STEMIN and YAP5SA synthetic modified mRNAs regenerate and repair infarcted mouse hearts

Introduction

The adult heart lacks the regenerative capacity to self-repair. Serum response factor (SRF) is essential for heart organogenesis, sarcomerogenesis, and contractility. SRF interacts with co-factors, such as NKX2.5 and GATA4, required for cardiac specified gene activity. ETS factors such as ELK1 interact with SRF and drive cell replication. To weaken SRF interactions with NKX2.5 and GATA4, one mutant, SRF153(A3) named STEMIN, did not bind CArG boxes, yet induced stem cell factors such as NANOG and OCT4, cardiomyocyte dedifferentiation, and cell cycle reentry. The mutant YAP5SA of the Hippo pathway also promotes cardiomyocyte proliferation and growth.

Aim

Infarcted adult mouse hearts were injected with translatable STEMIN and YAP5SA mmRNA to evaluate their clinical potential.

Methods and Results

Mice were pulsed one day later with alpha-EDU and then heart sections were DAPI stained. Replicating cells were identified by immuno-staining against members of the DNA replisome pathway that mark entry to S phase of the cell cycle. Echocardiography was used to determine cardiac function following infarcts and mRNA treatment. To monitor cardiac wall repair, microscopic analysis was performed, and the extent of myocardial fibrosis was analyzed for immune cell infiltration. Injections of STEMIN and YAP5SA mmRNA into the left ventricles of infarcted adult mice promoted a greater than 17-fold increase in the DAPI stained and alpha-EDU marked cardiomyocyte nuclei, within a day. We observed de novo expression of phospho-histone H3, ORC2, MCM2, and CLASPIN. Cardiac function was significantly improved by four weeks post-infarct, and fibrosis and immune cell infiltration were diminished in hearts treated with STEMIN and YAP5SA mmRNA than each alone.

Conclusion

STEMIN and YAP5SA mmRNA improved cardiac function and myocardial fibrosis in left ventricles of infarcted adult mice. The combinatorial use of mmRNA encoding STEMIN and YAP5SA has the potential to become a powerful clinical strategy to treat human heart disease.

HIV-1 Viral Protein R Couples Metabolic Inflexibility With White Adipose Tissue Thermogenesis

Persons living with HIV (PLWH) manifest chronic disorders of brown and white adipose tissues that lead to diabetes and metabolic syndrome. The mechanisms that link viral factors to defective adipose tissue function and abnormal energy balance in PLWH remain incompletely understood. Here, we explored how the HIV accessory protein viral protein R (Vpr) contributes to adaptive thermogenesis in two mouse models and human adipose tissues. Uncoupling protein 1 (UCP1) gene expression was strongly increased in subcutaneous white adipose tissue (WAT) biopsy specimens from PLWH and in subcutaneous WAT of the Vpr mice, with nearly equivalent mRNA copy number. Histology and functional studies confirmed beige transformation in subcutaneous but not visceral WAT in the Vpr mice. Measurements of energy balance indicated Vpr mice displayed metabolic inflexibility and could not shift efficiently from carbohydrate to fat metabolism during day-night cycles. Furthermore, Vpr mice showed a marked inability to defend body temperature when exposed to 4°C. Importantly, Vpr couples higher tissue catecholamine levels with UCP1 expression independent of β-adrenergic receptors. Our data reveal surprising deficits of adaptive thermogenesis that drive metabolic inefficiency in HIV-1 Vpr mouse models, providing an expanded role for viral factors in the pathogenesis of metabolic disorders in PLWH.

β-Adrenergic stimuli and rotating suspension culture enhance conversion of human adipogenic mesenchymal stem cells into highly conductive cardiac progenitors

Clinical trials using human adipogenic mesenchymal stem cells (hAdMSCs) for the treatment of cardiac diseases have shown improvement in cardiac function and were proven safe. However, hAdMSCs do not convert efficiently into cardiomyocytes (CMs) or vasculature. Thus, reprogramming hAdMSCs into myocyte progenitors may fare better in future investigations. To reprogramme hAdMSCs into electrically conductive cardiac progenitor cells, we pioneered a three-step reprogramming strategy that uses proven MESP1/ETS2 transcription factors, β-adrenergic and hypoxic signalling induced in three-dimensional (3D) cardiospheres. In Stage 1, ETS2 and MESP1 activated NNKX2.5, TBX5, MEF2C, dHAND, and GATA4 during the conversion of hAdMSCs into cardiac progenitor cells. Next, in Stage 2, β2AR activation repositioned cardiac progenitors into de novo immature conductive cardiac cells, along with the appearance of RYR2, CAV2.1, CAV3.1, NAV1.5, SERCA2, and CX45 gene transcripts and displayed action potentials. In Stage 3, electrical conduction that was fostered by 3D cardiospheres formed in a Synthecon®, Inc. rotating bioreactor induced the appearance of hypoxic genes: HIF-1α/β, PCG 1α/β, and NOS2, which coincided with the robust activation of adult contractile genes including MLC2v, TNNT2, and TNNI3, ion channel genes, and the appearance of hyperpolarization-activated and cyclic nucleotide-gated channels (HCN1-4). Conduction velocities doubled to ~200 mm/s after hypoxia and doubled yet again after dissociation of the 3D cell clusters to ~400 mm/s. By comparison, normal conduction velocities within working ventricular myocytes in the whole heart range from 0.5 to 1 m/s. Epinephrine stimulation of stage 3 cardiac cells in patches resulted in an increase in amplitude of the electrical wave, indicative of conductive cardiac cells. Our efficient protocol that converted hAdMSCs into highly conductive cardiac progenitors demonstrated the potential utilization of stage 3 cells for tissue engineering applications for cardiac repair.

Conversion of human cardiac progenitor cells into cardiac pacemaker-like cells

We used a screening strategy to test for reprogramming factors for the conversion of human cardiac progenitor cells (CPCs) into Pacemaker-like cells. Human transcription factors SHOX2, TBX3, TBX5, TBX18, and the channel protein HCN2, were transiently induced as single factors and in trio combinations into CPCs, first transduced with the connexin 30.2 (CX30.2) mCherry reporter. Following screens for reporter CX30.2 mCherry gene activation and FACS enrichment, we observed the definitive expression of many pacemaker specific genes; including, CX30.2, KCNN4, HCN4, HCN3, HCN1, and SCN3b. These findings suggest that the SHOX2, HCN2, and TBX5 (SHT5) combination of transcription factors is a much better candidate in driving the CPCs into Pacemaker-like cells than other combinations and single transcription factors. Additionally, single-cell RNA sequencing of SHT5 mCherry+ cells revealed cellular enrichment of pacemaker specific genes including TBX3, KCNN4, CX30.2, and BMP2, as well as pacemaker specific potassium and calcium channels (KCND2, KCNK2, and CACNB1). In addition, similar to human and mouse sinoatrial node (SAN) studies, we also observed the down-regulation of NKX2.5. Patch-clamp recordings of the converted Pacemaker-like cells exhibited HCN currents demonstrated the functional characteristic of pacemaker cells. These studies will facilitate the development of an optimal Pacemaker-like cell-based therapy within failing hearts through the recovery of SAN dysfunction.

Arginine Metabolism Is Altered in Adults with A-β + Ketosis-Prone Diabetes

Background

A-β + ketosis-prone diabetes (KPD) is a subset of type 2 diabetes in which patients have severe but reversible β cell dysfunction of unknown etiology. Plasma metabolomic analysis indicates that abnormal arginine metabolism may be involved.

Objective

The objective of this study was to determine the relation between gut microbiome and arginine metabolism and the relation between arginine availability and β cell function in KPD patients compared with control participants.

Methods

Kinetics of arginine and related metabolites were measured with stable isotope tracers, and insulin secretory responses to arginine and glucose were determined under euglycemic and hyperglycemic conditions in 6 KPD patients and 6 age-, gender-, and body mass index-matched control participants. Glucose potentiation of arginine-induced insulin secretion was performed in a different set of 6 KPD and 3 control participants.

Results

Arginine availability was higher in KPD patients during euglycemia [53.5 ± 4.3 (mean ± SEM) compared with 40.3 ± 2.4 μmol · kg lean body mass (LBM)-1 · h-1, P = 0.03] but declined more in response to hyperglycemia (Δ 10.15 ± 2.6 compared with Δ 3.20 ± 1.3 μmol · kg LBM-1 · h-1, P = 0.041). During hyperglycemia, ornithine flux was not different between groups but after an arginine bolus, plasma ornithine AUC trended higher in KPD patients (3360 ± 294 compared with 2584 ± 259 min · μmol · L-1, P = 0.08). In both euglycemia and hyperglycemia, the first-phase insulin responses to glucose stimulation were lower in KPD patients (euglycemic insulin AUC 282 ± 108 compared with 926 ± 257 min · μU · mL-1, P = 0.02; hyperglycemic insulin AUC 358 ± 79 compared with 866 ± 292 min · μU · mL-1, P = 0.05), but exogenous arginine restored first-phase insulin secretion in KPD patients to the level of control participants.

Conclusion

Compared with control participants, KPD patients have increased arginine availability in the euglycemic state, indicating a higher requirement. This is compromised during hyperglycemia, with an inadequate supply of arginine to sustain metabolic functions such as insulin secretion. Exogenous arginine administration restores a normal insulin secretory response.

Factors associated with early relapse to insulin dependence in unprovoked A-β+ ketosis-prone diabetes

OBJECTIVE

Unprovoked "A-β+" Ketosis-Prone Diabetes (KPD), a unique diabetic syndrome of adult-onset, obesity and proneness to ketoacidosis, is associated with rapid recovery of β cell function and insulin-independence. Whereas most patients experience prolonged remission, a subset relapses early to insulin dependence. We sought to define factors associated with early relapse.

METHODS

We utilized a prospective, longitudinal database to analyze 50 unprovoked A-β+ KPD patients with >2 measurements of β cell function and glycemia following baseline assessment.

RESULTS

19 patients (38%) relapsed to insulin dependence <1 year after the index DKA episode, while 31 (62%) remained insulin-independent for >1 year (median 4.2 years). Younger age at baseline (OR=0.947, P=0.033), and lower HOMA2-%β (OR=0.982, P=0.001), lower HOMA2-IR (OR=0.582, P=0.046) and higher HbA1c at 1 year (OR=1.71, P=0.002) were associated with early relapse. A multivariate model with these variables and the interaction of HOMA2-%β and HbA1c at 1 year provided a good fit (P<0.05).

CONCLUSIONS

Relapse to insulin dependence in unprovoked A-β+ KPD patients is associated with younger age and, after 1 year, lack of robust increase in β cell functional reserve, and suboptimal glycemic control. Measurements of these parameters 1 year after the index DKA episode can be used to assess the need for insulin therapy.

Early screening to identify patients at risk of developing intra-abdominal hypertension and abdominal compartment syndrome

BACKGROUND

To develop a screening tool to identify patients at risk of developing intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) within 24 h of a patient's admission to intensive care unit (ICU).

METHODS

Prospective, observational study of 403 consecutively enrolled patients with an indwelling catheter, admitted to a mixed medical-surgical ICU in a tertiary referral, university hospital. Intra-abdominal pressure was measured at least twice daily and IAH and ACS defined as per consensus definitions.

RESULTS

Thirty-nine per cent of patients developed IAH and 2% developed ACS. Abdominal distension, hemoperitoneum/pneumoperitoneum/intra-peritoneal fluid collection, obesity, intravenous fluid received > 2.3 l, abbreviated Sequential Organ Failure Assessment score > 4 points and lactate > 1.4 mmol/l were identified as independent predictors of IAH upon admission to ICU. The presence of three or more of these risk factors at admission identified patients that would develop IAH with a sensitivity of 75% and a specificity of 76%, the development of grades II, III and IV IAH with a sensitivity of 91% and a specificity of 62%. Patients that developed IAH required a significantly longer duration of mechanical ventilation and ICU care. Patients that developed grades II-IV IAH had a significantly higher rate of ICU mortality.

CONCLUSION

IAH is a common clinical entity in the intensive care setting that is associated with morbidity and mortality. A screening tool, based on data readily available within a patient's first 24 h in ICU, was developed and effectively identified patients that required intra-abdominal pressure monitoring.

Intra-abdominal hypertension and abdominal compartment syndrome: pathophysiological and non-operative management

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are conditions that commonly manifest in critically ill patients. They are associated with a multiplicity of pathophysiological disturbances. This study retrospectively reviewed literature relating to IAH and ACS published in the last two decades to consolidate an understanding of the epidemiology, etiology, pathophysiology, diagnosis and non-operative management of these conditions. Additionally, the authors of this study have recently conducted a large study on intra-abdominal pressures of consecutive catheterised patients admitted to the Intensive Care Unit (N.=403). A preliminary analysis of this study has also been included.

HIV-1 Vpr induces adipose dysfunction in vivo through reciprocal effects on PPAR/GR co-regulation

Viral infections, such as HIV, have been linked to obesity, but mechanistic evidence that they cause adipose dysfunction in vivo is lacking. We investigated a pathogenic role for the HIV-1 accessory protein viral protein R (Vpr), which can coactivate the glucocorticoid receptor (GR) and co-repress peroxisome proliferator-activated receptor γ (PPARγ) in vitro, in HIV-associated adipose dysfunction. Vpr circulated in the blood of most HIV-infected patients tested, including those on antiretroviral therapy (ART) with undetectable viral load. Vpr-mediated mechanisms were dissected in vivo using mouse models expressing the Vpr transgene in adipose tissues and liver (Vpr-Tg) or infused with synthetic Vpr. Both models demonstrated accelerated whole-body lipolysis, hyperglycemia and hypertriglyceridemia, and tissue-specific findings. Fat depots in these mice had diminished mass, macrophage infiltration, and blunted PPARγ target gene expression but increased GR target gene expression. In liver, we observed blunted PPARα target gene expression, steatosis with decreased adenosine monophosphate-activated protein kinase activity, and insulin resistance. Similar to human HIV-infected patients, Vpr circulated in the serum of Vpr-Tg mice. Vpr blocked differentiation in preadipocytes through cell cycle arrest, whereas in mature adipocytes, it increased lipolysis with reciprocally altered association of PPARγ and GR with their target promoters. These results delineate a distinct pathogenic sequence: Vpr, released from HIV-1 in tissue reservoirs after ART, can disrupt PPAR/GR co-regulation and cell cycle control to produce adipose dysfunction and hepatosteatosis. Confirmation of these mechanisms in HIV patients could lead to targeted treatment of the metabolic complications with Vpr inhibitors, GR antagonists, or PPARγ/PPARα agonists.

Masked and overt autoantibodies specific to the DPD epitope of 65-kDa glutamate decarboxylase (GAD65-DPD) are associated with preserved β-cell functional reserve in ketosis-prone diabetes

CONTEXT

Ketosis-prone diabetes (KPD), defined by presentation with diabetic ketoacidosis (DKA), comprises 4 subgroups based on the presence or absence of islet cell autoantibodies (A(-) or A(+)) and β-cell functional reserve (β(-) or β(+)). Among A(+) KPD, autoantibody epitope reactivity to 65-kDa glutamate decarboxylase (GAD65), defined by monoclonal GAD65Ab(DPD), was associated with greater β-cell functional reserve. In a majority of healthy individuals, GAD65Ab are present in the sera but are masked by anti-idiotypic antibodies; in contrast, overtly GAD65Ab-positive patients with autoimmune type 1 diabetes patients lack these anti-idiotypic antibodies.

OBJECTIVE

Our objective was to determine the presence of masked and overt GAD65Ab(DPD) in relation to β-cell function and genetic risk factors in KPD patients.

DESIGN

We investigated the associations of masked and overt GAD65Ab(DPD) with β-cell functional reserve, and their relationship with human leukocyte antigen (HLA) class II haplotypes linked to autoimmune diabetes susceptibility or resistance, in a large KPD cohort.

PATIENTS

Adult KPD patients (n = 384) were followed longitudinally in a research clinic.

MAIN OUTCOME MEASURES

β-Cell function, autoantibody status, GAD65Ab epitopes, and HLA class II haplotypes were evaluated.

RESULTS

Overall, KPD patients with β-cell functional reserve (β(+) subgroups) showed significantly higher frequency of masked GAD65Ab(DPD) than patients without β-cell functional reserve (β(-) subgroups): 112 of 144 (79%) compared with 59 of 100 (59%), respectively (P = .002). Masked or overt GAD65Ab(DPD) were also more frequent among autoantibody-positive patients with preserved β-cell functional reserve (A(+)β(+) KPD) than those lacking β-cell function (A(+)β(-) KPD): 77% compared with 55% (P = .01). The susceptibility HLA haplotypes DQA1*0301/DQB1*0302 and DQA1*0301/DQB1*0201 were associated with absence of overt or masked GAD65Ab(DPD) (odds Ratios 2.3 and 2.2, respectively).

CONCLUSIONS

Masked GAD65Ab(DPD) are strongly associated with preserved β-cell functional reserve among patients with KPD. Absence of GAD65Ab(DPD) reactivity is associated with 2 HLA class II susceptibility haplotypes for autoimmune type 1 diabetes.

Association of TCF7L2 variation with single islet autoantibody expression in children with type 1 diabetes

BACKGROUND

The transcription factor 7-like 2 (TCF7L2) gene has the strongest genetic association with type 2 diabetes. TCF7L2 also associates with latent autoimmune diabetes in adults, which often presents with a single islet autoantibody, but not with classical type 1 diabetes.

METHODS

We aimed to test if TCF7L2 is associated with single islet autoantibody expression in pediatric type 1 diabetes. We studied 71 prospectively recruited children who had newly diagnosed type 1 diabetes and evidence of islet autoimmunity, that is, expressed ≥1 islet autoantibody to insulin, glutamic acid decarboxylase 65, islet cell autoantigen 512, or zinc transporter 8. TCF7L2 rs7903146 alleles were identified. Data at diagnosis were cross-sectionally analyzed.

RESULTS

We found that 21.1% of the children with autoimmune type 1 diabetes expressed a single islet autoantibody. The distribution of TCF7L2 rs7903146 genotypes in children with a single autoantibody (n=15) was 40% CC, 26.7% CT and 33.3% TT, compared with children with ≥2 islet autoantibodies (50% CC, 42.9% CT and 7.1% TT, p=0.024). Furthermore, compared with children with ≥2 autoantibodies, single-autoantibody children had characteristics reflecting milder autoimmune destruction of β-cells. Restricting to lean children (body mass index<85th centile; n=36), 45.5% of those expressing a single autoantibody were rs7903146 TT homozygotes, compared with 0% of those with ≥2 autoantibodies (p<0.0001).

CONCLUSION

These results suggest that, in children with only mild islet autoimmunity, mechanisms associated with TCF7L2 genetic variation contribute to diabetogenesis, and this contribution is larger in the absence of obesity.

Islet-specific T-cell responses and proinflammatory monocytes define subtypes of autoantibody-negative ketosis-prone diabetes

OBJECTIVE

Ketosis-prone diabetes (KPD) is characterized by diabetic ketoacidosis (DKA) in patients lacking typical features of type 1 diabetes. A validated classification scheme for KPD includes two autoantibody-negative ("A-") phenotypic forms: "A-β-" (lean, early onset, lacking β-cell functional reserve) and "A-β+" (obese, late onset, with substantial β-cell functional reserve after the index episode of DKA). Recent longitudinal analysis of a large KPD cohort revealed that the A-β+ phenotype includes two distinct subtypes distinguished by the index DKA episode having a defined precipitant ("provoked," with progressive β-cell function loss over time) or no precipitant ("unprovoked," with sustained β-cell functional reserve). These three A- KPD subtypes are characterized by absence of humoral islet autoimmune markers, but a role for cellular islet autoimmunity is unknown.

RESEARCH DESIGN AND METHODS

Islet-specific T-cell responses and the percentage of proinflammatory (CD14+CD16+) blood monocytes were measured in A-β- (n = 7), provoked A-β+ (n = 15), and unprovoked A-β+ (n = 13) KPD patients. Genotyping was performed for type 1 diabetes-associated HLA class II alleles.

RESULTS

Provoked A-β+ and A-β- KPD patients manifested stronger islet-specific T-cell responses (P < 0.03) and higher percentages of proinflammatory CD14+CD16+ monocytes (P < 0.01) than unprovoked A-β+ KPD patients. A significant relationship between type 1 diabetes HLA class II protective alleles and negative T-cell responses was observed.

CONCLUSIONS

Provoked A-β+ KPD and A-β- KPD are associated with a high frequency of cellular islet autoimmunity and proinflammatory monocyte populations. In contrast, unprovoked A-β+ KPD lacks both humoral and cellular islet autoimmunity.

Impaired lipoprotein processing in HIV patients on antiretroviral therapy: aberrant high-density lipoprotein lipids, stability, and function

OBJECTIVE

HIV patients on antiretroviral therapy (HIV/ART) exhibit a unique atherogenic dyslipidemic profile with hypertriglyceridemia (HTG) and low plasma concentrations of high-density lipoprotein (HDL) cholesterol. In the Heart Positive Study of HIV/ART patients, a hypolipidemic therapy of fenofibrate, niacin, diet, and exercise reduced HTG and plasma non-HDL cholesterol concentrations and raised plasma HDL cholesterol and adiponectin concentrations. We tested the hypothesis that HIV/ART HDL have abnormal structures and properties and are dysfunctional.

APPROACH AND RESULTS

Hypolipidemic therapy reduced the TG contents of low-density lipoprotein and HDL. At baseline, HIV/ART low-density lipoproteins were more triglyceride (TG)-rich and HDL were more TG- and cholesteryl ester-rich than the corresponding lipoproteins from normolipidemic (NL) subjects. Very-low-density lipoproteins, low-density lipoprotein, and HDL were larger than the corresponding lipoproteins from NL subjects; HIV/ART HDL were less stable than NL HDL. HDL-[(3)H]cholesteryl ester uptake by Huh7 hepatocytes was used to assess HDL functionality. HIV/ART plasma were found to contain significantly less competitive inhibition activity for hepatocyte HDL-cholesteryl ester uptake than NL plasma were found to contain (P<0.001).

CONCLUSIONS

Compared with NL subjects, lipoproteins from HIV/ART patients are larger and more neutral lipid-rich, and their HDL are less stable and less receptor-competent. On the basis of this work and previous studies of lipase activity in HIV, we present a model in which plasma lipolytic activities or hepatic cholesteryl ester uptake are impaired in HIV/ART patients. These findings provide a rationale to determine whether the distinctive lipoprotein structure, properties, and function of HIV/ART HDL predict atherosclerosis as assessed by carotid artery intimal medial thickness.

Pathogenesis of A⁻β⁺ ketosis-prone diabetes

A⁻β⁺ ketosis-prone diabetes (KPD) is an emerging syndrome of obesity, unprovoked ketoacidosis, reversible β-cell dysfunction, and near-normoglycemic remission. We combined metabolomics with targeted kinetic measurements to investigate its pathophysiology. Fasting plasma fatty acids, acylcarnitines, and amino acids were quantified in 20 KPD patients compared with 19 nondiabetic control subjects. Unique signatures in KPD--higher glutamate but lower glutamine and citrulline concentrations, increased β-hydroxybutyryl-carnitine, decreased isovaleryl-carnitine (a leucine catabolite), and decreased tricarboxylic acid (TCA) cycle intermediates--generated hypotheses that were tested through stable isotope/mass spectrometry protocols in nine new-onset, stable KPD patients compared with seven nondiabetic control subjects. Free fatty acid flux and acetyl CoA flux and oxidation were similar, but KPD had slower acetyl CoA conversion to β-hydroxybutyrate; higher fasting β-hydroxybutyrate concentration; slower β-hydroxybutyrate oxidation; faster leucine oxidative decarboxylation; accelerated glutamine conversion to glutamate without increase in glutamate carbon oxidation; and slower citrulline flux, with diminished glutamine amide-nitrogen transfer to citrulline. The confluence of metabolomic and kinetic data indicate a distinctive pathogenic sequence: impaired ketone oxidation and fatty acid utilization for energy, leading to accelerated leucine catabolism and transamination of α-ketoglutarate to glutamate, with impaired TCA anaplerosis of glutamate carbon. They highlight a novel process of defective energy production and ketosis in A⁻β⁺ KPD.

Leptin replacement therapy does not improve the abnormal lipid kinetics of hypoleptinemic patients with HIV-associated lipodystrophy syndrome

Patients with HIV-associated dyslipidemic lipodystrophy (HADL) have characteristic lipid kinetic defects: accelerated lipolysis, blunted fat oxidation and increased hepatic fatty acid reesterification. HADL patients with lipoatrophy also have leptin deficiency. Small or non-randomized studies have suggested that leptin replacement improves glucose metabolism in HADL, with very limited data regarding its effects on the lipid kinetic abnormalities. We performed a randomized, double-blind, placebo-controlled, dose-escalating (0.02 mg/kg/d for two months; 0.04 mg/kg/d for a further two months) study of the effects of metreleptin on lipid kinetics in 17 adults with HADL, hypertriglyceridemia and hypoleptinemia. Rates of lipolysis, intra-adipocyte and intrahepatic reesterification and fatty acid oxidation were measured using infusions of (13)C(1)-palmitate and (2)H(5)-glycerol, and indirect calorimetry. Fasting lipid profiles and glucose and insulin responses to oral glucose challenge were also measured. Metreleptin treatment induced significant, dose-dependent increases in fasting plasma leptin levels. There was no significant change in total lipolysis, net lipolysis, adipocyte or hepatic re-esterification or fatty acid oxidation, or in fasting triglyceride or HDL-C concentrations, with metreleptin treatment. Metreleptin decreased fasting non-HDL-C levels (P<.01) and area-under-the-curve for glucose (P<.05). In hypoleptinemic HADL patients, treatment with metreleptin at 0.02 or 0.04 mg/kg/d does not improve abnormal fasting lipid kinetics, or triglyceride or HDL-C levels. Metreleptin does, however, improve glycemia and non-HDL-C in these patients. These results suggest a dissociation between leptin's effects on glucose metabolism compared to those on lipid kinetics in HADL.

Human monocytes accelerate proliferation and blunt differentiation of preadipocytes in association with suppression of C/EBPΑ mRNA

Obesity, type 2 diabetes, and HIV-associated lipodystrophy are associated with abnormalities in adipocyte growth and differentiation. In persons with these conditions, adipose depots contain increased numbers of macrophages, but the origins of these cells and their specific effects are uncertain. Peripheral blood mononuclear cells (PBMC)-derived monocytes, but not T cells, cocultured via transwells with primary subcutaneous preadipocytes, increased proliferation (approximately twofold) and reduced differentiation (~50%) of preadipocytes. Gene expression analyses in proliferating preadipocytes (i.e., prior to hormonal induction of terminal differentiation) revealed that monocytes down-regulated mRNA levels of CCAAT/enhancer binding protein, alpha (C/EBPα) and up-regulated mRNA levels of G0/G1 switch 2 (G0S2) message, genes important for the regulation of adipogenesis and the cell cycle. These data indicate that circulating peripheral blood monocytes can disrupt adipogenesis by interfering with a critical step in C/EBPα and G0S2 transcription required for preadipocytes to make the transition from proliferation to differentiation. Interactions between preadipocytes and monocytes also increased the inflammatory cytokines IL-6 and IL-8, as well as a novel chemotactic cytokine, CXCL1. Additionally, the levels of both IL-6 and CXCL1 were highest when preadipocytes and monocytes were cultured together, compared to each cell in culture alone. Such cross-talk amplifies the production of mediators of tissue inflammation.

A novel method of detection and classification of motor nerve late-wave activity

In motor nerve conduction studies, important diagnostic information is provided by the late-wave responses, comprised of F-waves, A-waves, and repeaters. Late-waves in addition to contamination from power line interference and baseline disturbance, are of low amplitude and random in nature. This makes computer-based analysis of late-wave activity very challenging, especially the computer-based F-wave onset latency assignment. Currently available algorithms assign latency independently on a trace-by-trace basis without considering the information present in an entire ensemble of traces. A novel algorithm that takes into account the ensemble information for segmenting and classifying regions of late-wave data is described in this paper, which in turn can be used to improve the performance of computer-based F-wave onset latency assignment.

Combination of niacin and fenofibrate with lifestyle changes improves dyslipidemia and hypoadiponectinemia in HIV patients on antiretroviral therapy: results of "heart positive," a randomized, controlled trial

CONTEXT

HIV patients on antiretroviral therapy (ART) have a unique dyslipidemia [elevated triglycerides and non-high-density lipoprotein-cholesterol (HDL-C), low HDL-C] with insulin resistance (characterized by hypoadiponectinemia).

OBJECTIVE

The aim was to test a targeted, comprehensive, additive approach to treating the dyslipidemia.

DESIGN AND SETTING

We conducted a randomized, double-blind, placebo-controlled, 24-wk trial of lifestyle modification, fenofibrate, and niacin in multiethnic HIV clinics at an academic center.

PARTICIPANTS

Hypertriglyceridemic adult patients were stratified on three combinations of ART classes. Subjects retained at the first measurement (2 wk) after entry were included in the analysis (n = 191).

INTERVENTIONS

Subjects were randomized into five treatment groups: usual care (group 1); low-saturated-fat diet and exercise (D/E; group 2); D/E + fenofibrate (group 3); D/E + niacin (group 4); or D/E + fenofibrate + niacin (group 5).

MAIN OUTCOME MEASURES

We measured changes in fasting triglycerides, HDL-C, and non-HDL-C (primary), and in insulin sensitivity, glycemia, adiponectin, C-reactive protein, energy expenditure, and body composition (secondary). Data were analyzed as a factorial set of treatment combinations using a mixed repeated measures model, last observation carried forward, and complete case approaches (groups 2-5), and as an unstructured set of treatments (groups 1-5).

RESULTS

Fenofibrate improved triglycerides (P = 0.002), total cholesterol (P = 0.02), and non-HDL-C (P = 0.003), whereas niacin improved HDL-C (P = 0.03), and both drugs decreased the total cholesterol-to-HDL-C ratio (P = 0.005-0.01). The combination of D/E, fenofibrate, and niacin provided maximal benefit, markedly reducing triglycerides (-52% compared to usual care; P = 0.003), increasing HDL-C (+12%; P < 0.001), and decreasing non-HDL-C (-18.5%; P = 0.003) and total cholesterol-to-HDL-C ratio (-24.5%; P < 0.001). Niacin doubled adiponectin levels.

CONCLUSIONS

A combination of fenofibrate and niacin with low-saturated-fat D/E is effective and safe in increasing HDL-C, decreasing non-HDL-C and hypertriglyceridemia, and ameliorating hypoadiponectinemia in patients with HIV/ART-associated dyslipidemia.

A-beta-subtype of ketosis-prone diabetes is not predominantly a monogenic diabetic syndrome

OBJECTIVE

Ketosis-prone diabetes (KPD) is an emerging syndrome that encompasses several distinct phenotypic subgroups that share a predisposition to diabetic ketoacidosis. We investigated whether the A-beta- subgroup of KPD, characterized by complete insulin dependence, absent beta-cell functional reserve, lack of islet cell autoantibodies, and strong family history of type 2 diabetes, represents a monogenic form of diabetes.

RESEARCH DESIGN AND METHODS

Over 8 years, 37 patients with an A-beta- phenotype were identified in our longitudinally followed cohort of KPD patients. Seven genes, including hepatocyte nuclear factor 4A (HNF4A), glucokinase (GCK), HNF1A, pancreas duodenal homeobox 1 (PDX1), HNF1B, neurogenic differentiation 1 (NEUROD1), and PAX4, were directly sequenced in all patients. Selected gene regions were also sequenced in healthy, unrelated ethnically matched control subjects, consisting of 84 African American, 96 Caucasian, and 95 Hispanic subjects.

RESULTS

The majority (70%) of the A-beta- KPD patients had no significant causal polymorphisms in either the proximal promoter or coding regions of the seven genes. The combination of six potentially significant low-frequency, heterozygous sequence variants in HNF-1 alpha (A174V or G574S), PDX1 (putative 5'-untranslated region CCAAT box, P33T, or P239Q), or PAX4 (R133W) were found in 27% (10/37) of patients, with one additional patient revealing two variants, PDX1 P33T and PAX4 R133W. The A174V variant has not been previously reported.

CONCLUSIONS

Despite its well-circumscribed, robust, and distinctive phenotype of severe, nonautoimmune-mediated beta-cell dysfunction, A-beta- KPD is most likely not a predominantly monogenic diabetic syndrome. Several A-beta- KPD patients have low-frequency variants in HNF1A, PDX1, or PAX4 genes, which may be of functional significance in their pathophysiology.

Regulation of cardiac specific nkx2.5 gene activity by small ubiquitin-like modifier

The cardiac specific homeobox gene nkx2.5, a member of the nk-2 class family, plays a central role in cardiogenesis and is a target of the small ubiquitin-like modifier (SUMO). Nkx2.5 was modified by SUMO on its 51st amino acid, a lysine residue conserved across species but absent in other nk-2 members. Conversion of this lysine to an arginine (K51R) substantially reduced Nkx2.5 DNA binding and also its transcriptional activity. Unexpectedly, mutant K51R was targeted by ubiquitin. E3 ligase PIAS proteins PIAS1, PIASx, and PIASy, but not PIAS3, enhanced SUMO-1 attachment to Nkx2.5 on the primary SUMO acceptor site. SUMO-2 linkage to Nkx2.5 was catalyzed only by PIASx and not by other PIAS proteins. SUMO conjugation stabilized the formation of Nkx2.5-containing complexes that led to robust transcriptional activation. Thus, SUMO modification serves as a positive regulator for Nkx2.5 transcriptional activity.

Detection and classification of motor nerve late-wave activity

The health of peripheral nerves is commonly assessed using nerve conduction studies, in which the nerve is stimulated electrically and the evoked responses are analyzed. In motor nerve studies, important diagnostic information is provided by the late-wave responses, comprised of F-waves, A-waves and repeaters. Computer-based analysis of late-wave activity is challenging due to the random nature and low amplitude of these signals. This paper describes an algorithm for segmenting portions of late-wave activity and classifying the type of evoked response. The algorithm may be used to improve the robustness of computer-based late-wave assessment.

Estimation of individual evoked potential components using iterative independent component analysis

Independent component analysis (ICA) has been successfully employed in the study of single-trial evoked potentials (EPs). In this paper, we present an iterative temporal ICA methodology that processes multielectrode single-trial EPs, one channel at a time, in contrast to most existing methodologies which are spatial and analyze EPs from all recording channels simultaneously. The proposed algorithm aims at enhancing individual components in an EP waveform in each single trial, and relies on a dynamic template to guide EP estimation. To quantify the performance of this method, we carried out extensive analyses with artificial EPs, using different models for EP generation, including the phase-resetting and the classical additive-signal models, and several signal-to-noise ratios and EP component latency jitters. Furthermore, to validate the technique, we employed actual recordings of the auditory N100 component obtained from normal subjects. Our results with artificial data show that the proposed procedure can provide significantly better estimates of the embedded EP signals compared to plain averaging, while with actual EP recordings, the procedure can consistently enhance individual components in single trials, in all subjects, which in turn results in enhanced average EPs. This procedure is well suited for fast analysis of very large multielectrode recordings in parallel architectures, as individual channels can be processed simultaneously on different processors. We conclude that this method can be used to study the spatiotemporal evolution of specific EP components and may have a significant impact as a clinical tool in the analysis of single-trial EPs.

Comparison between ICA and wavelet-based denoising of single-trial evoked potentials

Analysis of evoked potentials (EPs) on a single-trial basis allows the study of the dynamical characteristics of brain activity. However, single-trial responses are buried into the more prominent ongoing electroencephalographic (EEG) activity, and thus advanced procedures are needed to obtain the activity only of the cortical generators that are activated by the experimental task under study. We compare the effectiveness of two methods at removing extraneous activity from single-trial EPs, namely, a recently-proposed iterative procedure based on independent component analysis (ICA) and wavelet denoising, using simulated data and actual EP recordings from normal subjects, more specifically the auditory N100-P200 complex.

Association of amino-terminal-specific antiglutamate decarboxylase (GAD65) autoantibodies with beta-cell functional reserve and a milder clinical phenotype in patients with GAD65 antibodies and ketosis-prone diabetes mellitus

CONTEXT

We previously characterized patients presenting with diabetic ketoacidosis prospectively into four subgroups of ketosis-prone diabetes mellitus (KPDM), based on the presence or absence of beta-cell autoimmunity (A+ or A-) and beta-cell functional reserve (B+ or B-). The A+B- KPDM subgroup comprises patients with classic, autoimmune type 1 diabetes, whereas the A+B+ KPDM subgroup has only partial beta-cell loss and a distinct clinical phenotype.

OBJECTIVE

We hypothesized that epitope specificity of autoantibodies directed against the 65-kDa isoform of glutamate decarboxylase (GAD65) reflects differences in beta-cell destruction.

DESIGN

Sera of sequential GAD65Ab-positive KPDM patients admitted for diabetic ketoacidosis (n = 36) were analyzed for their epitope recognition using five GAD65-specific recombinant Fab and their ability to inhibit GAD65 enzymatic activity. All patients were followed longitudinally to assess beta-cell functional reserve and insulin dependence.

RESULTS

Binding to an amino-terminal epitope defined by monoclonal antibody DPD correlated positively with fasting serum C-peptide levels at baseline (P = 0.0008) and after 1 yr (P = 0.007). Binding to the DPD-defined epitope also correlated positively with area under the curve for C-peptide after glucagon stimulation (P = 0.007) and with homeostasis model assessment percent B at 1 yr (P = 0.03). Binding to the DPD-defined epitope was significantly stronger in A+B+ than in A+B- patients (P = 0.001). Sera of 16 patients (44%) significantly inhibited GAD65 enzymatic activity, but this did not correlate with beta-cell function.

CONCLUSION

DPD-defined epitope specificity is correlated directly with preserved beta-cell functional reserve in GAD65Ab-positive patients and is associated with the milder clinical phenotype of A+B+ KPDM.

Effects of transgenic expression of HIV-1 Vpr on lipid and energy metabolism in mice

HIV infection is associated with abnormal lipid metabolism, body fat redistribution, and altered energy expenditure. The pathogenesis of these complex abnormalities is unclear. Viral protein R (Vpr), an HIV-1 accessory protein, can regulate gene transcription mediated by the glucocorticoid receptor and peroxisome proliferator-activated receptor-gamma and affect mitochondrial function in vitro. To test the hypothesis that expression of Vpr in liver and adipocytes can alter lipid metabolism in vivo, we engineered mice to express Vpr under control of the phosphoenolpyruvate carboxykinase promoter in a tissue-specific and inducible manner and investigated the effects of dietary fat, indinavir, and dexamethasone on energy metabolism and body composition. The transgenic mice expressed Vpr mRNA in white and brown adipose tissues and liver and immunoaffinity capillary electrophoresis revealed that they had free Vpr protein in the plasma. Compared with wild-type (WT) animals, Vpr mice had lower plasma triglyceride levels after 6 wk (P < 0.05) but not after 10 wk of a high-fat diet and lower plasma cholesterol levels after 10 wk of high-fat diet (P < 0.05). Treatment with dexamethasone obviated group differences, whereas indinavir had no significant independent effect on lipids. In the fasted state, Vpr mice had a higher respiratory quotient than WT mice (P < 0.05). These data provide the first in vivo evidence that HIV-1 Vpr expressed at low levels in adipose tissues and liver can 1) circulate in the blood, 2) regulate lipid and fatty acid metabolism, and 3) alter fuel selection for oxidation in the fasted state.

Rise of plasma ghrelin with weight loss is not sustained during weight maintenance

OBJECTIVE

Ghrelin is postulated to be an orexigenic signal that promotes weight regain after weight loss (WL). However, it is not known whether this putative effect of ghrelin is sustained after weight stabilization. The objective of this study was to investigate the relationship of plasma ghrelin concentrations to active WL and weight maintenance in obese subjects.

RESEARCH METHODS AND PROCEDURES

This study was a randomized clinical trial, with a 12-month follow-up period. Obese Mexican-American women matched for age and BMI were randomized to a 12-month WL program (n = 25) or no intervention (controls, n = 23). Interventions included diet, exercise, and orlistat. Body weight and fasting ghrelin, leptin, insulin, and glucose concentrations were measured at baseline and 6 and 12 months.

RESULTS

The WL group lost 8.5% of body weight after 6 months and maintained the new weight for the next 6 months. Ghrelin concentrations increased significantly at 6 months but returned to baseline at 12 months. Baseline ghrelin concentrations were directly related to the degree of WL achieved after 12 months. Controls experienced no change in BMI or ghrelin levels. There were no associations between plasma ghrelin and leptin or insulin concentrations.

DISCUSSION

Consistent with previous results, ghrelin rises in response to WL, perhaps as a counterregulatory mechanism. However, the present results indicate that ghrelin concentrations return to baseline with sustained weight maintenance, suggesting that its effects are unlikely to regulate long-term energy balance. Baseline ghrelin concentrations are related to the degree of WL that can be achieved by active weight reduction.

Serum response factor MADS box serine-162 phosphorylation switches proliferation and myogenic gene programs

Phosphorylation of a cluster of amino acids in the serum response factor (SRF) "MADS box" alphaI coil DNA binding domain regulated the transcription of genes associated with proliferation or terminal muscle differentiation. Mimicking phosphorylation of serine-162, a target of protein kinase C-alpha, with an aspartic acid substitution (SRF-S162D) completely inhibited SRF-DNA binding and blocked alpha-actin gene transcription even in the presence of potent myogenic cofactors, while preserving c-fos promoter activity because of stabilization of the ternary complex via Elk-1. Introduction of SRF-S162D into SRF null ES cells permitted transcription of the c-fos gene but was unable to rescue expression of myogenic contractile genes. Transition of proliferating C2C12 myoblasts to postfusion myocytes after serum withdrawal was associated with a progressive decline in SRF-S162 phosphorylation and an increase in alpha-actin gene expression. Hence, the phosphorylation status of serine-162 in the alphaI coil may constitute a novel switch that directs target gene expression into proliferation or differentiation programs.

Severely dysregulated disposal of postprandial triacylglycerols exacerbates hypertriacylglycerolemia in HIV lipodystrophy syndrome

BACKGROUND

The pathogenesis of hypertriacylglycerolemia, a characteristic feature of HIV lipodystrophy syndrome (HLS), is incompletely understood. One mechanism is accelerated lipolysis in the fasted state, but the severity of the hypertriacylglycerolemia suggests that additional underlying abnormalities may exist in the disposal of dietary fat.

OBJECTIVE

Our objective was to investigate abnormalities in dietary fat disposal in the pathogenesis of hypertriacylglycerolemia in HLS.

DESIGN

We studied 6 nondiabetic men with HLS and 6 men without HIV matched for age and body mass index as control subjects for 8 h after consumption of an isocaloric meal containing 2 g labeled [(13)C(3)]tripalmitin. Chylomicron-triacylglycerol disposal was estimated from labeled [(13)C(1)]palmitate in the plasma chylomicron fraction, and [(13)C(1)]palmitate oxidation was estimated from the (13)CO(2) enrichment in the breath and CO(2) production, over 8 h after the meal.

RESULTS

HLS patients had significantly elevated concentrations of fasting plasma triacylglycerols in both chylomicron (x + SE: 100.3 +/- 49.5 compared with 29.2 +/- 2.2 mg/dL; P < 0.01) and VLDL (82.4 +/- 39.0 compared with 10.8 +/- 2.8 mg/dL; P < 0.01) fractions. Chylomicron-triacylglycerol-derived [(13)C(1)]palmitate disposal was markedly lower in the HLS patients (3.09 +/- 0.41 compared with 6.42 +/- 0.18 mmol [(13)C(1)]palmitate/8 h; P < 0.001) in the 8-h postmeal period. Further, HLS patients had lowered storage of chylomicron-triacylglycerols (0.74 +/- 0.38 compared with 5.05 +/- 0.16 mmol; P < 0.0001) and elevated plasma [(13)C(1)]palmitate concentrations (2.01 +/- 0.27 compared with 1.18 +/- 0.16 mmol; P < 0.05) 8 h after the meal.

CONCLUSIONS

Patients with HLS have key defects that markedly impair postprandial disposal and storage of chylomicron-triacylglycerols. These defects contribute significantly to hypertriacylglycerolemia in HLS.

Ketosis-prone diabetes: dissection of a heterogeneous syndrome using an immunogenetic and beta-cell functional classification, prospective analysis, and clinical outcomes

Ketosis-prone diabetes is heterogeneous. Its causes could include novel beta-cell functional defects. To characterize such defects, 103 patients with diabetic ketoacidosis were evaluated for beta-cell autoimmunity and human leukocyte antigen (HLA) class II alleles, with longitudinal measurements of beta-cell function and biochemical and clinical parameters. They were classified into four A beta groups, based on the presence of glutamic acid decarboxylase (GAD)65, GAD67, or IA-2 autoantibodies (A+ or A-) and beta-cell functional reserve (beta+ or beta-). The group distribution was: 18 A+beta-, 23 A-beta-, 11 A+beta+, and 51 A-beta+. Collectively, the two beta- groups differed from the two beta+ groups in earlier onset and longer duration of diabetes, lower body mass index, less glycemic improvement, and persistent insulin requirement. HLA class II genotyping showed that the A-beta- group differed from the A+beta- group in having lower frequencies of two alleles strongly associated with autoimmune type 1 diabetes susceptibility: DQA*03 and DQB1*02. Similarly, the A-beta+ group differed from the A+beta+ group in having a lower frequency of DQB1*02. Ketosis-prone diabetes comprises at least four etiologically distinct syndromes separable by autoantibody status, HLA genotype, and beta-cell functional reserve. Novel, nonautoimmune causes of beta-cell dysfunction are likely to underlie the A-beta+ and A-beta- syndromes.

Novel phosphorylation target in the serum response factor MADS box regulates alpha-actin transcription

Serum response factor (SRF) is a phosphoprotein that regulates skeletal and cardiac alpha-actin gene transcription. Myotonic dystrophy protein kinase (DMPK), a muscle- and neuron-restricted kinase, enhanced SRF-mediated promoter activity of the skeletal and cardiac alpha-actin genes in C2C12 myoblasts as well as in nonmyogenic cells. DMPK phosphorylated SRF in vitro in the alphaI coil of the DNA-binding domain in the MADS box, a highly conserved region required for DNA binding, dimerization, and co-activator interaction in COS and CV1 cells. Threonine 159 in the MADS box alphaI coil was a specific phosphorylation target in vitro as well as in vivo of both DMPK and protein kinase C-alpha. Substitution of threonine 159 with the nonphosphorylatable residue alanine markedly diminished activation of the cardiac alpha-actin promoter in the presence of kinase, while its substitution with aspartic acid, to introduce a negative charge and mimic phosphorylation, restored activation completely. Phosphorylation of the MADS box may constitute a novel mechanism for regulation of SRF-dependent actin gene transcription.

Improved outcomes in indigent patients with ketosis-prone diabetes: effect of a dedicated diabetes treatment unit

OBJECTIVE

To investigate whether a specialized intervention program could improve diabetes-related health outcomes in indigent patients with type 1 diabetes who were prone to occurrence of diabetic ketoacidosis (DKA).

METHODS

Patients with type 1 diabetes mellitus admitted because of DKA during a 24-month period were invited to receive outpatient care in a diabetes treatment unit (DTU). We compared DKA-related readmission rates, change in hemoglobin A1c (HbA1c) values, and diabetes-related medical costs in patients who participated in the DTU program (+DTU) and in those who did not (-DTU).

RESULTS

During the study period, 115 patients underwent assessment. Of this overall group, 57 patients (49.6%) consented to participate in the DTU program, and 58 (50.4%) did not. After the follow-up period (median duration, 657 days), the following significant improvements were observed in the +DTU group (in comparison with the -DTU group): lower frequency of readmission for DKA (16% versus 43%; P = 0.001), lower number of readmissions for DKA per patient (0.22 +/- 0.6 versus 1.17 +/- 2.2 [mean +/- standard deviation]; P = 0.003), lower HbA1c level (10.4 +/- 2.3% versus 13.5 +/- 2.3%; P<0.0001), and lower cost of diabetes-related medical care (3,427.20 US dollars +/- 6,275.60 versus 10,119.10 US dollars +/- 19,688.10; P = 0.01). Multivariate analysis revealed that participation in the DTU program was the only factor associated with a significantly decreased risk of DKA-related readmission.

CONCLUSION

Low-cost intervention by a dedicated outpatient DTU resulted in significant decreases in DKA-associated readmissions, in HbA1c values, and in costs of diabetes care in a multiethnic, indigent, ketosis-prone patient population.

Cysteine-rich LIM-only proteins CRP1 and CRP2 are potent smooth muscle differentiation cofactors

Cysteine-rich LIM-only proteins, CRP1 and CRP2, expressed during cardiovascular development act as bridging molecules that associate with serum response factor and GATA proteins. SRF-CRP-GATA complexes strongly activated smooth muscle gene targets. CRP2 was found in the nucleus during early stages of coronary smooth muscle differentiation from proepicardial cells. A dominant-negative CRP2 mutant blocked proepicardial cells from differentiating into smooth muscle cells. Together with SRF and GATA proteins, CRP1 and CRP2 converted pluripotent 10T1/2 fibroblasts into smooth muscle cells, while muscle LIM protein CRP3 inhibited the conversion. Thus, LIM-only proteins of the CRP family play important roles in organizing multiprotein complexes, both in the cytoplasm, where they participate in cytoskeletal remodeling, and in the nucleus, where they strongly facilitate smooth muscle differentiation.

Developmental expression of serum response factor in the rat central nervous system

Serum response factor (SRF), a transcription factor known to be essential for early embryonic development as well as post-natal regulation of both cellular proliferation and myogenic differentiation, is expressed broadly in neurons within the adult mammalian central nervous system (CNS). The function of SRF within the developing CNS is not well established, but it is likely to play an important role in neuraxial development and neuronal function, since many of its known target genes (e.g., c-fos) and transcriptional partners (e.g., Elk-1) are also highly expressed in neurons. Immunohistochemical survey of the post-natal developing rat brain revealed a progressive increase in SRF immunoreactivity in neurons of the cerebral and cerebellar cortices, and in selective subcortical regions from birth (P0) through post-natal day 28 (P28). SRF immunoreactivity stabilized from P28 into adulthood. A few loci, such as the nucleus of cranial nerve VII, showed the reverse expression pattern (strong immunoreactivity at P0-P7, declining by P28). The developmental expression pattern of SRF overlaps significantly with that of myotonic dystrophy protein kinase, a potential upstream regulator, and of the LIM-only genes Lmo1, Lmo2 and Lmo3, whose products belong to a family of proteins known to be strong positive regulators of SRF's transcriptional activity. These data suggest that SRF has a significant function in the early post-natal development of the CNS.