatic polypeptide cells. It is concluded that ChgA-hrGFP in the GI tract functions as an effective reporter, particularly for the large populations of still poorly characterized monoamine-storing enteroendocrine cells. Furthermore, our findings substantiate the potential function of ChgA as a monoamine-binding protein that facilitates the regulated endocrine secretion of large amounts of monoamines from enteroendocrine cells.

Role of calcium and EPAC in norepinephrine-induced ghrelin secretion

Ghrelin is an orexigenic hormone secreted principally from a distinct population of gastric endocrine cells. Molecular mechanisms regulating ghrelin secretion are mostly unknown. Recently, norepinephrine (NE) was shown to enhance ghrelin release by binding to β1-adrenergic receptors on ghrelin cells. Here, we use an immortalized stomach-derived ghrelin cell line to further characterize the intracellular signaling pathways involved in NE-induced ghrelin secretion, with a focus on the roles of Ca(2+) and cAMP. Several voltage-gated Ca(2+) channel (VGCC) family members were found by quantitative PCR to be expressed by ghrelin cells. Nifedipine, a selective L-type VGCC blocker, suppressed both basal and NE-stimulated ghrelin secretion. NE induced elevation of cytosolic Ca(2+) levels both in the presence and absence of extracellular Ca(2+). Ca(2+)-sensing synaptotagmins Syt7 and Syt9 were also highly expressed in ghrelin cell lines, suggesting that they too help mediate ghrelin secretion. Raising cAMP with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine also stimulated ghrelin secretion, although such a cAMP-mediated effect likely does not involve protein kinase A, given the absence of a modulatory response to a highly selective protein kinase A inhibitor. However, pharmacological inhibition of another target of cAMP, exchange protein-activated by cAMP (EPAC), did attenuate both basal and NE-induced ghrelin secretion, whereas an EPAC agonist enhanced basal ghrelin secretion. We conclude that constitutive ghrelin secretion is primarily regulated by Ca(2+) influx through L-type VGCCs and that NE stimulates ghrelin secretion predominantly through release of intracellular Ca(2+). Furthermore, cAMP and its downstream activation of EPAC are required for the normal ghrelin secretory response to NE.

Arcuate AgRP neurons mediate orexigenic and glucoregulatory actions of ghrelin

The hormone ghrelin stimulates eating and helps maintain blood glucose upon caloric restriction. While previous studies have demonstrated that hypothalamic arcuate AgRP neurons are targets of ghrelin, the overall relevance of ghrelin signaling within intact AgRP neurons is unclear. Here, we tested the functional significance of ghrelin action on AgRP neurons using a new, tamoxifen-inducible AgRP-CreER^T2 transgenic mouse model that allows spatiotemporally-controlled re-expression of physiological levels of ghrelin receptors (GHSRs) specifically in AgRP neurons of adult GHSR-null mice that otherwise lack GHSR expression. AgRP neuron-selective GHSR re-expression partially restored the orexigenic response to administered ghrelin and fully restored the lowered blood glucose levels observed upon caloric restriction. The normalizing glucoregulatory effect of AgRP neuron-selective GHSR expression was linked to glucagon rises and hepatic gluconeogenesis induction. Thus, our data indicate that GHSR-containing AgRP neurons are not solely responsible for ghrelin's orexigenic effects but are sufficient to mediate ghrelin's effects on glycemia.

Seven transmembrane G protein-coupled receptor repertoire of gastric ghrelin cells

The molecular mechanisms regulating secretion of the orexigenic-glucoregulatory hormone ghrelin remain unclear. Based on qPCR analysis of FACS-purified gastric ghrelin cells, highly expressed and enriched 7TM receptors were comprehensively identified and functionally characterized using in vitro, ex vivo and in vivo methods. Five Gαs-coupled receptors efficiently stimulated ghrelin secretion: as expected the β1-adrenergic, the GIP and the secretin receptors but surprisingly also the composite receptor for the sensory neuropeptide CGRP and the melanocortin 4 receptor. A number of Gαi/o-coupled receptors inhibited ghrelin secretion including somatostatin receptors SSTR1, SSTR2 and SSTR3 and unexpectedly the highly enriched lactate receptor, GPR81. Three other metabolite receptors known to be both Gαi/o- and Gαq/11-coupled all inhibited ghrelin secretion through a pertussis toxin-sensitive Gαi/o pathway: FFAR2 (short chain fatty acid receptor; GPR43), FFAR4 (long chain fatty acid receptor; GPR120) and CasR (calcium sensing receptor). In addition to the common Gα subunits three non-common Gαi/o subunits were highly enriched in ghrelin cells: GαoA, GαoB and Gαz. Inhibition of Gαi/o signaling via ghrelin cell-selective pertussis toxin expression markedly enhanced circulating ghrelin. These 7TM receptors and associated Gα subunits constitute a major part of the molecular machinery directly mediating neuronal and endocrine stimulation versus metabolite and somatostatin inhibition of ghrelin secretion including a series of novel receptor targets not previously identified on the ghrelin cell.

Leptin signaling in Kiss1 neurons arises after pubertal development

The adipocyte-derived hormone leptin is required for normal pubertal maturation in mice and humans and, therefore, leptin has been recognized as a crucial metabolic cue linking energy stores and the onset of puberty. Several lines of evidence have suggested that leptin acts via kisspeptin expressing neurons of the arcuate nucleus to exert its effects. Using conditional knockout mice, we have previously demonstrated that deletion of leptin receptors (LepR) from kisspeptin cells cause no puberty or fertility deficits. However, developmental adaptations and system redundancies may have obscured the physiologic relevance of direct leptin signaling in kisspeptin neurons. To overcome these putative effects, we re-expressed endogenous LepR selectively in kisspeptin cells of mice otherwise null for LepR, using the Cre-loxP system. Kiss1-Cre LepR null mice showed no pubertal development and no improvement of the metabolic phenotype, remaining obese, diabetic and infertile. These mice displayed decreased numbers of neurons expressing Kiss1 gene, similar to prepubertal control mice, and an unexpected lack of re-expression of functional LepR. To further assess the temporal coexpression of Kiss1 and Lepr genes, we generated mice with the human renilla green fluorescent protein (hrGFP) driven by Kiss1 regulatory elements and crossed them with mice that express Cre recombinase from the Lepr locus and the R26-tdTomato reporter gene. No coexpression of Kiss1 and LepR was observed in prepubertal mice. Our findings unequivocally demonstrate that kisspeptin neurons are not the direct target of leptin in the onset of puberty. Leptin signaling in kisspeptin neurons arises only after completion of sexual maturation.

Glucose-mediated control of ghrelin release from primary cultures of gastric mucosal cells

The peptide hormone ghrelin is released from a distinct group of gastrointestinal cells in response to caloric restriction, whereas its levels fall after eating. The mechanisms by which ghrelin secretion is regulated remain largely unknown. Here, we have used primary cultures of mouse gastric mucosal cells to investigate ghrelin secretion, with an emphasis on the role of glucose. Ghrelin secretion from these cells upon exposure to different d-glucose concentrations, the glucose antimetabolite 2-deoxy-d-glucose, and other potential secretagogues was assessed. The expression profile of proteins involved in glucose transport, metabolism, and utilization within highly enriched pools of mouse ghrelin cells and within cultured ghrelinoma cells was also determined. Ghrelin release negatively correlated with d-glucose concentration. Insulin blocked ghrelin release, but only in a low d-glucose environment. 2-Deoxy-d-glucose prevented the inhibitory effect of high d-glucose exposure on ghrelin release. mRNAs encoding several facilitative glucose transporters, hexokinases, the ATP-sensitive potassium channel subunit Kir6.2, and sulfonylurea type 1 receptor were expressed highly within ghrelin cells, although neither tolbutamide nor diazoxide exerted direct effects on ghrelin secretion. These findings suggest that direct exposure of ghrelin cells to low ambient d-glucose stimulates ghrelin release, whereas high d-glucose and glucose metabolism within ghrelin cells block ghrelin release. Also, low d-glucose sensitizes ghrelin cells to insulin. Various glucose transporters, channels, and enzymes that mediate glucose responsiveness in other cell types may contribute to the ghrelin cell machinery involved in regulating ghrelin secretion under these different glucose environments, although their exact roles in ghrelin release remain uncertain.

Proton- and ammonium-sensing by histaminergic neurons controlling wakefulness

The histaminergic neurons in the tuberomamillary nucleus (TMN) of the posterior hypothalamus are involved in the control of arousal. These neurons are sensitive to hypercapnia as has been shown in experiments examining c-Fos expression, a marker for increased neuronal activity. We investigated the mechanisms through which TMN neurons respond to changes in extracellular levels of acid/CO₂. Recordings in rat brain slices revealed that acidification within the physiological range (pH from 7.4 to 7.0), as well as ammonium chloride (5 mM), excite histaminergic neurons. This excitation is significantly reduced by antagonists of type I metabotropic glutamate receptors and abolished by benzamil, an antagonist of acid-sensing ion channels (ASICs) and Na⁺/Ca²⁺ exchanger, or by ouabain which blocks Na⁺/K⁺ ATPase. We detected variable combinations of 4 known types of ASICs in single TMN neurons, and observed activation of ASICs in single dissociated TMN neurons only at pH lower than 7.0. Thus, glutamate, which is known to be released by glial cells and orexinergic neurons, amplifies the acid/CO₂-induced activation of TMN neurons. This amplification demands the coordinated function of metabotropic glutamate receptors, Na⁺/Ca²⁺ exchanger and Na⁺/K⁺ ATPase. We also developed a novel HDC-Cre transgenic reporter mouse line in which histaminergic TMN neurons can be visualized. In contrast to the rat, the mouse histaminergic neurons lacked the pH 7.0-induced excitation and displayed only a minimal response to the mGluR I agonist DHPG (0.5 μM). On the other hand, ammonium-induced excitation was similar in mouse and rat. These results are relevant for the understanding of the neuronal mechanisms controlling acid/CO₂-induced arousal in hepatic encephalopathy and obstructive sleep apnoea. Moreover, the new HDC-Cre mouse model will be a useful tool for studying the physiological and pathophysiological roles of the histaminergic system.

Functional implications of limited leptin receptor and ghrelin receptor coexpression in the brain

The hormones leptin and ghrelin act in apposition to one another in the regulation of body weight homeostasis. Interestingly, both leptin receptor expression and ghrelin receptor expression have been observed within many of the same nuclei of the central nervous system (CNS), suggesting that these hormones may act on a common population of neurons to produce changes in food intake and energy expenditure. In the present study we explored the extent of this putative direct leptin and ghrelin interaction in the CNS and addressed the question of whether a loss of ghrelin signaling would affect sensitivity to leptin. Using histological mapping of leptin receptor and ghrelin receptor expression, we found that cells containing both leptin receptors and ghrelin receptors are mainly located in the medial part of the hypothalamic arcuate nucleus. In contrast, coexpression was much less extensive elsewhere in the brain. To assess the functional consequences of this observed receptor distribution, we explored the effect of ghrelin receptor deletion on leptin sensitivity. In particular, the responses of ad libitum-fed, diet-induced obese and fasted mice to the anorectic actions of leptin were examined. Surprisingly, we found that deletion of the ghrelin receptor did not affect the sensitivity to exogenously administrated leptin. Thus, we conclude that ghrelin and leptin act largely on distinct neuronal populations and that ghrelin receptor deficiency does not affect sensitivity to the anorexigenic and body weight-lowering actions of leptin.

Ghrelin directly stimulates glucagon secretion from pancreatic alpha-cells

Previous work has demonstrated that the peptide hormone ghrelin raises blood glucose. Such has been attributed to ghrelin's ability to enhance GH secretion, restrict insulin release, and/or reduce insulin sensitivity. Ghrelin's reported effects on glucagon have been inconsistent. Here, both animal- and cell-based systems were used to determine the role of glucagon in mediating ghrelin's effects on blood glucose. The tissue and cell distribution of ghrelin receptors (GHSR) was evaluated by quantitative PCR and histochemistry. Plasma glucagon levels were determined following acute acyl-ghrelin injections and in pharmacological and/or transgenic mouse models of ghrelin overexpression and GHSR deletion. Isolated mouse islets and the α-cell lines αTC1 and InR1G9 were used to evaluate ghrelin's effects on glucagon secretion and the role of calcium and ERK in this activity. GHSR mRNA was abundantly expressed in mouse islets and colocalized with glucagon in α-cells. Elevation of acyl-ghrelin acutely (after sc administration, such that physiologically relevant plasma ghrelin levels were achieved) and chronically (by slow-releasing osmotic pumps and as observed in transgenic mice harboring ghrelinomas) led to higher plasma glucagon and increased blood glucose. Conversely, genetic GHSR deletion was associated with lower plasma glucagon and reduced fasting blood glucose. Acyl-ghrelin increased glucagon secretion in a dose-dependent manner from mouse islets and α-cell lines, in a manner requiring elevation of intracellular calcium and phosphorylation of ERK. Our study shows that ghrelin's regulation of blood glucose involves direct stimulation of glucagon secretion from α-cells and introduces the ghrelin-glucagon axis as an important mechanism controlling glycemia under fasting conditions.

Ghrelin mediates stress-induced food-reward behavior in mice

The popular media and personal anecdotes are rich with examples of stress-induced eating of calorically dense "comfort foods." Such behavioral reactions likely contribute to the increased prevalence of obesity in humans experiencing chronic stress or atypical depression. However, the molecular substrates and neurocircuits controlling the complex behaviors responsible for stress-based eating remain mostly unknown, and few animal models have been described for probing the mechanisms orchestrating this response. Here, we describe a system in which food-reward behavior, assessed using a conditioned place preference (CPP) task, is monitored in mice after exposure to chronic social defeat stress (CSDS), a model of prolonged psychosocial stress, featuring aspects of major depression and posttraumatic stress disorder. Under this regime, CSDS increased both CPP for and intake of high-fat diet, and stress-induced food-reward behavior was dependent on signaling by the peptide hormone ghrelin. Also, signaling specifically in catecholaminergic neurons mediated not only ghrelin's orexigenic, antidepressant-like, and food-reward behavioral effects, but also was sufficient to mediate stress-induced food-reward behavior. Thus, this mouse model has allowed us to ascribe a role for ghrelin-engaged catecholaminergic neurons in stress-induced eating.

Characterization of Kiss1 neurons using transgenic mouse models

Humans and mice with loss-of-function mutations of the genes encoding kisspeptins (Kiss1) or kisspeptin receptor (Kiss1r) are infertile due to hypogonadotropic hypogonadism. Within the hypothalamus, Kiss1 mRNA is expressed in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (Arc). In order to better study the different populations of kisspeptin cells we generated Kiss1-Cre transgenic mice. We obtained one line with Cre activity specifically within Kiss1 neurons (line J2-4), as assessed by generating mice with Cre-dependent expression of green fluorescent protein or β-galactosidase. Also, we demonstrated Kiss1 expression in the cerebral cortex and confirmed previous data showing Kiss1 mRNA in the medial nucleus of amygdala and anterodorsal preoptic nucleus. Kiss1 neurons were more concentrated towards the caudal levels of the Arc and higher leptin-responsivity was observed in the most caudal population of Arc Kiss1 neurons. No evidence for direct action of leptin in AVPV Kiss1 neurons was observed. Melanocortin fibers innervated subsets of Kiss1 neurons of the preoptic area and Arc, and both populations expressed melanocortin receptors type 4 (MC4R). Specifically in the preoptic area, 18-28% of Kiss1 neurons expressed MC4R. In the Arc, 90% of Kiss1 neurons were glutamatergic, 50% of which also were GABAergic. In the AVPV, 20% of Kiss1 neurons were glutamatergic whereas 75% were GABAergic. The differences observed between the Kiss1 neurons in the preoptic area and the Arc likely represent neuronal evidence for their differential roles in metabolism and reproduction.

Ghrelin increases the rewarding value of high-fat diet in an orexin-dependent manner

BACKGROUND

Ghrelin is a potent orexigenic hormone that likely impacts eating via several mechanisms. Here, we hypothesized that ghrelin can regulate extra homeostatic, hedonic aspects of eating behavior.

METHODS

In the current study, we assessed the effects of different pharmacological, physiological, and genetic models of increased ghrelin and/or ghrelin-signaling blockade on two classic behavioral tests of reward behavior: conditioned place preference (CPP) and operant conditioning.

RESULTS

Using both CPP and operant conditioning, we found that ghrelin enhanced the rewarding value of high-fat diet (HFD) when administered to ad lib-fed mice. Conversely, wild-type mice treated with ghrelin receptor antagonist and ghrelin receptor-null mice both failed to show CPP to HFD normally observed under calorie restriction. Interestingly, neither pharmacologic nor genetic blockade of ghrelin signaling inhibited the body weight homeostasis-related, compensatory hyperphagia associated with chronic calorie restriction. Also, ghrelin's effects on HFD reward were blocked in orexin-deficient mice and wild-type mice treated with an orexin 1 receptor antagonist.

CONCLUSIONS

Our results demonstrate an obligatory role for ghrelin in certain rewarding aspects of eating that is separate from eating associated with body weight homeostasis and that requires the presence of intact orexin signaling.

Colocalization of ghrelin O-acyltransferase and ghrelin in gastric mucosal cells

Ghrelin is a peptide hormone with many known functions, including orexigenic, blood glucose-regulatory, and antidepressant actions, among others. Mature ghrelin is unique in that it is the only known naturally occurring peptide to be posttranslationally modified by O-acylation with octanoate. This acylation is required for many of ghrelin's actions, including its effects on promoting increases in food intake and body weight. GOAT (ghrelin O-acyltransferase), one of 16 members of the MBOAT family of membrane-bound O-acyltransferases, has recently been identified as the enzyme responsible for catalyzing the addition of the octanoyl group to ghrelin. Although the initial reports of GOAT have localized its encoding mRNA to tissues known to contain ghrelin, it is as yet unclear whether the octanoylation occurs within ghrelin-producing cells or in neighboring cells. Here, we have performed dual-label histochemical analysis on mouse stomach sections and quantitative PCR on mRNAs from highly enriched pools of mouse gastric ghrelin cells to demonstrate a high degree of GOAT mRNA expression within ghrelin-producing cells of the gastric oxyntic mucosa. We also demonstrate that GOAT is the only member of the MBOAT family whose expression is highly enriched within gastric ghrelin cells and whose whole body distribution mirrors that of ghrelin.

Characterization of a novel ghrelin cell reporter mouse

Ghrelin is a hormone that influences many physiological processes and behaviors, such as food intake, insulin and growth hormone release, and a coordinated response to chronic stress. However, little is known about the molecular pathways governing ghrelin release and ghrelin cell function. To better study ghrelin cell physiology, we have generated several transgenic mouse lines expressing humanized Renilla reniformis green fluorescent protein (hrGFP) under the control of the mouse ghrelin promoter. hrGFP expression was especially abundant in the gastric oxyntic mucosa, in a pattern mirroring that of ghrelin immunoreactivity and ghrelin mRNA. hrGFP expression also was observed in the duodenum, but not in the brain, pancreatic islet, or testis. In addition, we used fluorescent activated cell sorting (FACS) to collect and partially characterize highly enriched populations of gastric ghrelin cells. We suggest that these novel ghrelin-hrGFP transgenic mice will serve as useful tools to better understand ghrelin cell physiology.

C-reactive protein downregulates endothelial NO synthase and attenuates reendothelialization in vivo in mice

C-reactive protein (CRP) is an acute-phase reactant that is positively associated with cardiovascular disease risk and endothelial dysfunction. In cell culture, CRP decreases the expression of endothelial NO synthase (eNOS), which regulates diverse endothelial cell (EC) functions including migration. To determine whether CRP alters EC gene expression and phenotype in vivo, we studied CF1 transgenic mice expressing rabbit CRP (CF1-CRP) regulated by the phosphoenolpyruvate carboxykinase promoter such that levels could be altered by changing carbohydrate intake. Compared with CF1 controls with CRP of <1 microg/mL, carotid artery reendothelialization after perivascular electric injury was blunted in CF1-CRP mice, with CRP levels as low as 9 microg/mL. eNOS mRNA and enzyme abundance in carotid arteries was also blunted by CRP at 9 microg/mL in vivo, and ex vivo studies of isolated arteries showed that this occurs via direct action on the endothelium. The impaired reendothelialization with CRP was mimicked by NOS antagonism in CF1 mice; conversely, in cultured ECs CRP attenuation of migration was prevented by exogenous NO. Studies of EC transfected with human eNOS 5' flanking sequence fused to luciferase indicated that CRP decreases eNOS gene transcription. Both mutagenesis and electrophoretic mobility shift assays further revealed that CRP-responsive elements reside within the first 79 bp of the eNOS promoter. Thus, CRP downregulates eNOS and attenuates reendothelialization in vivo in mice, and this action of CRP on eNOS is mediated at the level of gene transcription.

C-reactive protein causes downregulation of vascular angiotensin subtype 2 receptors and systolic hypertension in mice

BACKGROUND

Chronic elevations in circulating C-reactive protein (CRP) are associated with a greater risk of hypertension. Whether elevations in CRP cause hypertension is unknown.

METHODS AND RESULTS

Chronic, conscious blood pressure (BP) measurements were performed by radiotelemetry in wild-type CF1 control and CF1 transgenic mice expressing rabbit CRP (CF1-CRP) under the regulation of the phosphoenolpyruvate carboxykinase promoter. Compared with controls, CF1-CRP mice had hypertension that was predominantly systolic, and the severity of hypertension varied in parallel with changes in CRP levels modulated by dietary manipulation. Mice that were hemizygous for the transgene with CRP levels of 9 microg/mL were also hypertensive, indicating that modest elevations in CRP are sufficient to alter BP. CRP transgenic mice had exaggerated BP elevation in response to angiotensin II and a reduction in vascular angiotensin receptor subtype 2 (AT2) expression. In contrast, the decline in BP with angiotensin receptor subtype 1 (AT1) antagonism and vascular AT1 abundance were unaltered, which indicates a selective effect of CRP on AT2. Ex vivo experiments further showed that the CRP-induced decrease in AT2 is a direct effect on the vascular wall, not requiring systemic responses, and that it is reversed by an NO donor, which indicates a role for NO deficiency in the process. In parallel, the chronic inhibition of NO synthase in wild-type mice attenuated vascular AT2 expression without affecting AT1.

CONCLUSIONS

These findings provide direct evidence for CRP-induced hypertension, and they further identify a novel underlying mechanism involving downregulation of AT2 related to NO deficiency.

FcγRIIB Mediates C-Reactive Protein Inhibition of Endothelial NO Synthase

C-reactive protein (CRP) is an acute-phase reactant that is positively correlated with cardiovascular disease risk and endothelial dysfunction. Whether CRP has direct actions on endothelium and the mechanisms underlying such actions are unknown. Here we show in cultured endothelium that CRP prevents endothelial NO synthase (eNOS) activation by diverse agonists, resulting in the promotion of monocyte adhesion. CRP antagonism of eNOS occurs nongenomically and is attributable to blunted eNOS phosphorylation at Ser1179. Okadaic acid or knockdown of PP2A by short-interference RNA reverses CRP antagonism of eNOS, indicating a key role for the phosphatase. Aggregated IgG, the known ligand for Fcγ receptors, causes parallel okadaic acid–sensitive loss of eNOS function, FcγRIIB expression is demonstrable in endothelium, and heterologous expression studies reveal that CRP antagonism of eNOS requires FcγRIIB. In FcγRIIB +/+ mice, CRP blunts acetylcholine-induced increases in carotid artery vascular conductance; in contrast, CRP enhances acetylcholine responses in FcγRIIB −/− mice. Thus FcγRIIB mediates CRP inhibition of eNOS via PP2A, providing a mechanistic link between CRP and endothelial dysfunction.

Inhaled NO improves early pulmonary function and modifies lung growth and elastin deposition in a baboon model of neonatal chronic lung disease

Nitric oxide (NO) serves multiple functions in the developing lung, and pulmonary NO production is decreased in a baboon model of chronic lung disease (CLD) after premature birth at 125 days (d) gestation (term = 185d). To determine whether postnatal NO administration alters the genesis of CLD, the effects of inhaled NO (iNO, 5 ppm) were assessed in the baboon model over 14d. iNO caused a decrease in pulmonary artery pressure in the first 2d and a greater rate of spontaneous closure of the ductus arteriosus, and lung compliance was greater and expiratory resistance was improved during the first week. With iNO, postmortem pressure-volume curves were shifted upward, lung DNA content and cell proliferation were increased, and lung growth was preserved to equal that which occurs during the same period in utero. In addition, the excessive elastin deposition characteristic of CLD was normalized by iNO, and there was evidence of stimulation of secondary crest development. Thus, in the baboon model of CLD, iNO improves early pulmonary function and alters lung growth and extracellular matrix deposition. As such, NO biosynthetic pathway dysfunction may contribute to the pathogenesis of CLD.

Molecular basis of estrogen-induced cyclooxygenase type 1 upregulation in endothelial cells

Estrogen upregulates cyclooxygenase-1 (COX-1) expression in endothelial cells. To determine the basis of this process, studies were performed in ovine endothelial cells transfected with the human COX-1 promoter fused to luciferase. Estradiol (E2) caused activation of the COX-1 promoter with maximal stimulation at 10(-8) mol/L E2, and the response was mediated by either ERalpha or ERbeta. Mutagenesis revealed a primary role for a putative Sp1 binding motif at -89 (relative to the ATG codon) and lesser involvement of a consensus Sp1 site at -111. Electrophoretic mobility shift assays yielded a single complex with the site at -89, and supershift analyses implicated AP-2alpha and ERalpha, and not Sp1, in protein-DNA complex formation. In endothelial cells with minimal endogenous ER, the transfection of ERalpha mutants lacking the DNA binding domain or primary nuclear localization signals caused 4-fold greater stimulation of promoter activity with E2 than wild-type ERalpha. In contrast, mutant ERalpha lacking the A-B domains was inactive. Thus, estrogen-mediated upregulation of COX-1 in endothelium is uniquely independent of direct ERalpha-DNA binding and instead entails protein-DNA interaction involving AP-2alpha and ERalpha at a proximal regulatory element. In addition, the process may be initiated by cytoplasmic ERalpha, and critical receptor elements reside within the amino terminus.

High-density lipoprotein binding to scavenger receptor-BI activates endothelial nitric oxide synthase

Atherosclerosis is the primary cause of cardiovascular disease, and the risk for atherosclerosis is inversely proportional to circulating levels of high-density lipoprotein (HDL) cholesterol. However, the mechanisms by which HDL is atheroprotective are complex and not well understood. Here we show that HDL stimulates endothelial nitric oxide synthase (eNOS) in cultured endothelial cells. In contrast, eNOS is not activated by purified forms of the major HDL apolipoproteins ApoA-I and ApoA-II or by low-density lipoprotein. Heterologous expression experiments in Chinese hamster ovary cells reveal that scavenger receptor-BI (SR-BI) mediates the effects of HDL on the enzyme. HDL activation of eNOS is demonstrable in isolated endothelial-cell caveolae where SR-BI and eNOS are colocalized, and the response in isolated plasma membranes is blocked by antibodies to ApoA-I and SR-BI, but not by antibody to ApoA-II. HDL also enhances endothelium- and nitric-oxide-dependent relaxation in aortae from wild-type mice, but not in aortae from homozygous null SR-BI knockout mice. Thus, HDL activates eNOS via SR-BI through a process that requires ApoA-I binding. The resulting increase in nitric-oxide production might be critical to the atheroprotective properties of HDL and ApoA-I.

Infrequency of BRCA2 alterations in head and neck squamous cell carcinoma

Alterations of BRCA2 result in increased susceptibility to breast cancer in both men and women (relative lifetime risks of 0.06 and 0.8 respectively). BRCA2 maps to 13q12-q13 and encodes a transcript of 10,157 bp. Other cancers that have been described in BRCA2 mutation carriers include those of the larynx. Human chromosome 13q has been shown previously by LOH studies to harbor several tumor suppressor genes for head and neck squamous cell carcinoma (HNSCCs). We therefore examined the role of BRCA2 in the development of these cancers. Only 6/22 (27%) of the laryngeal cancers we examined demonstrated LOH of the BRCA2-containing region. These and 10 other HNSCCs of different origins that were demonstrated by LOH studies to have lost the region of chromosome 13 containing BRCA2 were examined for alterations in this gene. SSCP analysis failed to reveal any alterations leading us to conclude that BRCA2 alterations are not frequently involved in the pathogenesis of HNSCCs and that the observed LOH of chromosome 13 loci is due to other, as yet, unidentified tumor suppressor gene(s). Interestingly tumors with LOH in this region (proximal to D13S118) were far more likely to be derived from women than men. This is unusual since HNSCCs are usually fourfold more common in men than in women.

Characterization of EZH1, a human homolog of Drosophila Enhancer of zeste near BRCA1

Recent transcription mapping efforts within chromosome 17q21 have led to the identification of a human homolog of the Drosophila gene Enhancer of zeste, E(z). A member of the Polycomb group (Pc-G) of proteins, Drosophila E(z) acts as a negative regulator of the segment identity genes of the Antennapedia and Bithorax complexes. Here we report the full-length protein coding sequence of human EZH1 (Enhancer of zeste homolog 1) and compare the respective protein sequences in both species. EZH1 encodes a protein of 747 amino acids that displays 55% amino acid identity overall (70% similarity) with Drosophila E(z). The strongest homology was noted (79% identity, 89% similarity) within the carboxy-terminal 245 amino acids, including the SET domain, a region of E(z) also conserved in other Drosophila proteins with roles in development and/or chromatin structure. A large Cysrich region with a novel spatial pattern of cysteine residues was also conserved in both EZH1 and E(z). The strong sequence conservation suggest potential roles for EZH1 in human development as a transcriptional regulator and as a component of protein complexes that stably maintain heterochromatin. EZH1 is expressed as two major transcripts in all adult and fetal human tissues surveyed; comparison of cloned cDNAs suggests that alternative splicing may account for at least part of the transcript size difference. Analysis of one cDNA revealed an unusual splicing event involving EZH1 and a tandemly linked gene GPR2 and suggests a potential mechanism for modifying the EZH1 protein in the conserved C-terminal domain. The sequence and isolated cDNAs will provide useful reagents for determining the function of EZH1 and the importance of the evolutionarily conserved domains.

A high-resolution annotated physical map of the human chromosome 13q12-13 region containing the breast cancer susceptibility locus BRCA2

Various types of physical mapping data were assembled by developing a set of computer programs (Integrated Mapping Package) to derive a detailed, annotated map of a 4-Mb region of human chromosome 13 that includes the BRCA2 locus. The final assembly consists of a yeast artificial chromosome (YAC) contig with 42 members spanning the 13q12-13 region and aligned contigs of 399 cosmids established by cross-hybridization between the cosmids, which were selected from a chromosome 13-specific cosmid library using inter-Alu PCR probes from the YACs. The end sequences of 60 cosmids spaced nearly evenly across the map were used to generate sequence-tagged sites (STSs), which were mapped to the YACs by PCR. A contig framework was generated by STS content mapping, and the map was assembled on this scaffold. Additional annotation was provided by 72 expressed sequences and 10 genetic markers that were positioned on the map by hybridization to cosmids.

Direct selection of expressed sequences within a 1-Mb region flanking BRCA1 on human chromosome 17q21

Direct selection of genes within the interval of chromosome 17q21 containing BRCA1 was performed. YAC and cosmid contigs spanning the BRCA1 region were used to select cDNA clones from pools of cDNAs derived from human placenta, HeLa cells, activated T cells, and fetal head. A minimum set of 48 fragments of nonoverlapping cDNAs that unequivocally mapped within a 1-Mb region was identified, although it is not yet known how many of these are derived from the same transcript. DNA sequence analyses revealed that 4 of these cDNAs were derived from known genes (EDH17B2, glucose-6-phosphatase, IAI.3B, and E1AF), 1 is a member of a previously described gene family (HMG-17), and 7 share substantial identity with previously described genes from human or other species. The remainder showed no significant homology to known genes. Limited PCR-based expression profiles of a set of 13 of the genes were performed, and all gave positive results with at least some cDNA sources supporting the contention that they truly represent transcribed sequences. A comparison between genes obtained from this region by direct selection with those obtained by direct screening or exon trapping (see accompanying papers, this issue) revealed that over 90% of the genes identified by exon trapping were represented in the selected material and that at least two additional genes that appear to represent low abundance transcripts with restricted expression profiles were identified by selection but not by other means.

Polymorphic microsatellites and Wilson disease (WD)

Wilson disease (WD), an autosomal recessive disorder of copper metabolism, has been previously mapped to chromosome 13q. Highly informative PCR-based polymorphic microsatellites closely linked to the WD locus (WND) at 13q14.3, as well as sequence-tagged sites for closely linked loci, are described. Two polymorphic microsatellite markers at D13S118 and D13S119 lie within 3 cM of WND. Two others (D13S227 and D13S228) were derived from a yeast artificial chromosome containing D13S31. These were placed on a genetic linkage map of chromosome 13 and were typed in 74 multiplex WD families from a variety of geographic origins (166 affected members). Multipoint analysis provides very high odds that the location of WND is between D13S31/D13S227/D13S228 and D13S59. Previous odds with RFLP-based markers were only 7:1 more likely than any other location. Current odds are 5,000:1. Preclinical testing of three cases of WD by using the highly informative polymorphic microsatellite markers is described. The markers described here ensure that 95% of predictive tests using DNA from both parents and from at least one affected sib will have an accuracy > 99%.

High-density genetic map of the BRCA1 region of chromosome 17q12-q21

To facilitate the positional cloning of the breast-ovarian cancer gene BRCA1, we constructed a high-density genetic map of the 8.3-cM interval between D17S250 and GIP on chromosome 17q12-q21. Markers were mapped by linkage in the CEPH and in extended kindreds in our breast cancer series. The map comprises 33 ordered polymorphisms, including 12 genes and 21 anonymous markers, yielding an average of one polymorphism every 250 kb. Twenty-five of the markers are PCR-based systems. The order of polymorphic genes and markers is cen-D17S250-D17S518-HER2-THRA1-RARA-D17S80 -KRT10-[D17S800-D17S857]-GAS- D17S856-EDH17B-D17S855-D17S859-D17S858-[++ +PPY-D17S78]-D17S183-EPB3-D17S579- D17S509-[D17S508-D17S190 = D17S810]-D17S791-[D17S181 = D17S806]-D17S797- HOX2B-GP3A-[D17S507 = GIP]-qter. BRCA1 lies in the middle of the interval, between THRA1 and D17S183. Markers from this map can be used to determine whether cancer is linked to BRCA1 in families, to evaluate whether tumors have lost heterozygosity at loci in the region, and to identify probes for characterizing chromosomal rearrangements from patients and from tumors.

THRA1 and D17S183 flank an interval of < 4 cM for the breast-ovarian cancer gene (BRCA1) on chromosome 17q21

In order to pinpoint the locale of the gene for early-onset familial breast and ovarian cancer (BRCA1), polymorphisms were developed within the locus for thyroid hormone receptor alpha (THRA1) and for several anonymous sequences at chromosome 17q12-q21. The THRA1 polymorphism is a dinucleotide repeat with 10 alleles and heterozygosity.79. Gene mapping in extended families with inherited, early-onset breast and ovarian cancer indicates that BRCA1 is distal to THRA1 and proximal to D17S183 (SCG43), an interval of < 4 cM. This locale excludes HER2, THRA1, WNT3, HOX2, NGFR, PHB, COLIA1, NME1, and NME2 as candidates for BRCA1 but does not exclude RARA or EDH17B. Resolving the remaining recombination events in these families by new polymorphisms in the THRA1-D17S183 interval will facilitate positional cloning of the breast-ovarian cancer gene on chromosome 17q12-q21.

Microsatellite polymorphism linkage map of human chromosome 13q

Twelve polymorphic (CA)n microsatellites were isolated from a flow-sorted chromosome 13 genomic library. These, and two others that have been previously described, were genotyped in 41 families from the CEPH (Centre d'Etude Polymorphisme Humain, Paris), and a primary linkage map with considerable support for order (odds > 10,000:1) was constructed. Two RFLP-based markers, COL4A1 and D13S52, with heterozygosities above 0.67 and an RFLP-based centromeric marker at D13Z1 were included in this map which extends from 13cen to 13q34. The heterozygosity of all of the PCR-based markers is above 60%. The total map spans a genetic distance of 144 cM, extending from D13Z1 to D13S52 with a single maximum intermarker recombination distance of 35 cM. All other intermarker recombination distances are 18 cM or less. Marker order was confirmed by sublocalizing many of the microsatellite containing clones on a panel of rodent-human somatic cell hybrids with deletions and rearrangements of chromosome 13. One spontaneous new mutation for these 14 (CA)n repeat markers was identified from a total of 8006 gametes, giving an overall observed spontaneous mutation rate of 0.00012 per locus per gamete. An integrated map of chromosome 13q was constructed with the microsatellite markers described here and previously genotyped RFLP-based markers. This sex-average map spans 209 cM with an average distance between unique map locations of 4.5 cM; the maximum intermarker distance was 14 cM.