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Abstract Background Familial partial lipodystrophy (Dunnigan) type 3 (FPLD3, Mendelian Inheritance in Man [MIM] 604367) results from heterozygous mutations in PPARG encoding peroxisomal proliferator-activated receptor-γ. Both dominant-negative and haploinsufficiency mechanisms have been suggested for this condition. Methods We present a Canadian FPLD3 kindred with an affected mother who had loss of fat on arms and legs, but no increase in facial, neck, suprascapular or abdominal fat. She had profound insulin resistance, diabetes, severe hypertriglyceridemia and relapsing pancreatitis, while her pre-pubescent daughter had normal fat distribution but elevated plasma triglycerides and C-peptide and depressed high-density lipoprotein cholesterol. Results The mother and daughter were each heterozygous for PPARG nonsense mutation Y355X, whose protein product in vitro was transcriptionally inactive with no dominant-negative activity against the wild-type receptor. In addition the mutant protein appeared to be markedly unstable. Conclusion Taken together with previous studies of human PPARG mutations, these findings suggest that PPAR-γ deficiency due either to haploinsufficiency or to substantial activity loss due to dominant negative interference of the normal allele product's function can each contribute to the FPLD3 phenotype.

COP9 constitutive photomorphogenic homolog subunit 5 (COPS5), also known as Jab1 or CSN5, has been implicated in a wide variety of cellular and developmental processes. By analyzing male germ cell-specific COPS5-deficient mice, we have demonstrated previously that COPS5 is essential to maintain male germ survival and acrosome biogenesis. To further determine the role of Cops5 in peritubular myoid cells, a smooth muscle lineage surrounding seminiferous tubules, we herein derived mice conditionally deficient for the Cops5 gene in smooth muscle cells using transgenic Myh11-Cre mice. Although these conditional Cops5-deficient mice were born at the expected Mendelian ratio and appeared to be normal within the first week after birth, the homozygous mice started to show growth retardation after 1 week. These mice also exhibited a variety of developmental and reproductive disorders, including failure of development of reproductive organs in both males and females, spermatogenesis defects, and impaired skeletal development and immune functions. Furthermore, conditional Cops5-deficient mice revealed dramatic impairment of the endocrine system associated with testicular functions, including a marked reduction in serum levels of gonadotropins (follicle-stimulating hormone, luteinizing hormone), testosterone, insulin-like growth factor 1, and glucose, but not vasopressin. All homozygous mice died before age 67 days in the study. Collectively, our results provide novel evidence that Cops5 in smooth muscle lineage plays an essential role in postnatal development and reproductive functions., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In both humans and rodent models, circulating glycine levels are significantly reduced in obesity, glucose intolerance, type II diabetes, and non-alcoholic fatty liver disease. The glycine cleavage system and its rate-limiting enzyme, glycine decarboxylase (GLDC), is a major determinant of plasma glycine levels. The goals of this study were to determine if the increased expression of GLDC contributes to the reduced plasma glycine levels seen in disease states, to characterize the hormonal regulation of GLDC gene expression, and to determine if altered GLDC expression has physiological effects that might affect the development of diabetes. The findings presented here show that hepatic GLDC gene expression is elevated in mouse models of obesity and diabetes, as well as by fasting. We demonstrated that GLDC gene expression is strongly regulated by the metabolic hormones glucagon and insulin, and we identified the signaling pathways involved in this regulation. Finally, we found that GLDC expression is linked to glutathione levels, with increased expression associated with elevated levels of glutathione and reduced expression associated with a suppression of glutathione and increased cellular ROS levels. These findings suggest that the hormonal regulation of GLDC contributes not only to the changes in circulating glycine levels seen in metabolic disease, but also affects glutathione production, possibly as a defense against metabolic disease-associated oxidative stress., (© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Adiponectin (ADN) is an abundant protein in serum, secreted by adipocytes, that acts as a signal for fat metabolism. It is marked by a complex molecular structure that results from processes within the secretory pathway, producing a canonical set of multimers. ADN may also be secreted from cardiomyocytes, where a unique sarcomeric endoplasmic/sarcoplasmic reticulum (ER/SR) substructure has been characterized primarily for its Ca handling. We expressed ADN in cultured primary adult cardiomyocytes and nonmuscle (COS) cells. After 48 h of ADN expression by adenovirus treatment, roughly half of synthesized ADN was secreted from cardiomyocytes, and half was still in-transit within inner membrane compartments, similar to COS cells. Cardiomyocytes and COS cells both produced ADN in the three canonical forms: trimers, hexamers, and 18-mers. Higher rates of secretion occurred for higher-molecular weight multimers, especially 18-mers. The highest levels of ADN protein, whether in transit or secreted, were present as trimers and hexamers. In nonmuscle cell lines, ADN trafficked through ER and Golgi compartments as expected. In contrast, ADN in primary adult cardiomyocytes populated ER/SR tubules along the edges of sarcomeres that emanated from nuclear surfaces. Prominent co-localization of ADN occurred with calsequestrin, a marker of junctional SR, the Ca 2+ -release compartment of the cell. The early steps in ADN trafficking re-trace those recently described for newly made junctional SR proteins, involving a nuclear envelope (NE) translocation into SR tubules that are oriented along sarcolemmal transverse (T)-tubules (NEST pathway).

Although the increased incidence of type 2 diabetes since the 1950s is thought to be primarily due to coincident alterations in lifestyle factors, another potential contributing factor in industrialized countries is exposure of the population to environmental pollutants and industrial chemicals. Exposure levels of many environmental toxicants have risen in the same time-frame as the disease incidence. Of particular interest in this regard is the metal lead. Although overall lead exposure levels have diminished in recent decades, there is an under-recognized but persistent occurrence of lead exposure in poor underserved urban populations. Although the neural developmental pathologies induced by lead exposures have been well documented, very little is known about the effect of lead exposure on the incidence of chronic metabolic diseases such as type 2 diabetes. Although our understanding of the metabolic health effects of lead exposure is incomplete, there are studies in model systems and a small amount of epidemiological data that together suggest a deleterious effect of environmental lead exposure on metabolic health. This article reviews the human, animal and in vitro studies that have examined the effects of lead exposure on the development of diabetes and related metabolic conditions.

Background: Pb (lead) exposure occurs at elevated frequency in urban inner city populations that also have high rates of obesity and diabetes., Objectives: To determine if Pb can promote the development of diabetes in a setting of obesity, we examined the effect of Pb exposure on glucose metabolism in a rodent model of obesity., Methods: Adult female ZDF rats were exposed to Pb in drinking water for 24 weeks. Fasting blood glucose, insulin, and glucose tolerance were measured at regular intervals. Expression of hepatic gluconeogenic genes was measured in exposed and control animals and in cultured hepatoma cells treated with Pb., Results: Pb exposure induced fasting hyperglycemia after 8 weeks and glucose intolerance after 12 weeks of exposure. In addition, Pb-exposed animals showed elevated hepatic triglyceride levels and increased expression of the gluconeogenic genes PEPCK and glucose-6-phosphatase. In cultured rat hepatoma cells treatment with Pb stimulated PEPCK and glucose-6-phosphatase gene expression, suggesting a possible direct effect of Pb on hepatic gluconeogenic gene expression., Conclusions: In the setting of obesity, Pb exposure is prodiabetic, causing fasting hyperglycemia and glucose intolerance in rats. A contributing factor to the metabolic effects of Pb may be the direct stimulation of hepatic gluconeogenic gene expression., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

The focus of this review is the lipodystrophy syndrome caused by mutation in the PPARγ nuclear receptor - partial familial lipodystrophy FPLD3. To provide a broader context for how these mutations act to generate the clinical features of partial lipodystrophy we will review the basic biology of PPARγ and also survey the set PPARγ genetic variants that do not cause lipodystrophy, but are nonetheless associated with clinically related syndromes, specifically type 2 diabetes.

Congenital generalized lipodystrophy (CGL), secondary to AGPAT2 mutation is characterized by the absence of adipocytes and development of severe insulin resistance. In the current study, we investigated the adipogenic defect associated with AGPAT2 mutations. Adipogenesis was studied in muscle-derived multipotent cells (MDMCs) isolated from vastus lateralis biopsies obtained from controls and subjects harboring AGPAT2 mutations and in 3T3-L1 preadipocytes after knockdown or overexpression of AGPAT2. We demonstrate an adipogenic defect using MDMCs from control and CGL human subjects with mutated AGPAT2. This defect was rescued in CGL MDMCs with a retrovirus expressing AGPAT2. Both CGL-derived MDMCs and 3T3-L1 cells with knockdown of AGPAT2 demonstrated an increase in cell death after induction of adipogenesis. Lack of AGPAT2 activity reduces Akt activation, and overexpression of constitutively active Akt can partially restore lipogenesis. AGPAT2 modulated the levels of phosphatidic acid, lysophosphatidic acid, phosphatidylinositol species, as well as the peroxisome proliferator-activated receptor γ (PPARγ) inhibitor cyclic phosphatidic acid. The PPARγ agonist pioglitazone partially rescued the adipogenic defect in CGL cells. We conclude that AGPAT2 regulates adipogenesis through the modulation of the lipome, altering normal activation of phosphatidylinositol 3-kinase (PI3K)/Akt and PPARγ pathways in the early stages of adipogenesis.

Familial partial lipodystrophy (FPLD) is characterized by abnormal fat distribution and a metabolic syndrome with hypertriglyceridemia. We identified a family with a severe form of FPLD3 with never-reported clinical features and a novel mutation affecting the DNA binding domain of PPARγ (E157D). Apart from the lipodystrophy and severe metabolic syndrome, individuals presented musculoskeletal and hematological issues. E157D heterozygotes had a muscular habitus yet displayed muscle weakness and myopathy. Also, E157D heterozygotes presented multiple cytopenias and a susceptibility to autoimmune disease. In vitro studies showed that the E157D mutation does not decrease the receptor's affinity to classical PPAR response elements or its responsiveness to a PPARγ agonist, yet it severely reduces its target gene transcription. Microarray experiments demonstrated a decreased activation of a wide array of genes, including genes involved in the PPAR response, the immune response, hematopoiesis, and metabolism in muscle. In addition, a subset of genes with cryptic PPAR response elements was activated. In summary, we describe a large family with a novel PPARγ mutation, which extends the clinical phenotype of FPLD3 to include muscular, immune, and hematological features. Together, our results support the role of PPARγ in controlling homeostasis of multiple systems beyond lipid metabolism.

β-Adrenergic receptors (β-ARs) promote brown adipose tissue (BAT) thermogenesis by mobilizing fatty acids and inducing the expression of oxidative genes. β-AR activation increases the expression of oxidative genes by elevating cAMP, but whether lipolytic products can modulate gene expression is not known. This study examined the role that adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) plays in the induction of gene expression. Activation of brown adipocytes by β-AR agonism or 8-bromo-cyclic AMP increased the expression of PGC1α, PDK4, PPARα, uncoupling protein 1 (UCP1), and neuron-derived orphan receptor-1 (NOR-1), and concurrent inhibition of HSL reduced the induction of PGC1α, PDK4, PPARα, and UCP1 but not NOR-1. Similar results were observed in the BAT of mice following pharmacological or genetic inhibition of HSL and in brown adipocytes with stable knockdown of ATGL. Conversely, treatments that increase endogenous fatty acids elevated the expression of oxidative genes. Pharmacological antagonism and siRNA knockdown indicate that PPARα and PPARδ modulate the induction of oxidative genes by β-AR agonism. Using a live cell fluorescent reporter assay of PPAR activation, we demonstrated that ligands for PPARα and -δ, but not PPARγ, were rapidly generated at the lipid droplet surface and could transcriptionally activate PPARα and -δ. Knockdown of ATGL reduced cAMP-mediated induction of genes involved in fatty acid oxidation and oxidative phosphorylation. Consequently, ATGL knockdown reduced maximal oxidation of fatty acids, but not pyruvate, in response to cAMP stimulation. Overall, the results indicate that lipolytic products can activate PPARα and PPARδ in brown adipocytes, thereby expanding the oxidative capacity to match enhanced fatty acid supply.

The recent advances in the understanding of adiponectin and other adipokines have highlighted the role of adipose tissue as an active endocrine organ. One of the central regulators of adipocyte biology is peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that induces the adipogenic gene expression program during development, promotes adipose remodeling, and regulates the functions of adipocytes in lipid storage, adipokine secretion, and energy homeostasis. Activation of PPARγ results in increased insulin sensitivity in skeletal muscle and liver and improves the secretory profile of adipose tissue, favoring release of insulin-sensitizing adipokines, such as adiponectin, and reducing inflammatory cytokines. Increased adiponectin production is likely a significant mediator of the systemic effects of PPARγ activation. This chapter will review the interplay between PPARγ and adiponectin in regulating metabolism, presenting evidence that PPARγ regulates adiponectin gene expression, processing, and secretion and that the two proteins have overlapping effects on downstream metabolic pathways., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Accumulating evidence highlights intriguing interplays between circadian and metabolic pathways. We show that PER2 directly and specifically represses PPARγ, a nuclear receptor critical in adipogenesis, insulin sensitivity, and inflammatory response. PER2-deficient mice display altered lipid metabolism with drastic reduction of total triacylglycerol and nonesterified fatty acids. PER2 exerts its inhibitory function by blocking PPARγ recruitment to target promoters and thereby transcriptional activation. Whole-genome microarray profiling demonstrates that PER2 dictates the specificity of PPARγ transcriptional activity. Indeed, lack of PER2 results in enhanced adipocyte differentiation of cultured fibroblasts. PER2 targets S112 in PPARγ, a residue whose mutation has been associated with altered lipid metabolism. Lipidomic profiling demonstrates that PER2 is necessary for normal lipid metabolism in white adipocyte tissue. Our findings support a scenario in which PER2 controls the proadipogenic activity of PPARγ by operating as its natural modulator, thereby revealing potential avenues of pharmacological and therapeutic intervention., (Copyright © 2010 Elsevier Inc. All rights reserved.)

In experimental animal and cell culture models, activation of peroxisome proliferator-activated receptor (PPAR) gamma in heart has been shown to have beneficial effects on cardiac function and cardiomyocyte physiology. The goal of this study was to identify the signaling pathway by which PPARgamma activation protects cardiomyocytes from the deleterious effects of hypertrophic stimuli. In primary cardiomyocyte cultures, we found that genetic or pharmacological activation of PPARgamma protected cells from cardiac hypertrophy induced by alpha-adrenergic stimulation. Examination of gene expression in these cells revealed a surprising increase in the expression of adiponectin in cardiomyocytes and secretion of the high-molecular-weight form of the hormone into media. Using RNAi to block PPARgamma-induced adiponectin production or adiponectin receptor gene expression, we found that the PPARgamma-mediated anti-hypertrophic effect required cardiomyocyte-produced adiponectin, as well as an intact adiponectin signaling pathway. Furthermore, mice expressing constitutive-active PPARgamma and cardiomyocyte specific adiponectin expression were protected from high-fat diet-induced cardiac hypertrophy and remodeling. These findings demonstrate that functional adiponectin hormone can be produced from the heart and raise the possibility that beneficial effects of PPARgamma activation in heart could be due in part to local production of adiponectin that acts on cardiomyocytes in an autocrine manner.

Age-related thymic involution is characterized by reduction in T cell production together with ectopic adipocyte development within the hematopoietic and thymic niches. Peroxisome proliferator-activated receptor gamma (PPARgamma) is required for adipocyte development, glucose homeostasis and is a target for several insulin-sensitizing drugs. Our prior studies showed that age-related elevation of PPARgamma expression in thymic stromal cells is associated with thymic involution. Here, using clinically relevant pharmacological and genetic manipulations in mouse models, we provide evidence that activation of PPARgamma leads to reduction in thymopoiesis. Treatment of aged mice with antihyperglycemic PPARgamma-ligand class of thiazolidinedione drug, rosiglitazone caused robust thymic expression of classical pro-adipogenic transcripts. Rosiglitazone reduced thymic cellularity, lowered the naïve T cell number and T cell receptor excision circles (TRECs) indicative of compromised thymopoiesis. To directly investigate whether PPARgamma activation induces thymic involution, we created transgenic mice with constitutive-active PPARgamma (CA-PPARg) fusion protein in cells of adipogenic lineage. Importantly, CA-PPARgamma transgene was expressed in thymus and in fibroblast-specific protein-1/S100A4 (FSP1(+)) cells, a marker of secondary mesenchymal cells. The CAPPARgamma fusion protein mimicked the liganded PPARgamma receptor and the transgenic mice displayed increased ectopic thymic adipogenesis and reduced thymopoiesis. Furthermore, the reduction in thymopoiesis in CA-PPARgamma mice was associated with higher bone marrow adiposity and lower hematopoietic stem cell progenitor pool. Consistent with lower thymic output, CAPPARgamma transgenic mice had restricted T cell receptor repertoire diversity. Collectively, our data suggest that activation of PPARgamma accelerates thymic aging and thymus-specific PPARgamma antagonist may forestall age-related decline in T cell diversity.

The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma plays a key role in regulating whole body glucose homeostasis and insulin sensitivity. Although it is expressed most highly in adipose, it is also present at lower levels in many tissues, including skeletal muscle. The role muscle PPARgamma plays in metabolic regulation and in mediating the antidiabetic effects of the thiazolidinediones is not understood. The goal of this work was to examine the molecular and physiological effects of PPARgamma activation in muscle cells. We found that pharmacological activation of PPARgamma in primary cultured myocytes, and genetic activation of muscle PPARgamma in muscle tissue of transgenic mice, induced the production of adiponectin directly from muscle cells. This muscle-produced adiponectin was functional and capable of stimulating adiponectin signaling in myocytes. In addition, elevated skeletal muscle PPARgamma activity in transgenic mice provided a significant protection from high-fat diet-induced insulin resistance and associated changes in muscle phenotype, including reduced myocyte lipid content and an increase in the proportion of oxidative muscle fiber types. Our findings demonstrate that PPARgamma activation in skeletal muscle can have a significant protective effect on whole body glucose homeostasis and insulin resistance and that myocytes can produce and secrete functional adiponectin in a PPARgamma-dependent manner. We propose that activation of PPARgamma in myocytes induces a local production of adiponectin that acts on muscle tissue to improve insulin sensitivity.

Curcumin, a compound found in the spice turmeric, has been shown to possess a number of beneficial biological activities exerted through a variety of different mechanisms. Some curcumin effects have been reported to involve activation of the nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPAR-γ), but the concept that curcumin might be a PPAR-γ ligand remains controversial. Results reported here demonstrate that, in contrast to the PPAR-γ ligands ciglitazone and rosiglitazone, curcumin is inactive in five different reporter or DNA-binding assays, does not displace [(3)H]rosiglitazone from the PPAR-γ ligand-binding site, and does not induce PPAR-γ-dependent differentiation of preadipocytes, while its ability to inhibit fibroblast-to-myofibroblast differentiation is not affected by any of four PPAR-γ antagonists. These multiple lines of evidence conclusively demonstrate that curcumin is not a PPAR-γ ligand and indicate the need for further investigation of the mechanisms through which the compound acts.

Objective: To evaluate the effectiveness and safety of pioglitazone therapy in a patient with an atypical presentation of partial lipodystrophy., Methods: We present a case report and review the associated literature to put this case in perspective and explain its atypical features., Results: A 40-year-old woman was referred because of uncontrolled diabetes and dyslipidemia, despite receiving a total daily dose of insulin of 300 U and combination therapy with a statin and a fibrate. On examination, the patient was found to have substantial central and abdominal fat deposition in conjunction with slender arms and legs. The addition of pioglitazone to her therapeutic regimen resulted in a dramatic improvement in glycemic control and in the dyslipidemia. During approximately a 2-year period, the patient's insulin dose was decreased and was ultimately discontinued. Considerable increases in weight and in waist circumference were observed during this period. Sequencing of candidate genes known to be associated with familial partial lipodystrophy, acquired partial lipodystrophy, and generalized lipodystrophy showed no genetic abnormalities. Magnetic resonance imaging confirmed the presence of significant visceral and subcutaneous abdominal fat deposition, in association with scant fat tissue in the extremities. Her weight decreased after discontinuation of the insulin therapy and institution of dietary counseling., Conclusion: Thiazolidinediones have been shown to be efficacious in syndromic lipodystrophies, such as familial partial lipodystrophy subtype 2. We report that these pharmaceutical agents may also help improve metabolic variables in atypical lipodystrophy syndromes with no obvious molecular basis. A pronounced weight gain might result from synergism between thiazolidinediones and insulin promoting adipogenesis, which diminished somewhat after discontinuation of insulin therapy.

Context: Familial partial lipodystrophy (FPLD) results from coding sequence mutations either in LMNA, encoding nuclear lamin A/C, or in PPARG, encoding peroxisome proliferator-activated receptor-gamma (PPARgamma). The LMNA form is called FPLD2 (MIM 151660) and the PPARG form is called FPLD3 (MIM 604367)., Objective: Our objective was to investigate whether the clinical phenotype of this proband is due to mutation(s) in PPARgamma., Design: This is a case report. Patient and Setting: A 31-yr-old female with the clinical phenotype of FPLD3, i.e. lipodystrophy and early childhood diabetes with extreme insulin resistance and hypertriglyceridemia leading to recurrent pancreatitis, was assessed at an academic medical center., Results: The proband was heterozygous for a novel C-->T mutation in the PPARG gene that led to the substitution of arginine 194 in PPARgamma2 isoform, a conserved residue located in the zinc finger structure involved in DNA binding, by tryptophan (R194W). The mutation was absent from the genomes of 100 healthy Caucasians. In vitro analysis of the mutated protein showed that R194W (and R166W in PPARgamma1 isoform) could not bind to DNA and had no transcriptional activity. Furthermore, R194W had no dominant-negative activity., Conclusions: The R194W mutation in PPARG disrupts its DNA binding activity and through haploinsufficiency leads to clinical manifestation of FPLD3 and the associated metabolic disturbances.

The transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma) plays an important role in regulating lipid and glucose metabolism and improves insulin sensitivity in diabetic patients when activated by thiazolidinedione drugs. Several loss-of-function mutations in PPARgamma have been identified that cause lipodystrophy and diabetes in humans. Because affected individuals are heterozygotes and have one normal PPARgamma allele, it is of interest to know whether these mutations act in a dominant-negative fashion to inhibit the activity of the wild-type (WT) receptor. Here we compare the molecular phenotypes of two previously identified PPARgamma mutations: P467L, reported to be dominant negative; and F388L, reported to be devoid of dominant-negative activity. We developed a competitive chromatin immunoprecipitation assay to measure the relative ability of mutant PPARgamma to compete with WT receptor for binding to a PPAR regulatory element (PPRE)-containing promoter. By determining the ratio of mutant and WT receptors bound to a PPRE over time, we estimated the relative promoter turnover rate of each receptor. This assay demonstrated that PPARgamma bearing the P467L had a reduced promoter turnover rate compared with the F388L receptor, and over time out-competed the WT receptor for promoter binding sites. We propose that the P467L receptor is dominant negative because in a cell containing both WT and mutant receptors, the majority of the PPAR-regulated promoters will be occupied by the transcriptionally defective mutant receptor. In contrast, the F388L mutation lacks dominant-negative activity because its more rapid promoter turnover rate prevented it from out-competing the WT receptor for promoter binding sites.

Lipodystrophy and insulin resistance are the core features of human PPARgamma deficiency states. Metabolic complications in PPARgamma deficiency, such as hypertension, have been considered to be secondary to insulin resistance. However, a new mouse model that expresses the analog of a human PPARG mutation displays minimal lipodystrophy and insulin resistance but rather severe hypertension. Furthermore, the mutant protein appears to directly modulate the renin-angiotensin system in adipose tissue, providing evidence of the pleiotropic effects of PPARgamma.

Since its identification as the receptor for antidiabetic thiazolidinedione drugs, peroxisome proliferator-activated receptor-gamma (PPARgamma) has been the focus of pharmaceutical drug discovery programs directed toward finding better drugs for the treatment of diabetes, as well as the object of basic research aimed at understanding its role in the regulation of metabolism. We now understand a great deal about the crucial role that PPARgamma plays in adipocyte differentiation and development, and are rapidly gaining knowledge about the role of the receptor in the regulation of metabolism. However, many crucial aspects of the molecular mechanism by which modulation of PPARgamma activity affects insulin resistance and glucose homeostasis are still not clearly understood. Here the authors review the current status of PPARgamma research, with an emphasis on its role in the causes and treatment of type 2 diabetes.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor family of ligand-dependent transcription factors, is a critical regulator of adipocyte differentiation and glucose metabolism. The expression, regulation, and functional significance of PPAR-gamma in alveolar macrophages (AMs), the predominant resident immune effector cell within the alveolus, have not been previously examined. In this study, we show that, in contrast to peritoneal macrophages, resident murine AMs constitutively express high levels of PPAR-gamma. Expression was primarily located in the nucleus by immunofluorescence staining. Quantitative real-time RT-PCR demonstrated that the predominant isoform was PPAR-gamma2. Expression of PPAR-gamma was induced by the anti-inflammatory cytokine IL-4. Treatment of murine AMs with PPAR-gamma ligands suppresses PMA-stimulated oxidative burst activity and LPS + IFN-gamma-mediated expression of inducible nitric oxide synthase. In addition, LPS-induced IL-12 mRNA and protein expression was inhibited by PPAR-gamma ligands. These results support an important immunomodulatory role for PPAR-gamma in AM responses.

AMP-activated protein kinase (AMPK) is the central component of a cellular signaling system that regulates multiple metabolic enzymes and pathways in response to reduced intracellular energy levels. The transcription factor hepatic nuclear factor 4alpha (HNF4alpha) is an orphan nuclear receptor that regulates the expression of genes involved in energy metabolism in the liver, intestine, and endocrine pancreas. Inheritance of a single null allele of HNF4alpha causes diabetes in humans. Here we demonstrate that AMPK directly phosphorylates HNF4alpha and represses its transcriptional activity. AMPK-mediated phosphorylation of HNF4alpha on serine 304 had a 2-fold effect, reducing the ability of the transcription factor to form homodimers and bind DNA and increasing its degradation rate in vivo. These results demonstrate that HNF4alpha is a downstream target of AMPK and raise the possibility that one of the effects of AMPK activation is reduced expression of HNF4alpha target genes.

Autosomal dominant familial partial lipodystrophy (FPLD) due to mutant LMNA encoding nuclear lamin A/C is characterized by adipose tissue repartitioning together with multiple metabolic disturbances, including insulin resistance and dyslipidemia. There is emerging evidence that some rare mutations in peroxisome proliferator-activated receptor-gamma (PPAR-gamma), encoded by PPARG, might be associated with human lipodystrophy. We report a three-generation Canadian kindred ascertained based upon partial lipodystrophy, with a normal LMNA gene sequence. Candidate gene sequencing showed that all four affected subjects were heterozygous for a novel T-->A mutation at PPARG nucleotide 1164 in exon 5 that predicted substitution of phenylalanine at codon 388 by leucine (F388L). The mutation was absent from normal family members and normal unrelated subjects, and altered a highly conserved residue within helix 8 of the predicted ligand-binding pocket of PPAR-gamma. The mutant receptor had significantly decreased basal transcriptional activity and impaired stimulation by a synthetic ligand. The germline transmission of a transactivation-deficient mutation in PPARG suggests that autosomal dominant partial lipodystrophy is genetically heterogeneous. Our findings are consistent with the idea that mutant PPARG can underlie the partial lipodystrophy phenotype.