Long-term differential modulation of genes encoding orexigenic and anorexigenic peptides by leptin delivered by rAAV vector in ob/ob mice. Relationship with body weight change

Caloric Restriction and Hypothalamic Leptin Gene Therapy Have Differential Effects on Energy Partitioning in Adult Female Rats

Dieting is a common but often ineffective long-term strategy for preventing weight gain. Similar to humans, adult rats exhibit progressive weight gain. The adipokine leptin regulates appetite and energy expenditure but hyperleptinemia is associated with leptin resistance. Here, we compared the effects of increasing leptin levels in the hypothalamus using gene therapy with conventional caloric restriction on weight gain, food consumption, serum leptin and adiponectin levels, white adipose tissue, marrow adipose tissue, and bone in nine-month-old female Sprague-Dawley rats. Rats (n = 16) were implanted with a cannula in the 3rd ventricle of the hypothalamus and injected with a recombinant adeno-associated virus, encoding the rat gene for leptin (rAAV-Lep), and maintained on standard rat chow for 18 weeks. A second group (n = 15) was calorically-restricted to match the weight of the rAAV-Lep group. Both approaches prevented weight gain, and no differences in bone were detected. However, calorically-restricted rats consumed 15% less food and had lower brown adipose tissue Ucp-1 mRNA expression than rAAV-Lep rats. Additionally, calorically-restricted rats had higher abdominal white adipose tissue mass, higher serum leptin and adiponectin levels, and higher marrow adiposity. Caloric restriction and hypothalamic leptin gene therapy, while equally effective in preventing weight gain, differ in their effects on energy intake, energy expenditure, adipokine levels, and body composition.

Ectopic Leptin Production by Intraocular Pancreatic Islet Organoids Ameliorates the Metabolic Phenotype of ob/ob Mice

The pancreatic islets of Langerhans consist of endocrine cells that secrete peptide hormones into the blood circulation in response to metabolic stimuli. When transplanted into the anterior chamber of the eye (ACE), pancreatic islets engraft and maintain morphological features of native islets as well as islet-specific vascularization and innervation patterns. In sufficient amounts, intraocular islets are able to maintain glucose homeostasis in diabetic mice. Islet organoids (pseudo-islets), which are formed by self-reassembly of islet cells following disaggregation and genetic manipulation, behave similarly to native islets. Here, we tested the hypothesis that genetically engineered intraocular islet organoids can serve as production sites for leptin. To test this hypothesis, we chose the leptin-deficient ob/ob mouse as a model system, which becomes severely obese, hyperinsulinemic, hyperglycemic, and insulin resistant. We generated a Tet-OFF-based beta-cell-specific adenoviral expression construct for mouse leptin, which allowed efficient transduction of native beta-cells, optical monitoring of leptin expression by co-expressed fluorescent proteins, and the possibility to switch-off leptin expression by treatment with doxycycline. Intraocular transplantation of islet organoids formed from transduced islet cells, which lack functional leptin receptors, to ob/ob mice allowed optical monitoring of leptin expression and ameliorated their metabolic phenotype by improving bodyweight, glucose tolerance, serum insulin, and C-peptide levels.

Leptin, An Adipokine With Central Importance in the Global Obesity Problem

Leptin has central importance in the global obesity and cardiovascular disease problem. Leptin is principally secreted by adipocytes and acts in the hypothalamus to suppress appetite and food intake, increase energy expenditure, and regulate body weight. Based on clinical translation of specific and networked actions, leptin affects the cardiovascular system and may be a marker and driver of cardiometabolic risk factors with interventions that are actionable by cardiologists. Leptin subnetwork analysis demonstrates a statistically significant role for ethnoculturally and socioeconomically appropriate lifestyle intervention in cardiovascular disease. Emergent mechanistic components and potential diagnostic or therapeutic targets include hexokinase 3, urocortins, clusterin, sialic acid-binding immunoglobulin-like lectin 6, C-reactive protein, platelet glycoprotein VI, albumin, pentraxin 3, ghrelin, obestatin prepropeptide, leptin receptor, neuropeptide Y, and corticotropin-releasing factor receptor 1. Emergent associated symptoms include weight change, eating disorders, vascular necrosis, chronic fatigue, and chest pain. Leptin-targeted therapies are reported for lipodystrophy and leptin deficiency, but they are investigational for leptin resistance, obesity, and other chronic diseases.

Association between obesity and asthma - epidemiology, pathophysiology and clinical profile

Obesity is a risk factor for asthma, and obese asthmatics have lower disease control and increased symptom severity. Several putative links have been proposed, including genetics, mechanical restriction of the chest and the intake of corticosteroids. The most consistent evidence, however, comes from studies of cytokines produced by the adipose tissue called adipokines. Adipokine imbalance is associated with both proinflammatory status and asthma. Although reverse causation has been proposed, it is now acknowledged that obesity precedes asthma symptoms. Nevertheless, prenatal origins of both conditions complicate the search for causality. There is a confirmed role of neuro-immune cross-talk mediating obesity-induced asthma, with leptin playing a key role in these processes. Obesity-induced asthma is now considered a distinct asthma phenotype. In fact, it is one of the most important determinants of asthma phenotypes. Two main subphenotypes have been distinguished. The first phenotype, which affects adult women, is characterised by later onset and is more likely to be non-atopic. The childhood obesity-induced asthma phenotype is characterised by primary and predominantly atopic asthma. In obesity-induced asthma, the immune responses are shifted towards T helper (Th) 1 polarisation rather than the typical atopic Th2 immunological profile. Moreover, obese asthmatics might respond differently to environmental triggers. The high cost of treatment of obesity-related asthma, and the burden it causes for the patients and their families call for urgent intervention. Phenotype-specific approaches seem to be crucial for the success of prevention and treatment.

Hypothalamic leptin gene therapy reduces body weight without accelerating age-related bone loss

Excessive weight gain in adults is associated with a variety of negative health outcomes. Unfortunately, dieting, exercise, and pharmacological interventions have had limited long-term success in weight control and can result in detrimental side effects, including accelerating age-related cancellous bone loss. We investigated the efficacy of using hypothalamic leptin gene therapy as an alternative method for reducing weight in skeletally-mature (9 months old) female rats and determined the impact of leptin-induced weight loss on bone mass, density, and microarchitecture, and serum biomarkers of bone turnover (CTx and osteocalcin). Rats were implanted with cannulae in the 3rd ventricle of the hypothalamus and injected with either recombinant adeno-associated virus encoding the gene for rat leptin (rAAV-Leptin, n=7) or a control vector encoding green fluorescent protein (rAAV-GFP, n=10) and sacrificed 18 weeks later. A baseline control group (n=7) was sacrificed at vector administration. rAAV-Leptin-treated rats lost weight (-4±2%) while rAAV-GFP-treated rats gained weight (14±2%) during the study. At study termination, rAAV-Leptin-treated rats weighed 17% less than rAAV-GFP-treated rats and had lower abdominal white adipose tissue weight (-80%), serum leptin (-77%), and serum IGF1 (-34%). Cancellous bone volume fraction in distal femur metaphysis and epiphysis, and in lumbar vertebra tended to be lower (P<0.1) in rAAV-GFP-treated rats (13.5 months old) compared to baseline control rats (9 months old). Significant differences in cancellous bone or biomarkers of bone turnover were not detected between rAAV-Leptin and rAAV-GFP rats. In summary, rAAV-Leptin-treated rats maintained a lower body weight compared to baseline and rAAV-GFP-treated rats with minimal effects on bone mass, density, microarchitecture, or biochemical markers of bone turnover.

Chronic central leptin infusion modulates the glycemia response to insulin administration in male rats through regulation of hepatic glucose metabolism

Leptin and insulin use overlapping signaling mechanisms to modify hepatic glucose metabolism, which is critical in maintaining normal glycemia. We examined the effect of an increase in central leptin and insulin on hepatic glucose metabolism and its influence on serum glucose levels. Chronic leptin infusion increased serum leptin and reduced hepatic SH-phosphotyrosine phosphatase 1, the association of suppressor of cytokine signaling 3 to the insulin receptor in liver and the rise in glycemia induced by central insulin. Leptin also decreased hepatic phosphoenolpyruvate carboxykinase levels and increased insulin's ability to phosphorylate insulin receptor substrate-1, Akt and glycogen synthase kinase on Ser9 and to stimulate glucose transporter 2 and glycogen levels. Peripheral leptin treatment reproduced some of these changes, but to a lesser extent. Our data indicate that leptin increases the hepatic response to a rise in insulin, suggesting that pharmacological manipulation of leptin targets may be of interest for controlling glycemia.

Hypothalamic leptin gene therapy prevents weight gain without long-term detrimental effects on bone in growing and skeletally mature female rats

Hypothalamic leptin gene therapy normalizes the mosaic skeletal phenotype of leptin-deficient ob/ob mice. However, it is not clear whether increased hypothalamic leptin alters bone metabolism in animals already producing the hormone. The objective of this study was to evaluate the long duration effects of recombinant adeno-associated virus-rat leptin (rAAV-Lep) hypothalamic gene therapy on weight gain and bone metabolism in growing and skeletally mature leptin-replete female Sprague-Dawley rats. Rats were either unoperated or implanted with cannulas in the third ventricle of the hypothalamus and injected with either rAAV-Lep or rAAV-GFP (control vector encoding green fluorescent protein) and maintained on standard rat chow fed ad libitum for either 5 or 10 weeks (starting at 3 months of age) or 18 weeks (starting at 9 months of age). Tibias, femurs, or lumbar vertebrae were analyzed by micro-computed tomography and/or histomorphometry. In comparison with age-matched rAAV-GFP rats, rAAV-Lep rats maintained a lower body weight for the duration of studies. At 5 weeks after vector administration, rAAV-Lep rats had lower cancellous bone volume and bone marrow adiposity but higher osteoblast perimeter compared with nonoperated controls. However, these values did not differ between the two groups at 10 weeks after vector administration. Differences in cancellous bone volume and architecture were not detected between the rAAV-Lep and rAAV-GFP groups at either time point. Also, rAAV-Lep had no negative effects on bone in the 9-month-old skeletally mature rats at 18 weeks after vector administration. We hypothesize that the transient reductions in bone mass and bone marrow adiposity at 5 weeks after vector administration were due to hypothalamic surgery. We conclude that increased hypothalamic leptin, sufficient to prevent weight gain, has minimal specific effects (rAAV-Lep versus rAAV-GFP) on bone metabolism in normal female rats.

Leptin gene therapy in the fight against diabetes

IMPORTANCE OF THE FIELD

The incidence of diabetes is increasing worldwide, yet current treatments are not always effective for all patient or disease types.

AREAS COVERED IN THIS REVIEW

Here, we summarize the biologic and clinical roles of leptin in diabetes, and discuss candidate viral vectors that may be employed in the clinical use of central leptin gene therapy for diabetes.

WHAT THE READER WILL GAIN

We discuss how studies on leptin, a regulator of the insulin-glucose axis, have significantly advanced our understanding of the roles of energy homeostasis and insulin resistance in the pathogeneses of metabolic syndrome and diabetes. Recent studies have demonstrated the long-term therapeutic effects of central leptin gene therapy in obesity and diabetes via decreased insulin resistance and increased glucose metabolism. Many of these studies have employed viral vectors, which afford high in vivo gene transduction efficiencies compared with non-viral vectors.

TAKE HOME MESSAGE

Adeno-associated viral vectors are particularly well suited for central leptin gene therapy owing to their low toxicity and ability to drive transgene expression for extended periods.

Pivotal role of leptin-hypothalamus signaling in the etiology of diabetes uncovered by gene therapy: a new therapeutic intervention?

The incidence of diabetes mellitus has soared to epidemic proportion worldwide. The debilitating chronic hyperglycemia is caused by either lack of insulin as in diabetes type 1 or its ineffectiveness as in diabetes type 2. Frequent replacement of insulin with or without insulin analogs for optimum glycemic control are the conventional cumbersome therapies. Recent application of leptin gene transfer technology has uncovered the participation of adipocytes-derived leptin-dependent hypothalamic neural signaling in glucose homeostasis and demonstrated that a breakdown in this communication due to leptin insufficiency in the hypothalamus underlies the etiology of chronic hyperglycemia. Reinstatement of central leptin sufficiency by hyperleptinemia produced either by intravenous leptin infusion or a single systemic injection of recombinant adenovirus vector encoding leptin gene suppressed hyperglycemia and evoked euglycemia only transiently in rodent models of diabetes type 1. In contrast, stable restoration of leptin sufficiency, solely in the hypothalamus, with biologically active leptin transduced by an intracerebroventicular injection of recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) abolished hyperglycemia and imposed euglycemia through the extended duration of experiment by stimulating glucose disposal in the periphery in models of diabetes type 1. Further, similar hypothalamic leptin transgene expression abrogated chronic hyperglycemia and hyperinsulinemia, the predisposing risk factors of the age and environmentally acquired diabetes type 2, and instituted euglycemia by independently activating relays that stimulate glucose metabolism and repress hyperinsulinemia and improve insulin sensitivity in the periphery. Consequently, this durable antidiabetic efficacy of one time rAAV-lep neurotherapy offers a potential novel substitute for insulin therapy following preclinical trials in subhuman primates and humans.

Behavioral and pharmacologic therapies for obesity

This article reviews novel developments in the behavioral and pharmacologic treatment of obesity and explores the potential contribution of genomics research to weight control. A comprehensive program of lifestyle modification, comprised of diet, physical activity and behavior therapy, induces a mean loss of 7-10% of initial weight in individuals with obesity. Two trials demonstrated that weight loss of this magnitude, combined with increased physical activity, substantially reduced the risk of developing type 2 diabetes mellitus in individuals with impaired glucose tolerance. A third trial is now investigating whether lifestyle intervention will reduce cardiovascular morbidity and mortality in overweight individuals who already have diabetes mellitus. Pharmacotherapy is recommended, in some patients, as an adjunct to lifestyle modification. Two medications-orlistat and sibutramine-are currently approved in the US for long-term weight loss. Both are efficacious when combined with lifestyle modification, although health concerns have been raised about the use of sibutramine. Several novel combination therapies, which target multiple hypothalamic pathways that regulate appetite and body weight, are currently under investigation. Genomic studies provide further evidence for the role of these pathways in the regulation of body weight. Identification of new genes controlling satiety and energy expenditure may yield valuable clues for the development of novel pharmacologic treatments.

Central leptin gene therapy ameliorates diabetes type 1 and 2 through two independent hypothalamic relays; a benefit beyond weight and appetite regulation

Although its role in energy homeostasis is firmly established, the evidence accumulated over a decade linking the adipocyte leptin-hypothalamus axis in the pathogenesis of diabetes mellitus has received little attention in the contemporary thinking. In this context various lines of evidence are collated here to show that (1) under the direction of leptin two independent relays emanating from the hypothalamus restrain insulin secretion from the pancreas and mobilize peripheral organs--liver, skeletal muscle and brown adipose tissue--to upregulate glucose disposal, and (2), leptin insufficiency in the hypothalamus produced by either leptinopenia or restriction of leptin transport across the blood brain barrier due to hyperleptinemia of obesity and aging, initiate antecedent pathophysiological sequalae of diabetes type 1 and 2. Further, we document here the efficacy of leptin replenishment in vivo, especially by supplying it to the hypothalamus with the aid of gene therapy, in preventing the antecedent pathophysiological sequalae--hyperinsulinemia, insulin resistance and hyperglycemia--in various animal models and clinical paradigms of diabetes type 1 and 2 with or without attendant obesity. Overall, the new insights on the long-lasting antidiabetic potential of two independent hypothalamic relays engendered by central leptin gene therapy and the preclinical safety indicators in rodents warrant further validation in subhuman primates and humans.

Central leptin gene therapy, a substitute for insulin therapy to ameliorate hyperglycemia and hyperphagia, and promote survival in insulin-deficient diabetic mice

Long-term benefits of central leptin gene therapy in insulin-deficient diabetes are not known despite its therapeutic effects in obesity animal models such as ob/ob and diet-induced obese mice. Adult male mice were injected intraperitoneally with streptozotocin (STZ, 200mg/kg) to induce insulitis. A week later, only diabetic STZ-pretreated mice (blood glucose >350 mg/dl) received intracerebroventricularly (icv) an injection of recombinant adeno-associated virus vector (rAAV) encoding either green fluorescent protein (control), or leptin gene (rAAV-lep). Body weight (BW), food intake, blood glucose, insulin and survival rate responses were monitored post-icv injection at regular intervals for 52 weeks. The STZ pre-injected diabetic mice remained hyperphagic, gradually lost BW and died by week 6 after receiving control vector. In marked contrast, injection of rAAV-lep to raise hypothalamic leptin levels, rescued the STZ-pretreated mice from early mortality, gradually curbed hyperphagia to normalize intake by week 20, and maintained BW at significantly lower than the control range. Blood glucose levels in these mice started to recede dramatically by week 2-3 to normalize by week 8, and euglycemia was sustained during the remaining course of the experiment. rAAV-lep injected mice did not exhibit any discernible untoward gross behavioral changes and diabetic complications and showed a partial return of pancreatic beta-cell function. These results show for the first time that one time central leptin gene therapy is effective and durable in reinstating euglycemia and energy homeostasis for extended periods in the absence of insulin.

Leptin increases osteoblast-specific osteocalcin release through a hypothalamic relay

Enhanced long-term expression of leptin by gene therapy selectively in the hypothalamus, without leakage to the systemic circulation, abrogated skeletal abnormalities and reinstated weight and insulin-glucose homeostasis in leptin-deficient ob/ob mice. Whether increases in osteocalcin, a hormone produced by osteoblasts and known to play a role in bone growth and recently in glucose-insulin homeostasis, may link these benefits of central leptin was assessed. The effects of a single intraventricular injection of non-immunogenic, non-pathogenic recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) or green fluorescent protein gene (rAAV-GFP, control) were studied in three genotypes, wild type (wt), obese diabetic, hyperinsulinemic ob/ob and non-obese, diabetic insulinopenic Akita mice. Selective hypothalamic leptin expression with central rAAV-lep treatment decreased weight, fat mass, food intake, suppressed insulin levels in ob/ob and wt mice, and conferred euglycemia by suppressing blood glucose in all three genotypes. Contemporaneously, rAAV-lep treatment also augmented blood osteocalcin levels. In wt mice, osteocalcin rose by 51% and, whereas, basal osteocalcin levels in ob/ob and Akita mice were significantly lower as compared to those in wt mice (26% and 55%, respectively), gene therapy reinstated levels to the control range in ob/ob mice, and raised 40% above the wt range even in the absence of insulin in Akita mice. These findings demonstrate that the central beneficial effects of leptin on bone growth involve increased hypothalamic relay of signals that augment osteocalcin efflux from osteoblasts into the general circulation, a response that, in turn, may also modulate glucose-insulin and weight homeostasis.

Body mass influences cortical bone mass independent of leptin signaling

Obesity in humans is associated with increased bone mass. Leptin, a hormone produced by fat cells, functions as a sentinel of energy balance, and may mediate the putative positive effects of body mass on bone. We performed studies in male C57Bl/6 wild type (WT) and leptin-deficient ob/ob mice to determine whether body mass gain induced by high fat intake increases bone mass and, if so, whether this requires central leptin signaling. The relationship between body mass and bone mass and architecture was evaluated in 9-week-old and 24-week-old WT mice fed a regular mouse diet. Femora and lumbar vertebrae were analyzed by micro computed tomography. In subsequent studies, slowly and rapidly growing ob/ob mice were injected in the hypothalamus with a recombinant adeno-associated virus containing the leptin gene (rAAV-lep) or a control vector, rAAV-GFP (green fluorescent protein). The mice were maintained on a regular control diet for 5 or 7 weeks and then subdivided into groups and either continued on the control diet or fed a high fat diet (45% of kcal from fat) for 8 weeks. In the WT mice, femoral and vertebral bone mass was positively correlated with body mass (Pearson's r=0.65-0.88 depending on endpoint). rAAV-lep therapy dramatically decreased body mass (-61%) but increased femur length. However, in the distal femur and lumbar vertebra, rAAV-lep therapy reduced cancellous bone volume/tissue volume, trabecular number and trabecular thickness, and increased trabecular spacing. The high fat diet increased body mass, irrespective of vector treatment. Total femur bone volume, length, cross-sectional volume, and cortical volume and thickness were increased in mice with increased body mass, independent of rAAV treatment. In the distal femur, increased body mass had no effect on cancellous architecture and there were no vector x body mass interactions. In WT mice, increased body mass resulted in increased (+33%) vertebral cancellous bone volume/tissue volume. Increased body mass had minimal independent effect on cancellous vertebral bone mass in ob/ob mice. Taken together, these findings suggest that increased body mass has a positive effect on femur cortical bone mass that is independent of leptin signaling.

Disruption in the leptin-NPY link underlies the pandemic of diabetes and metabolic syndrome: new therapeutic approaches

Multidisciplinary research from my and my colleagues' laboratory has shown that disruption at various levels of leptin signaling to the interactive hypothalamic network of neuropeptide Y (NPY) and cohorts contributes to the antecedent pathophysiologic sequelae of the disease cluster of the metabolic syndrome. Disruptions in NPY signaling due to high or low abundance of NPY and cognate receptors dysregulate the homeostatic milieu to promote hyperinsulinemia, hyperglycemia, fat accrual, and overt diabetes. Hyperleptinemia induced by consumption of energy-rich diets inhibits leptin transport across the blood-brain barrier and thereby produces leptin insufficiency in the hypothalamus. Sustained leptin insufficiency results in loss of hypothalamic restraint on pancreatic insulin secretion and diminished glucose metabolism and energy expenditure. This chain of events culminates in hyperinsulinemia, hyperglycemia, and diabetes. Our recent studies have shown that increasing the supply of leptin centrally by gene therapy reinstates the restraint on hypothalamic NPY signaling and ameliorates diabetes and the attendant disease cluster of the metabolic syndrome. Thus, newer therapies that would enhance leptin transport across the blood-brain barrier in a timely manner or reinstate leptin restraint on NPY signaling through central leptin gene therapy or pharmacologically with leptin mimetics are likely to curtail the pathophysiologic sequelae of diabetes and related ailments of the metabolic syndrome.

Increased leptin expression selectively in the hypothalamus suppresses inflammatory markers CRP and IL-6 in leptin-deficient diabetic obese mice

Low-grade systemic inflammation, as indicated by increased circulating levels of inflammatory markers CRP and IL-6, is linked to increased risks for cardiovascular diseases (CVD) and diabetes mellitus in obese subjects. Whereas hyperleptinemia in obesity are associated with increased CRP and IL-6 release, the hypothalamic versus peripheral site of leptin action has not been ascertained. The effects of increased leptin supply selectively in the hypothalamus by gene therapy on pro-inflammatory CRP and IL-6 levels and on markers of diabetes in the circulation of ob/ob mice displaying either age-related or dietary obesity were assessed. A recombinant adeno-associated viral vector encoding either green-fluorescent protein (control) or leptin gene was injected intracerebroventricularly. Five weeks later, one-half of each of the vector groups was switched to high-fat diet consumption and the other half continued to consume regular low-fat chow diet. Body weight and visceral white adipose tissue were drastically reduced and hyperinsulinemia and hyperglycemia were abrogated by leptin gene therapy, independent of the dietary fat content. The elevated plasma CRP and IL-6 levels seen in obese ob/ob mice receiving the control vector, regardless of the fat content of the diet, were markedly suppressed by increased hypothalamic leptin in both groups. The results show for the first time that leptin deficiency elevates and reinstatement of leptin selectively in the hypothalamus suppresses the release of pro-inflammatory biomarkers, a response likely to alleviate CVD associated with obesity.

Central leptin insufficiency syndrome: an interactive etiology for obesity, metabolic and neural diseases and for designing new therapeutic interventions

This review critically reappraises recent scientific evidence concerning central leptin insufficiency versus leptin resistance formulations to explain metabolic and neural disorders resulting from subnormal or defective leptin signaling in various sites in the brain. Research at various fronts to unravel the complexities of the neurobiology of leptin is surveyed to provide a comprehensive account of the neural and metabolic effects of environmentally imposed fluctuations in leptin availability at brain sites and the outcome of newer technology to restore leptin signaling in a site-specific manner. The cumulative new knowledge favors a unified central leptin insufficiency syndrome over the, in vogue, central resistance hypothesis to explain the global adverse impact of deficient leptin signaling in the brain. Furthermore, the leptin insufficiency syndrome delineates a novel role of leptin in the hypothalamus in restraining rhythmic pancreatic insulin secretion while concomitantly enhancing glucose metabolism and non-shivering thermogenic energy expenditure, sequelae that would otherwise promote fat accrual to store excess energy resulting from consumption of energy-enriched diets. A concerted effort should now focus on development of newer technologies for delivery of leptin or leptin mimetics to specifically target neural pathways for remediation of diverse ailments encompassing the central leptin insufficiency syndrome.

Central leptin gene therapy corrects skeletal abnormalities in leptin-deficient ob/ob mice

Skeletal growth is tightly coupled to energy balance via complex and incompletely understood mechanisms. Leptin-deficient ob/ob mice are obese and develop multiple pathologies associated with the metabolic syndrome. Additionally, ob/ob mice have skeletal abnormalities. The objective of this study was to evaluate the effects of leptin deficiency and long duration selective central leptin repletion via recombinant adeno-associated virus-leptin (rAAV-lep) gene therapy on bone in growing ob/ob mice. The ob/ob mice were injected in the hypothalamus with either rAAV-lep or rAAV-GFP (control vector). Treated ob/ob and untreated wild-type (WT) mice were then maintained on a normal diet for 15 weeks. In a second experiment, similarly treated mice along with a group of pair-fed mice were maintained for 30 weeks. Leptin was not detected in blood of either rAAV-lep- or rAAV-GFP-treated mice although rAAV-lep-treated mice displayed leptin transgene expression in the hypothalamus. As expected, rAAV-lep normalized body weight and food intake. Compared to WT mice, rAAV-GFP-treated ob/ob mice had decreased femoral length (by 1.6 mm or 10%, P<0.001), decreased total femur bone volume (by 3.3 mm(3) or 19%, P<0.001), but increased cancellous bone volume in the distal femur (by 0.04 mm(3) or 60%, P<0.09) and lumbar vertebrae (by 0.26 mm(3) or 118%, P<0.001). Treatment with rAAV-lep rescued the ob/ob skeletal phenotype by increasing femoral length and total bone volume, and decreasing femoral and vertebral cancellous bone volume, so that at 15 weeks post-rAAV-lep injection the ob/ob mice no longer differed from WT mice. No further skeletal changes in either the femur or lumbar vertebra were observed at 30 weeks post-rAAV-lep administration. The results suggest that hypothalamic leptin functions as an essential permissive factor for normal bone growth.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

To subjugate NPY is to improve the quality of life and live longer

The interactive network of neuropeptide Y (NPY) and cohorts is necessary for integrating the hypothalamic regulation of appetite and energy expenditure with the endocrine and neuroendocrine systems on a daily basis. Genetic and environmental factors that produce an insufficiency of leptin restraint on NPY and cognate receptors deregulate the homeostasis to engender various life-threatening risk factors. Recent studies from our laboratory show that neurotherapy consisting of a single central administration of recombinant adeno-associated virus vector encoding the leptin gene can repress the hypothalamic NPY system for the lifetime of rodents. A major benefit of this stable tonic restraint is deceleration of pathophysiologic sequalae that shorten life span. These include suppression of weight gain, fat accumulation, circulating adipokines, amelioration of major symptoms of metabolic syndrome, improved reproduction and bone health. Thus, sustained repression of NPY signaling in the hypothalamus by leptin transgene expression can improve the quality of life and extend longevity.

Hypothalamic clamp on insulin release by leptin-transgene expression

The effects of sustained leptin action locally in the hypothalamus on the functional link between fat accrual and insulin secretion after chronic high fat diet (HFD) consumption in leptin-deficient ob/ob mice, and on the post-prandial insulin response in rats consuming regular chow diet (RCD), was examined in this study. A single intracerebroventricular (icv) injection of recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) enhanced hypothalamic leptin-transgene expression in ob/ob mice consuming RCD and suppressed the time-related weight gain and fat accumulation concomitant with abrogation of hyperinsulinemia and enhanced glucose tolerance. This increased hypothalamic leptin-transgene expression continued to impose insulinopenia and increased glucose tolerance but was ineffective in suppressing weight gain and fat accumulation after these mice were switched to chronic HFD consumption. A similar icv rAAV-lep pretreatment in rats consuming RCD markedly attenuated the post-prandial rise in insulin release concomitant with suppressed weight and fat depots. These results show for the first time that a sustained hypothalamic leptin action can stably clamp pancreatic insulin secretion independent of the status of fat accrual engendered by diets of varying caloric enrichment. Thus, the efficacy of increased leptin afferent signaling in the hypothalamus to persistently restrain pancreatic insulin release and insulin resistance can be explored as an adjunct therapeutic modality to alleviate pathophysiological derrangements that confer type 2 diabetes.

Leptin gene transfer in the hypothalamus enhances longevity in adult monogenic mutant mice in the absence of circulating leptin

Leptin, a product of the ob gene, is a pleiotropic signal implicated in regulation of multiple physiological functions in the periphery and centrally, including hypothalamic integration of energy homeostasis. Recessive mutations of ob gene result in early onset of hyperphagia, morbid obesity, metabolic disorders, early mortality and shortened life-span. Intracerebroventricular injection of recombinant adeno-associated virus vector (rAAV) encoding the leptin gene in adult obese ob/ob mice enhanced leptin transgene expression only in the hypothalamus, normalized food intake, body weight and more than doubled the life-span as compared to control cohorts and extended it to near that of normal wild type mice. These life-extending benefits were associated with drastic reductions in visceral fat, and blood glucose and insulin levels, but elevated ghrelin levels, the anti-aging biomarkers. Thus, bioavailability of leptin transduced by ectopic gene in the hypothalamus alone is both necessary and sufficient to normalize life-span. Evidently, site-specific ectopic gene expression with rAAV is durable and safe for alleviating neural disorders that stem from missing or functional disruption of a single gene.

Leptin transgene expression in the hypothalamus enforces euglycemia in diabetic, insulin-deficient nonobese Akita mice and leptin-deficient obese ob/ob mice

We have tested the hypothesis that sustained leptin action in the hypothalamus alone can engender and maintain euglycemia in wild type mice and in two monogenic diabetic models, the insulin-deficient nonobese Akita mice and the hyperinsulinemic leptin-deficient obese, ob/ob mice. A single intracerebroventricular injection of recombinant adeno-associated virus vector encoding leptin (rAAV-lep) enhanced leptin transgene expression in the hypothalamus without any evidence of leptin leakage to the peripheral circulation, and promptly reinstated euglycemia that persisted along with severe insulinopenia in all three genotypes through the 7-week period of observation. A comparative evaluation of known etiologic factors of hyperglycemia showed that this long-term benefit on glucose homeostasis was not due to diminished energy consumption, weight and adiposity, but was conferred by at least two mechanisms operating simultaneously, enhanced glucose metabolism to meet the demand for the rAAV-lep induced increased non-shivering thermogenesis mediated by brown adipose tissue and insulin hypersensitivity. These findings endorse the hypothesis that increased leptin action locally in the hypothalamus can impose euglycemia independent of pancreatic insulin, and central leptin reinforcement may serve as a newer adjunct therapy to treat type 1 and type 2 diabetes.

Subjugation of hypothalamic NPY and cohorts with central leptin gene therapy alleviates dyslipidemia, insulin resistance, and obesity for life-time

An interactive network comprised of neuropeptide Y (NPY) and cohorts is obligatory in the hypothalamic integration of appetite and energy expenditure on a minute-to-minute basis. High or low abundance of NPY and cognate receptors dysregulates the homeostatic milieu engendering hyperphagia, decreased energy expenditure, obesity and attendant metabolic syndrome cluster of dyslipidemia, glucose intolerance, insulin resistance and hyperinsulinemia, risk factors for type II diabetes and cardiovascular diseases. Increasing the supply of the endogenous repressor hormone leptin locally in the hypothalamus with the aid of leptin gene therapy, blocked age-related and dietary obesities, and the sequential development of dyslipidemia, hyperglycemia, and insulin resistance. Thus, sustained repression of NPY signaling with increased leptin selectively in the hypothalamus can avert environmental obesity and the risks of metabolic diseases.

Central leptin differentially modulates ultradian secretory patterns of insulin, leptin and ghrelin independent of effects on food intake and body weight

We tested the hypothesis that leptin acts centrally to differentially modulate the ultradian communication of leptin, insulin and ghrelin with the hypothalamus. The ultradian fluctuation of these hormones in plasma after central leptin gene therapy was analyzed. Increased leptin transgene expression in the hypothalamus significantly decreased energy intake and body weight concomitant with severe hypoleptinemia and hypoinsulinemia resulting from drastically suppressed peak heights with unchanged frequency discharge of these hormones. Ghrelin secretion was, however, increased solely due to increased pulse amplitude. In pair-fed control rats leptin and ghrelin secretion was unchanged. In conclusion, independent of restraint on caloric intake and weight, leptin acting centrally modulates only the pulse amplitude of ultradian rhythmicity of the three afferent signals involved in the hypothalamic integration of energy balance. Since rhythmic discharge patterns dictate target response of hormones, these findings reveal a novel hypothalamic action of leptin in the pathophysiology of the obesity-dependent metabolic syndrome.

AAV-mediated leptin receptor installation improves energy balance and the reproductive status of obese female Koletsky rats

Leptin is a hormone secreted primarily by white adipocytes that regulates energy homeostasis and reproduction via CNS receptors. Koletsky (f/f) rats with a leptin receptor (OB-Rb) gene mutation are obese, diabetic and infertile. We employed recombinant adeno-associated viral (rAAV) vectors to transfer the human OB-Rb gene into the brains of female Koletsky rats to identify sites of leptin action in the brain. rAAV-OB-Rb was microinjected into the medial preoptic area (MPOA), the paraventricular nucleus (PVN), the ventromedial hypothalamus, the arcuate nucleus (ARC), or the dorsal vagal complex in the brainstem. Food intake and body weight were monitored bi-weekly for 55 days. Vaginal cytology was examined daily to assess estrous cyclicity. After sacrifice, uncoupling protein-1 (UCP-1) mRNA in brown adipose tissue and serum concentrations of leptin, insulin, glucose, estradiol and progesterone were measured. Expression of OB-Rb was documented by RT-PCR and site specificity of microinjection was verified by immunohistochemical detection of green fluorescent protein following a control microinjection of rAAV-GFP. OB-Rb installation in the ARC reduced food intake, however, energy expenditure, assessed by UCP-1 mRNA expression, was increased by OB-Rb installation in all sites except the PVN. When injected into the MPOA and ARC, rAAV-OB-Rb stimulated the reproductive axis as evidenced by normalization of estrous cycle length and increased luteinizing hormone releasing hormone concentrations in the hypothalamus. These studies show that long-term installation of a functional leptin receptor in the CNS is achievable using rAAV vectors and further show that leptin acts on specific sites in the brain to produce differential effects on food intake, energy expenditure and reproduction.

Gene-transfer technology: a preventive neurotherapy to curb obesity, ameliorate metabolic syndrome and extend life expectancy

Leptin insufficiency at crucial target sites in the hypothalamic circuitries that integrate energy intake and expenditure underlies abnormal rates of fat accumulation. The payload of this "fat burden" is metabolic syndrome, a cluster of life-threatening metabolic afflictions, and a shorter lifespan. Currently available therapies employed to combat obesity have disadvantages such as poor compliance for lifestyle modification or transient effectiveness and undesirable side-effects of pharmacological interventions. Recent studies suggest that neurotherapy comprising a single central administration of recombinant adeno-associated virus vector encoding the leptin gene severely depletes fat and ameliorates the major symptoms of metabolic syndrome for extended periods in rodents. These persistent benefits avert the deleterious impact of the "fat burden" and extend life expectancy. Thus, the novel approach of central gene-transfer technology has distinct advantages over current therapies and has the potential to correct or slow the progression of inherited or acquired hypothalamic diseases.

High-fat diet-induced ultradian leptin and insulin hypersecretion are absent in obesity-resistant rats

OBJECTIVE

Sprague-Dawley rats fed a high-fat diet (HFD) are either obesity prone (OP) or obesity resistant (OR). We tested the hypothesis that differences in the ultradian rhythmic patterns of insulin and ghrelin in OP vs. OR rats promote obesity in OP rats.

RESEARCH METHODS AND PROCEDURES

Rats were fed regular chow or an HFD, and ultradian fluctuations in leptin, insulin, and ghrelin were analyzed in blood samples collected at 5-minute intervals from intrajugular cannulae of freely moving rats.

RESULTS

Regular chow feeding resulted in a slow weight gain accompanied by small increases in insulin and leptin and a decrease in ghrelin discharge, with only the pulse amplitude significantly altered. Similar changes were observed in OR rats, despite HFD consumption. In contrast, OP rats exhibited a high rate of weight gain and marked hyperinsulinemia, hyperleptinemia, and hypoghrelinemia; amplitude was altered, but frequency was stable. In a short-term experiment, HFD elicited similar secretory patterns of smaller magnitude even in the absence of weight gain.

DISCUSSION

We showed that three hormonal signals of disparate origin involved in energy homeostasis were secreted in discrete episodes, and only the pulse amplitude component was vulnerable to age and HFD consumption. Increases in insulin and leptin and decreases in ghrelin pulse amplitude caused by HFD were exaggerated in OP rats relative to OR rats and preceded the weight increase. These findings show that a distinct genetic predisposition in the endocrine organs of OR rats confers protection against high-fat intake-induced ultradian hypersecretion of obesity-promoting hormonal signals.

Suppression of fat deposition for the life time with gene therapy

Unexpended energy is stored as fat in the body and increased rate of fat accretion culminates in obesity. Obesity increases the risks of many diseases several folds and shortens life span. A progressive deficit in the central feedback effects of leptin, a peptide produced by fat cells and hypothalamus, results in increased weight gain and obesity. This article summarizes our experimental findings to show that a stable increase in leptin availability in the hypothalamus alone with the aid of leptin gene therapy suppresses fat accretion and metabolic hormones for nearly the lifetime of laboratory rodents. Consequently, central leptin gene therapy is a novel modality that offers a viable therapeutic option to reduce fat depots and attendant metabolic sequelae implicated in obesity-related illnesses.

Stimulation of appetite by ghrelin is regulated by leptin restraint: peripheral and central sites of action

A reciprocal rhythmic pattern of 2 afferent hormonal signals, anorexigenic leptin and orexigenic ghrelin, imparts rhythmicity to the neuropeptide Y (NPY) system, the final common pathway for appetite expression in the hypothalamus. We now show that leptin inhibits both the secretion of gastric ghrelin and the stimulation of feeding by ghrelin. We propose that this dual leptin restraint is the major regulatory arm of the feedback communication between the periphery and the hypothalamus for weight homeostasis, and disruption in the rhythmic communication at any locus in the leptin-ghrelin-NPY feedback loop impels loss of hypothalamic control, leading to abnormal weight gain and obesity.

Leptin expression in hypothalamic PVN reverses dietary obesity and hyperinsulinemia but stimulates ghrelin

OBJECTIVE

In order to circumvent the multiple peripheral effects of hyperleptinemia and leptin resistance, the efficacy of leptin transgene expression in the hypothalamic paraventricular nucleus (PVN) to reinstate the central energy homeostasis in obesity was examined.

RESEARCH METHODS AND PROCEDURES

A recombinant adeno-associated viral vector encoding either leptin (rAAV-lep) or green fluorescent protein (rAAV-GFP) was microinjected into the PVN of obesity-prone rats consuming a high-fat diet (HFD).

RESULTS

rAAV-lep, and not rAAV-GFP, microinjection significantly reduced energy intake and enhanced energy expenditure, thereby resulting in normalization of weight and blood levels of leptin, insulin, free fatty acids, and glucose concomitant with enhanced ghrelin secretion during the extended period of observation.

DISCUSSION

Thus, we show, for the first time, that amelioration of leptin insufficiency with enhanced localized leptin availability in the PVN alone can reverse dietary obesity and the attendant hyperinsulinemia and concurrently block the central stimulatory effects of elevated endogenous ghrelin on food intake and adiposity.

Age-dependent hypothalamic expression of neuropeptides in wild-type and melanocortin-4 receptor-deficient mice

In young (35- to 56-day-old) and middle-aged (9-mo-old) wild-type (+/+) and melanocortin-4 receptor (MC4R)-deficient (+/−, −/−) mice, expressions of neuropeptide Y (NPY), agouti-related protein (AGRP), pro-opiomelanocortin (POMC), and cocaine-and-amphetamine-regulated transcript (CART) were analyzed in the arcuate nucleus (ARC) and adjacent regions comprising the dorsomedial (DMN) and ventromedial (VMN) nucleus. In the ARC of young mice, NPY and AGRP expression increased and POMC and CART expression decreased with body fat content. Adjusting for the influence of body fat content by ANCOVA showed that the levels of NPY, POMC, and CART were highest and of AGRP lowest in young −/− mice. In the middle-aged mice, feedback from body fat content was weakened. For −/− mice ANCOVA revealed higher NPY and AGRP, lower POMC, and unchanged CART expression levels relative to young −/− mice. In the DMN and VMN, POMC and AGRP signals were absent at each age. CART was expressed in the DMN independent of age, fat content, and genotype. For NPY expression, an age-dependent induction was found in the DMN and VMN; it was absent in the young but present in the middle-aged mice, showing close positive correlations between body fat content and the numbers of NPY-labeled cells which were further enhanced in −/− mice. Thus MC4R deficiency augments age-induced NPY expression in the DMN and VMN with no feedback from body fat content. Negative feedback control by body fat content on ARC neuropeptide expression is present in young animals but vanishes with age and is modulated by MC4R deficiency.

Hypothalamic levels of NPY, MCH, and prepro-orexin mRNA during pregnancy and lactation in the rat: role of prolactin

Pregnancy and lactation provide excellent models of physiological hyperphagia and hyperprolactinemia. To identify possible factors associated with the increased feeding in these situations, we measured hypothalamic mRNA levels of three orexigenic neuropeptides--NPY, MCH, and orexins--in nonpregnant, pregnant, and lactating rats by in situ hybridization. NPY mRNA content in the arcuate nucleus was significantly increased during pregnancy and lactation. However, MCH and prepro-orexin expression was decreased in both states. 48 or 72 h of fasting in pregnant and lactating rats further elevated NPY mRNA levels and increased the low MCH mRNA content. Surprisingly, no effect was observed in prepro-orexin mRNA levels. Finally, we investigated the possible effect of high PRL levels on these orexigenic signals using a model of hyperprolactinemia induced by pituitary graft. NPY mRNA content was unchanged, but MCH and prepro-orexin mRNA levels were significantly decreased. Our results suggest that the increased NPY expression might be partly responsible for the hyperphagia observed during pregnancy and lactation. MCH and prepro-orexin may be involved in the adaptation of other homeostatic mechanisms and their decreased levels in these physiological settings could be mediated by the elevated circulating PRL levels.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

Long-term suppression of weight gain, adiposity, and serum insulin by central leptin gene therapy in prepubertal rats: effects on serum ghrelin and appetite-regulating genes

Intracerebroventricular administration of recombinant adeno-associated virus (rAAV) encoding the rat leptin gene (rAAV-lep) to 24-d-old female and male rats suppressed postpubertal weight gain for extended periods by decreasing food consumption and adiposity, as reflected by lowered serum leptin, insulin, and FFA. Serum ghrelin levels were increased in young but not older rats. Central rAAV-lep therapy also increased energy expenditure through nonshivering thermogenesis in younger rats as shown by expression of uncoupling protein mRNA in brown adipose tissue. The sustained decrease in appetite seemingly resulted from attenuation of appetite-stimulating neuropeptide Y and enhancement of appetite-inhibiting melanocortin signalings in the hypothalamus. Neither the onset of pubertal sexual maturation nor reproductive cyclicity in adult female rats was affected by the sustained reduction in energy consumption and weight gain. These findings demonstrate that central leptin gene therapy in prepubertal rats is a novel therapy to control postpubertal weight gain, adiposity, and hyperinsulinemia for extended periods.

CART promoter CRE site binds phosphorylated CREB

It has been shown previously that: CART (cocaine- and amphetamine-regulated transcript) mRNA is tightly regulated in brain; protein kinase A (PKA) is involved in CART expression in GH3 cells; and a cyclic AMP-responsive element (CRE) site is present in the proximal promoter region of the CART gene. Thus, the goal of this study was to test if CRE binding protein (CREB) can bind to the consensus CRE site and if phosphorylation of CREB occurs in GH3 cells under conditions of enhanced CART gene expression. Electromobility shift assays showed that a 27-bp oligonucleotide containing the CART CRE site was indeed bound by nuclear factors. Western blotting showed that incubation of GH3 cells with forskolin, which enhances CART mRNA expression, caused an increase in phosphorylated CREB (P-CREB) levels. Supershift analyses indicated that the CART CRE oligo/protein complex interacted with a P-CREB antibody. Taken together, these data indicate that P-CREB is a likely regulator of CART expression in GH3 cells.

Corticostriatopallidal neuroprotection by adenovirus-mediated ciliary neurotrophic factor gene transfer in a rat model of progressive striatal degeneration

Ciliary neurotrophic factor (CNTF) is a potent protective factor for striatal neurons in animal models of Huntington's disease (HD). Clinical application of this potential therapeutic still requires the design and optimization of delivery systems. In the case of HD, spatial spread in the vast volume occupied by the striatum and long-term delivery of the factor are particular challenges for these systems. We explored the potential of adenovirus-mediated gene transfer to fulfill these requirements by studying the functional and anatomical effects of single-site striatal delivery of CNTF recombinant vectors in a rat model of HD. In an initial series of experiments, unilateral injections of CNTF adenovirus were performed in rats 10, 30, or 90 d before a 5 d neurotoxic treatment with systemic 3-nitropropionic acid (3NP). Preservation of striatal neurons was observed at all time points, demonstrating temporally extended neuroprotective effects of the CNTF adenovirus. In a second series of experiments, bilateral injections of CNTF adenovirus were performed in the medial aspect of the striatum 10 d before starting 3NP intoxication. Despite placement of the CNTF-producing vector outside the lateral striatal area susceptible to lesion, massive protection of corticostriatopallidal circuits was observed, associated with significant behavioral benefits. This spatial spread of neuroprotection is discussed with reference to the retrograde transport of the adenovirus vector and the anterograde transport of the transgenic CNTF. Overall, adenovirus-mediated CNTF gene transfer appears to be a potentially useful delivery system for widespread, long-term circuit neuroprotection in HD patients.

[Leptin-induced regulation of fat metabolism and its accumulation]

Recent findings have shown that supplementation of leptin decreases body weight in leptin-deficient ob/ob mice through its suppressive effect on food intake and accelerating effect on energy expenditure, particularly on peripheral fat lipolysis. When endogenously hyperleptinemic obese rats were further induced to be hyperleptinemic exogeously using adenovirus vector, their body fat mass was reduced but not food intake. These findings implicate a direct lipolytic action of leptin on peripheral adipose tissues in obese rats because leptin transport capacity across the blood-brain barrier is almost saturated by the relative hyperleptinemia. Recovery from excessive body fat accumulation after adenovirus-induced hyperleptinemia is much slower than that after caloric restriction because there may be difference between those treatments in decreased lipogenic enzymes activities and/or increased activities of fatty acid oxidative enzymes and thermogenic uncoupling proteins. The fat melting effects of leptin may show its crucial pharmacologic potencies to design therapeutic strategies against morbid obesity. The studies on leptin provide a better understanding for creative approaches to anti-obesity drug that are efficient for reducing body fat mass without harmful side-effects.

Dose-dependent effects of central leptin gene therapy on genes that regulate body weight and appetite in the hypothalamus

We have examined the dose-dependent effects and central action of intraventricular administration of a recombinant adeno-associated virus encoding rat leptin (rAAV-leptin) in suppressing body weight (BW) gain in adult female rats. A low dose of rAAV-leptin (5x10(10) particles) suppressed weight gain (15%) without changing daily food intake (FI), but a twofold higher dose decreased BW by 30% along with a reduction in daily FI. Reduced BW was due to a loss in body adiposity because serum leptin was reduced. Serum insulin levels were decreased (96%) by only the high dose along with a slight reduction in glucose. Uncoupling protein-1 (UCP-1) mRNA expression in brown adipose tissue (BAT), reflecting energy expenditure through thermogenesis, was upregulated to the same magnitude by the two rAAV-leptin doses. We analyzed by in situ hybridization the expression in the hypothalamus of genes encoding the appetite-regulating neuropeptides. Only the high dose decreased expression of neuropeptide Y (NPY), the orexigenic peptide, and increased proopiomelanocortin (POMC), precursor of the an orexigenic peptide, alpha-MSH. Our studies show for the first time that increased availability of leptin within the hypothalamus through central leptin gene therapy dose-dependently decreases weight gain, adiposity, and serum insulin by increasing energy expenditure and decreasing FI. The decrease in FI occurs only when NPY is reduced and alpha-MSH is increased in the hypothalamus by the high dose of rAAV-leptin. Delivery of the leptin gene centrally through rAAV vectors is a viable therapeutic modality for long-term control of weight and metabolic hormones.

Central leptin gene therapy suppresses body weight gain, adiposity and serum insulin without affecting food consumption in normal rats: a long-term study

The weight-reducing effects of leptin are predominantly mediated through the hypothalamus in the brain. Gene therapy strategies designed for weight control have so far tested the short-term effect of peripherally delivered viral vectors encoding the leptin gene. In order to circumvent the multiple peripheral effects of hyperleptinemia and to overcome the age-related development of leptin resistance due to multiple factors, including defective leptin transport across the blood brain barrier, we determined whether delivery of viral vectors directly into the brain is a viable therapeutic strategy for long-term weight control in normal wild-type rats. A recombinant adeno-associated virus (rAAV) vector encoding rat leptin (Ob) cDNA was generated (rAAV-betaOb). When administered once intracerebroventricularly (i.c.v.), rAAV-betaOb suppressed the normal time-related weight gain for extended periods of time in adult Sprague-Dawley rats. The vector expression was confirmed by immunocytochemical localization of GFP and RT-PCR analysis of leptin in the hypothalamus. This sustained restraint on weight gain was not due to shifts in caloric consumption because food-intake was similar in rAAV-betaOb-treated and rAAV-GFP-treated control rats throughout the experiment. Weight gain suppression, first apparent after 2 weeks, was a result of reduced white fat depots and was accompanied by drastically reduced serum leptin and insulin concentrations in conjunction with normoglycemia. Additionally, there was a marked increase in uncoupling protein-1 (UCP1) mRNA expression in brown adipose tissue, thereby indicating increased energy expenditure through thermogenesis. Seemingly, a selective enhancement in energy expenditure following central delivery of the leptin gene is a viable therapeutic strategy to control the age-related weight gain and provide protection from the accompanying multiple peripheral effects of hyperleptinemia and hyperinsulinemia.