Monogenic forms of insulin resistance: apertures that expose the common metabolic syndrome

Liver transplantation in patient with Berardinelli-Seip syndrome: A literature review and case report

BACKGROUND

Berardinelli-Seip syndrome is an infrequently seen and potentially fatal genetic disorder characterized by the absence of adipose tissue. Herein, we report a first-in-literature liver transplant done on a 7-year-old girl because of liver cirrhosis caused by the Berardinelli-Seip syndrome.

CASE REPORT

Physical examination showed prominent subdermal fat tissue loss and mild muscle hypertrophy, giving her a slim appearance, hirsutism, thick hair, a large head in contrast to the body, low anterior hairline, icterus, prominent facial contours, prominent mandibula, loss of buccal fat, low set ears, and large limbs. After the diagnosis, she admitted to our clinic because of variceal esophageal bleeding and increasing liver enzymes. Transplantation decision was made and orthothopic liver transplantation done by the surgery team.

DISCUSSION

Common causes of death in Berardinelli-Seip syndrome patients are infections and liver cirrhosis. The mean age of the patients was 27.1 at the time of death. There is no any established cure for congenital lipodystrophies so far. However, some symptomatic treatment methods are found to be helpful. The main point of the case report to be discussed is the liver transplantation done by our surgical team. There are no examples of any transplantation in Berardinelli-Seip syndrome patients, but several reports can be found of patients with kidney or liver failure.

CONCLUSION

Berardinelli-Seip syndrome is a rare disorder with no cure but a chance of improving lifestyle and life expectancy. The transplantation option should be considered in young patients after a multidisciplinary review.

Modification of the structural stability of human serum albumin in rheumatoid arthritis

Differential scanning calorimetry (DSC) can indicate changes in structure and/or concentration of the most abundant proteins in a biological sample via heat denaturation curves (HDCs). In blood serum for example, HDC changes result from either concentration changes or altered thermal stabilities for 7-10 proteins and has previously been shown capable of differentiating between sick and healthy human subjects. Here, we compare HDCs and proteomic profiles of 50 patients experiencing joint-inflammatory symptoms, 27 of which were clinically diagnosed with rheumatoid arthritis (RA). The HDC of all 50 subjects appeared significantly different from expected healthy curves, but comparison of additional differences between the RA and the non-RA subjects allowed more specific understanding of RA samples. We used mass spectrometry (MS) to investigate the reasons behind the additional HDC changes observed in RA patients. The HDC differences do not appear to be directly related to differences in the concentrations of abundant serum proteins. Rather, the differences can be attributed to modified thermal stability of some fraction of the human serum albumin (HSA) proteins in the sample. By quantifying differences in the frequency of artificially induced post translational modifications (PTMs), we found that HSA in RA subjects had a much lower surface accessibility, indicating potential ligand or protein binding partners in certain regions that could explain the shift in HSA melting temperature in the RA HDCs. Several low abundance proteins were found to have significant changes in concentration in RA subjects and could be involved in or related to binding of HSA. Certain amino acid sites clusters were found to be less accessible in RA subjects, suggesting changes in HSA structure that may be related to changes in protein-protein interactions. These results all support a change in behavior of HSA which may give insight into mechanisms of RA pathology.

Role of Actionable Genes in Pursuing a True Approach of Precision Medicine in Monogenic Diabetes

Monogenic diabetes is a genetic disorder caused by one or more variations in a single gene. It encompasses a broad spectrum of heterogeneous conditions, including neonatal diabetes, maturity onset diabetes of the young (MODY) and syndromic diabetes, affecting 1-5% of patients with diabetes. Some of these variants are harbored by genes whose altered function can be tackled by specific actions ("actionable genes"). In suspected patients, molecular diagnosis allows the implementation of effective approaches of precision medicine so as to allow individual interventions aimed to prevent, mitigate or delay clinical outcomes. This review will almost exclusively concentrate on the clinical strategy that can be specifically pursued in carriers of mutations in "actionable genes", including ABCC8, KCNJ11, GCK, HNF1A, HNF4A, HNF1B, PPARG, GATA4 and GATA6. For each of them we will provide a short background on what is known about gene function and dysfunction. Then, we will discuss how the identification of their mutations in individuals with this form of diabetes, can be used in daily clinical practice to implement specific monitoring and treatments. We hope this article will help clinical diabetologists carefully consider who of their patients deserves timely genetic testing for monogenic diabetes.

Monogenic diabetes: a gateway to precision medicine in diabetes

Monogenic diabetes refers to diabetes mellitus (DM) caused by a mutation in a single gene and accounts for approximately 1%-5% of diabetes. Correct diagnosis is clinically critical for certain types of monogenic diabetes, since the appropriate treatment is determined by the etiology of the disease (e.g., oral sulfonylurea treatment of HNF1A/HNF4A-diabetes vs. insulin injections in type 1 diabetes). However, achieving a correct diagnosis requires genetic testing, and the overlapping of the clinical features of monogenic diabetes with those of type 1 and type 2 diabetes has frequently led to misdiagnosis. Improvements in sequencing technology are increasing opportunities to diagnose monogenic diabetes, but challenges remain. In this Review, we describe the types of monogenic diabetes, including common and uncommon types of maturity-onset diabetes of the young, multiple causes of neonatal DM, and syndromic diabetes such as Wolfram syndrome and lipodystrophy. We also review methods of prioritizing patients undergoing genetic testing, and highlight existing challenges facing sequence data interpretation that can be addressed by forming collaborations of expertise and by pooling cases.

Unusual Glycemic Presentations in a Child with a Novel Heterozygous Intragenic INSR Deletion

BACKGROUND

Mutations of the insulin receptor (INSR) gene lead to a wide spectrum of inherited insulin resistance (IR) syndromes. Among these, type A-IR, usually caused by dominant negative INSR mutations, generally presents peri-pubertally in girls.

CASE

A 2.8-year-old girl was referred due to recurrent postprandial and fasting hypoglycemia. She had been born at full-term with birth weight 1.89 kg, and had developed transient neonatal diabetes. Examination showed satisfactory growth, reduced adipose tissue, acanthosis nigricans, and isolated thelarche. After 12 h of fasting, she developed hypoglycemia (glucose 2.8 mmol/L), with inappropriately raised plasma insulin concentration of 5.4 mU/L and suppressed fatty acids and ketone bodies. Oral glucose tolerance testing showed severely increased plasma insulin concentration (>300 mU/L) with hypoglycemia (glucose 1.6 mmol/L) at 2.5 h. She was initially managed on dietary modifications, cornstarch, and then trialed on acarbose for postprandial hyperinsulinemic hypoglycemia (PPHH) with some response. However, she was noted to have increased frequency of hyperglycemia after a couple of years of treatment. She was then switched to metformin and continued to have dietary carbohydrate modification including cornstarch that improved fasting tolerance, hyperglycemia, and postprandial hypoglycemia. Genetic testing identified heterozygous deletion of the last exon of the INSR gene, exon 22.

CONCLUSION

We present a case of type A-IR, caused by a novel INSR deletion, presenting unusually early with transient neonatal diabetes, followed by episodes of hypoglycemia and hyperglycemia during later childhood. Early life presentations, including neonatal diabetes and PPHH, should lead to consideration of type A-IR.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

Structural Basis and Genotype-Phenotype Correlations of INSR Mutations Causing Severe Insulin Resistance

The insulin receptor (INSR) gene was analyzed in four patients with severe insulin resistance, revealing five novel mutations and a deletion that removed exon 2. A patient with Donohue syndrome (DS) had a novel p.V657F mutation in the second fibronectin type III domain (FnIII-2), which contains the α-β cleavage site and part of the insulin-binding site. The mutant INSR was expressed in Chinese hamster ovary cells, revealing that it reduced insulin proreceptor processing and impaired activation of downstream signaling cascades. Using online databases, we analyzed 82 INSR missense mutations and demonstrated that mutations causing DS were more frequently located in the FnIII domains than those causing the milder type A insulin resistance (P = 0.016). In silico structural analysis revealed that missense mutations predicted to severely impair hydrophobic core formation and stability of the FnIII domains all caused DS, whereas those predicted to produce localized destabilization and to not affect folding of the FnIII domains all caused the less severe Rabson-Mendenhall syndrome. These results suggest the importance of the FnIII domains, provide insight into the molecular mechanism of severe insulin resistance, will aid early diagnosis, and will provide potential novel targets for treating extreme insulin resistance.

Review: The metabolic syndrome as an endocrine disease: is there an effective pharmacotherapeutic strategy optimally targeting the pathogenesis?

The metabolic syndrome (MetS) represents a combination of cardiovascular risk determinants such as obesity, insulin resistance and lipid abnormalities such as hypertriglyceridemia, increased free fatty acids, low high-density-cholesterol and hypertension. As a multiple component condition it imparts a doubling of relative risk for atherosclerotic cardiovascular disease (ASCVD). It is currently controversial which component of the syndrome carries what weight. There is even a considerable debate whether the risk for ASCVD is greater in patients diagnosed with MetS than that by the individual risk factors. At present, no unifying pathogenetic mechanism can explain the metabolic syndrome and there is no unique treatment for it. This review summarizes and critically reviews the currently available clinical and scientific evidence for the concept that the MetS is causally an endocrine disease and discusses pharmacotherapeutic strategies targeting the pathogenesis rather than single symptoms of the cluster.

Identification and Functional Characterization of Two Novel Nonsense Mutations in the β-Subunit of INSR That Cause Severe Insulin Resistance Syndrome

BACKGROUND/AIMS

Donohue syndrome is an extremely rare autosomal recessive disorder caused by mutations in INSR. This study describes the clinical course of a patient with Donohue syndrome, and we also evaluated the molecular and functional characteristics of 2 novel INSR mutations.

METHODS

Our patient was a male newborn with acanthosis nigricans, lack of subcutaneous fat, hirsutism, thick lips, and high serum insulin levels, all of which are characteristic of Donohue syndrome. INSR mutation analysis was performed, and Western blot analysis was used to verify the effects of the novel mutations on INSR protein expression.

RESULTS

Direct INSR sequencing identified the following 2 novel compound heterozygous mutations in the β-subunit of INSR: p.Arg1066* and p.Gln1232*. Western blot analysis of skin fibroblasts revealed a comparable expression of the α-subunit of INSR in mutant and control samples, but reduced levels of mature INSR β-subunit protein were found in mutant INSR-expressing cells in comparison to the controls.

CONCLUSIONS

This study describes the clinical course of a male patient with Donohue syndrome and the molecular characteristics of 2 novel compound heterozygous mutations in INSR. These novel nonsense mutations are associated with reduced expression of the mature INSR β-subunit, which was most likely due to impaired proreceptor processing.

A novel homozygous missense mutation in the insulin receptor gene results in an atypical presentation of Rabson-Mendenhall syndrome

Leprechaunism (Donohue syndrome) and Rabson-Mendenhall syndrome are caused by mutations in the insulin receptor gene and are associated with extreme insulin resistance. Clinically these syndromes appear to represent points on a continuum of severity of receptor dysfunction, rather than completely distinct syndromes. We investigated a Libyan infant with growth retardation, facial dysmorphism (elfin-like features), acanthosis nigricans and hirsutism. Fasting hypoglycaemia and postprandial hyperglycaemia with persistent hyperinsulinemia were found. A novel homozygous missense mutation was found in exon 2, resulting in a substitution of a glycine-132 for a serine in the INSR α-subunit (c.394G > A; p.Gly132Ser). At age ten, he developed diabetes mellitus. At age eleven, patient is still alive with mental retardation and severe growth retardation.

New insights from monogenic diabetes for "common" type 2 diabetes

Boundaries between monogenic and complex genetic diseases are becoming increasingly blurred, as a result of better understanding of phenotypes and their genetic determinants. This had a large impact on the way complex disease genetics is now being investigated. Starting with conventional approaches like familial linkage, positional cloning and candidate genes strategies, the scope of complex disease genetics has grown exponentially with scientific and technological advances in recent times. Despite identification of multiple loci harboring common and rare variants associated with complex diseases, interpreting and evaluating their functional role has proven to be difficult. Information from monogenic diseases, especially related to the intermediate traits associated with complex diseases comes handy. The significant overlap between traits and phenotypes of monogenic diseases with related complex diseases provides a platform to understand the disease biology better. In this review, we would discuss about one such complex disease, type 2 diabetes, which shares marked similarity of intermediate traits with different forms of monogenic diabetes.

11β-Hydroxysteroid dehydrogenase type 1 shRNA ameliorates glucocorticoid-induced insulin resistance and lipolysis in mouse abdominal adipose tissue

Long-term glucocorticoid exposure increases the risk for developing type 2 diabetes. Prereceptor activation of glucocorticoid availability in target tissue by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) coupled with hexose-6-phosphate dehydrogenase (H6PDH) is an important mediator of the metabolic syndrome. We explored whether the tissue-specific modulation of 11β-HSD1 and H6PDH in adipose tissue mediates glucocorticoid-induced insulin resistance and lipolysis and analyzed the effects of 11β-HSD1 inhibition on the key lipid metabolism genes and insulin-signaling cascade. We observed that corticosterone (CORT) treatment increased expression of 11β-HSD1 and H6PDH and induced lipase HSL and ATGL with suppression of p-Thr(172) AMPK in adipose tissue of C57BL/6J mice. In contrast, CORT induced adipose insulin resistance, as reflected by a marked decrease in IR and IRS-1 gene expression with a reduction in p-Thr(308) Akt/PKB. Furthermore, 11β-HSD1 shRNA attenuated CORT-induced 11β-HSD1 and lipase expression and improved insulin sensitivity with a concomitant stimulation of pThr(308) Akt/PKB and p-Thr(172) AMPK within adipose tissue. Addition of CORT to 3T3-L1 adipocytes enhanced 11β-HSD1 and H6PDH and impaired p-Thr(308) Akt/PKB, leading to lipolysis. Knockdown of 11β-HSD1 by shRNA attenuated CORT-induced lipolysis and reversed CORT-mediated inhibition of pThr(172) AMPK, which was accompanied by a parallel improvement of insulin signaling response in these cells. These findings suggest that elevated adipose 11β-HSD1 expression may contribute to glucocorticoid-induced insulin resistance and adipolysis.

New opportunities: harnessing induced pluripotency for discovery in diabetes and metabolism

The landmark discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka has transformed regenerative biology. Previously, insights into the pathogenesis of chronic human diseases have been hindered by the inaccessibility of patient samples. However, scientists are now able to convert patient fibroblasts into iPSCs and differentiate them into disease-relevant cell types. This ability opens new avenues for investigating disease pathogenesis and designing novel treatments. In this review, we highlight the uses of human iPSCs to uncover the underlying causes and pathological consequences of diabetes and metabolic syndromes, multifactorial diseases whose etiologies have been difficult to unravel using traditional methodologies.

Adipokines mediate inflammation and insulin resistance

For many years, adipose tissue was considered as an inert energy storage organ that accumulates and stores triacylglycerols during energy excess and releases fatty acids in times of systemic energy need. However, over the last two decades adipose tissue depots have been established as highly active endocrine and metabolically important organs that modulate energy expenditure and glucose homeostasis. In rodents, brown adipose tissue plays an essential role in non-shivering thermogenesis and in energy dissipation that can serve to protect against diet-induced obesity. White adipose tissue collectively referred too as either subcutaneous or visceral adipose tissue is responsible for the secretion of an array of signaling molecules, termed adipokines. These adipokines function as classic circulating hormones to communicate with other organs including brain, liver, muscle, the immune system, and adipose tissue itself. The dysregulation of adipokines has been implicated in obesity, type 2 diabetes, and cardiovascular disease. Recently, inflammatory responses in adipose tissue have been shown as a major mechanism to induce peripheral tissue insulin resistance. Although leptin and adiponectin regulate feeding behavior and energy expenditure, these adipokines are also involved in the regulation of inflammatory responses. Adipose tissue secretes various pro- and anti-inflammatory adipokines to modulate inflammation and insulin resistance. In obese humans and rodent models, the expression of pro-inflammatory adipokines is enhanced to induce insulin resistance. Collectively, these findings have suggested that obesity-induced insulin resistance may result, at least in part, from an imbalance in the expression of pro- and anti-inflammatory adipokines. Thus we will review the recent progress regarding the physiological and molecular functions of adipokines in the obesity-induced inflammation and insulin resistance with perspectives on future directions.

Hyperinsulinemia drives diet-induced obesity independently of brain insulin production

Hyperinsulinemia is associated with obesity and pancreatic islet hyperplasia, but whether insulin causes these phenomena or is a compensatory response has remained unsettled for decades. We examined the role of insulin hypersecretion in diet-induced obesity by varying the pancreas-specific Ins1 gene dosage in mice lacking Ins2 gene expression in the pancreas, thymus, and brain. Age-dependent increases in fasting insulin and β cell mass were absent in Ins1(+/-):Ins2(-/-) mice fed a high-fat diet when compared to Ins1(+/+):Ins2(-/-) littermate controls. Remarkably, Ins1(+/-):Ins2(-/-) mice were completely protected from diet-induced obesity. Genetic prevention of chronic hyperinsulinemia in this model reprogrammed white adipose tissue to express uncoupling protein 1 and increase energy expenditure. Normalization of adipocyte size and activation of energy expenditure genes in white adipose tissue was associated with reduced inflammation, reduced fatty acid spillover, and reduced hepatic steatosis. Thus, we provide genetic evidence that pathological circulating hyperinsulinemia drives diet-induced obesity and its complications.

Epigenetic manifestation of metabolic syndrome and dietary management

SIGNIFICANCE

Metabolic syndrome constitutes a group of disorders such as insulin resistance, hypertension, and hypertriglyceridemia, predisposing an individual to risk factors such as cardiovascular disease, diabetes, obesity, and dyslipidemia. A majority of these diseases are influenced by the environmental factors, nutrient uptake, and genetic profile of an individual that together dysregulate gene function. These genetic and nongenetic factors are reported to introduce epigenetic cues that modulate the gene function which is inherited by the offspring.

RECENT ADVANCES

Considering the epigenetic modulation of the metabolic disorders, nutrigenomics has been distinctly categorized as a branch that deals with modulatory effect of nutrients on metabolic disorders and disease progression by supplementing the individuals with key nutrient-enriched diets which are derived from plant and animal sources.

CRITICAL ISSUES

Nutritional components of the diet regulate the metabolic health of an individual either by controlling the expression of some key genes related to metabolic pathways or by modulating the epigenetic events on such genes. The present article discusses various metabolic disorders in detail and the effect of nutrients on the specific genes causing those disorders. We also highlight the molecular mechanisms of some metabolic disorders through epigenetic modifications and possible therapeutic interventions.

FUTURE DIRECTIONS

With the advent of high-throughput technologies and epigenetic modulation of the metabolic disorders, an altered epigenetic code that is programmed due to improper nutrients can be reverted back by supplementing the diet with various plant-derived compounds. The implication of small molecular drugs is also of utmost significance for challenging the metabolic disorders.

Sp1 transcription factor interaction with accumulated prelamin a impairs adipose lineage differentiation in human mesenchymal stem cells: essential role of sp1 in the integrity of lipid vesicles

Lamin A (LMNA)-linked lipodystrophies may be either genetic (associated with LMNA mutations) or acquired (associated with the use of human immunodeficiency virus protease inhibitors [PIs]), and in both cases they share clinical features such as anomalous distribution of body fat or generalized loss of adipose tissue, metabolic alterations, and early cardiovascular complications. Both LMNA-linked lipodystrophies are characterized by the accumulation of the lamin A precursor prelamin A. The pathological mechanism by which prelamin A accumulation induces the lipodystrophy associated phenotypes remains unclear. Since the affected tissues in these disorders are of mesenchymal origin, we have generated an LMNA-linked experimental model using human mesenchymal stem cells treated with a PI, which recapitulates the phenotypes observed in patient biopsies. This model has been demonstrated to be a useful tool to unravel the pathological mechanism of the LMNA-linked lipodystrophies, providing an ideal system to identify potential targets to generate new therapies for drug discovery screening. We report for the first time that impaired adipogenesis is a consequence of the interaction between accumulated prelamin A and Sp1 transcription factor, sequestration of which results in altered extracellular matrix gene expression. In fact, our study shows a novel, essential, and finely tuned role for Sp1 in adipose lineage differentiation in human mesenchymal stem cells. These findings define a new physiological experimental model to elucidate the pathological mechanisms LMNA-linked lipodystrophies, creating new opportunities for research and treatment not only of LMNA-linked lipodystrophies but also of other adipogenesis-associated metabolic diseases.

Yin and Yang of hypothalamic insulin and leptin signaling in regulating white adipose tissue metabolism

Fatty acids released from white adipose tissue (WAT) provide important energy substrates during fasting. However, uncontrolled fatty acid release from WAT during non-fasting states causes lipotoxicity and promotes inflammation and insulin resistance, which can lead to and worsen type 2 diabetes (DM2). WAT is also a source for insulin sensitizing fatty acids such as palmitoleate produced during de novo lipogenesis. Insulin and leptin are two major hormonal adiposity signals that control energy homeostasis through signaling in the central nervous system. Both hormones have been implicated to regulate both WAT lipolysis and de novo lipogenesis through the mediobasal hypothalamus (MBH) in an opposing fashion independent of their respective peripheral receptors. Here, we review the current literature on brain leptin and insulin action in regulating WAT metabolism and discuss potential mechanisms and neuro-anatomical substrates that could explain the opposing effects of central leptin and insulin. Finally, we discuss the role of impaired hypothalamic control of WAT metabolism in the pathogenesis of insulin resistance, metabolic inflexibility and type 2 diabetes.

Insulin resistance in obesity as the underlying cause for the metabolic syndrome

The metabolic syndrome affects more than a third of the US population, predisposing to the development of type 2 diabetes and cardiovascular disease. The 2009 consensus statement from the International Diabetes Federation, American Heart Association, World Heart Federation, International Atherosclerosis Society, International Association for the Study of Obesity, and the National Heart, Lung, and Blood Institute defines the metabolic syndrome as 3 of the following elements: abdominal obesity, elevated blood pressure, elevated triglycerides, low high-density lipoprotein cholesterol, and hyperglycemia. Many factors contribute to this syndrome, including decreased physical activity, genetic predisposition, chronic inflammation, free fatty acids, and mitochondrial dysfunction. Insulin resistance appears to be the common link between these elements, obesity and the metabolic syndrome. In normal circumstances, insulin stimulates glucose uptake into skeletal muscle, inhibits hepatic gluconeogenesis, and decreases adipose-tissue lipolysis and hepatic production of very-low-density lipoproteins. Insulin signaling in the brain decreases appetite and prevents glucose production by the liver through neuronal signals from the hypothalamus. Insulin resistance, in contrast, leads to the release of free fatty acids from adipose tissue, increased hepatic production of very-low-density lipoproteins and decreased high-density lipoproteins. Increased production of free fatty acids, inflammatory cytokines, and adipokines and mitochondrial dysfunction contribute to impaired insulin signaling, decreased skeletal muscle glucose uptake, increased hepatic gluconeogenesis, and β cell dysfunction, leading to hyperglycemia. In addition, insulin resistance leads to the development of hypertension by impairing vasodilation induced by nitric oxide. In this review, we discuss normal insulin signaling and the mechanisms by which insulin resistance contributes to the development of the metabolic syndrome.

Brain insulin controls adipose tissue lipolysis and lipogenesis

White adipose tissue (WAT) dysfunction plays a key role in the pathogenesis of type 2 diabetes (DM2). Unrestrained WAT lipolysis results in increased fatty acid release, leading to insulin resistance and lipotoxicity, while impaired de novo lipogenesis in WAT decreases the synthesis of insulin-sensitizing fatty acid species like palmitoleate. Here, we show that insulin infused into the mediobasal hypothalamus (MBH) of Sprague-Dawley rats increases WAT lipogenic protein expression, inactivates hormone-sensitive lipase (Hsl), and suppresses lipolysis. Conversely, mice that lack the neuronal insulin receptor exhibit unrestrained lipolysis and decreased de novo lipogenesis in WAT. Thus, brain and, in particular, hypothalamic insulin action play a pivotal role in WAT functionality.

Functional characterization of insulin receptor gene mutations contributing to Rabson-Mendenhall syndrome - phenotypic heterogeneity of insulin receptor gene mutations

Rabson-Mendenhall syndrome (RMS) is a rare disorder that presents as severe insulin resistance as a result of mutations present in the insulin receptor (INSR). A Chinese girl with RMS presented with profound diabetes, hyperinsulinemia, acanthosis nigricans, hirsutism, and abnormalities of teeth and nails. Direct sequencing of the patient's INSR detected heterozygote mutations at Arg83Gln (R83Q) and Ala1028Val (A1028V), with the former representing a novel mutation. Functional studies of Chinese hamster ovary (CHO) cells transfected with wild-type (WT) and mutant forms of INSR were performed to evaluate the effects of these mutations on receptor expression and activation. Receptor expression, insulin binding activity, and phosphorylation of the R83Q variant were comparable to WT. In contrast, expression of the A1028V receptor was much lower than that of WT INSR, and impairment of insulin binding and autophosphorylation were nearly commensurate with the decrease in expression detected. Reductions in the phosphorylation of IRS-1, Akt, and Erk1/2 (60%, 40%, and 50% of WT, respectively) indicate that the A1028V receptor contributes to impaired signal transduction. In conclusion, INSR mutations associated with RMS were identified. Moreover, the A1028V mutation associated with a decrease in expression of INSR potentially accounts for loss of function of the INSR.

Clinical approach to the patient with diabetes mellitus and very high insulin requirements

A number of patients with diabetes require very high (> 2 Ukg⁻¹ day⁻¹), or extremely high (> 3 Ukg⁻¹ day⁻¹), insulin doses for the management of their hyperglycemia. Unfortunately, many of the physicians who treat these patients limit themselves to prescribing ever higher doses of insulin, without questioning why. Furthermore, when the insulin requirements get to be extreme, demanding an explanation, clinicians are frequently lost in a sea of literature where there is not a single paper dealing with this problem systematically. A systematic approach to the evaluation of these patients is necessary to facilitate an appropriate diagnosis, select the most reasonable therapy, and hopefully improve the long-term outcome of these patients. This manuscript intends to provide the clinician with a review of the literature pertinent for the differential diagnosis, work-up, and management of these patients. We will review the definitions of insulin sensitivity during normality, the various degrees or categories of insulin resistance, and the expected insulin requirements during each of these states. Subsequently, we propose a simple alphabetic mnemonic approach to help remember the differential diagnosis, and a clinical algorithm to help guide the work-up of these patients. Lastly, we briefly discuss general management considerations in these conditions.

A promoter polymorphism of lamin A/C gene is an independent genetic predisposition to arterial stiffness in a Japanese general population (the Tanno and Sobetsu study)

AIM

We examined the hypothesis that there is a positive, independent association between polymorphisms of lamin A/C gene (LMNA) and arterial stiffness in Japanese.

METHODS

The subjects were 261 men (mean age, 64.4+/-0.7 years) selected from inhabitants of the towns of Tanno and Sobetsu in a rural area of Japan who underwent medical check-ups. We conducted clinical examinations, including measurement of bilateral brachial-ankle pulse wave velocity (baPWV) as a marker of arterial stiffness, and genetic analysis. Subjects with atrial fibrillation, subjects with ankle-brachial index <0.9, and subjects taking any medication were excluded. We selected two single nucleotide polymorphisms (SNPs) as markers of LMNA, 1908C/T in exon 10 and -1030C/T in the promoter region, which we have recently identified. All genotypes were clearly determined by the TaqMan PCR method.

RESULTS

Genotype frequencies of the two polymorphisms satisfied the Hardy-Weinberg equilibrium. The baPWV of -1030C/T polymorphism was significantly greater in subjects with CC genotype than in subjects with CT+TT genotype (1,652+/-22.1 cm/s vs. 1,552+/-43.0 cm/s, p=0.039); however, no significant difference was found for 1908C/T polymorphism. The baPWV was found to be significantly associated with age, body height, systolic blood pressure, and smoking habit; therefore, we next performed multiple regression analysis including these parameters, and found an independent, significant association between baPWV and -1030C/T polymorphism.

CONCLUSION

Promoter -1030C/T polymorphism of LMNA is a possible genetic predisposition to arterial stiffness in the Japanese population.

A case of Dunnigan-type familial partial lipodystrophy (FPLD) due to lamin A/C (LMNA) mutations complicated by end-stage renal disease

Dunnigan-type familial partial lipodystrophy (FPLD) is a rare monogenic adipose tissue disorder in which the affected subjects have increased predisposition to insulin resistance and related metabolic complications, such as glucose intolerance, diabetes, dyslipidemia, and hepatic steatosis. Our patient was a 35-year-old female who had been receiving insulin injection therapy for diabetes mellitus and was transferred to our hospital. She was diagnosed with FPLD on the basis of the following symptoms: increase in subcutaneous fat in the face, neck, and upper trunk; loss of subcutaneous fat in the lower limbs and the gluteal region. We found a heterozygous CGG to CAG transition in codon 482 of exon 8 in the gene encoding lamin A/C (LMNA), which leads to an arginine to glutamine substitution (R482Q). At the time of admission, her serum creatinine level was 8.4 mg/dl, and her blood urea nitrogen (BUN) level was 81 mg/dl. Her serum creatinine level was elevated and hemodialysis was performed twice every week. However, she died of cerebral hemorrhage 9 months after hemodialysis. Although it is uncommon for patients with FPLD to exhibit renal dysfunction and require hemodialysis, this case suggests the need for careful analysis of renal function in a patient with FPLD.

Lipin1 is a key factor for the maturation and maintenance of adipocytes in the regulatory network with CCAAT/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma 2

Lipin1 expression was induced at a late stage of differentiation of 3T3-L1 preadipocytes and maintained at high levels in mature adipocytes. Knockdown of expression of lipin1 by small interfering RNA in 3T3-L1 preadipocytes almost completely inhibited differentiation into adipocytes, whereas overexpression of lipin1 accelerated adipocyte differentiation, demonstrating that lipin1 is required for adipocyte differentiation. In mature adipocytes, transfection of lipin1-small interfering RNA decreased the expression of adipocyte functional genes, indicating the involvement of lipin1 in the maintenance of adipocyte function. Lipin1 increases the transcription-activating function of peroxisome proliferator-activated receptor gamma(2) (PPAR gamma(2)) via direct physical interaction, whereas lipin1 did not affect the function of other adipocyte-related transcription factors such as C/EBP alpha, liver X-activated receptor alpha, or sterol regulatory element binding protein 1c. In mature adipocytes, lipin1 was specifically recruited to the PPAR gamma-response elements of the phosphoenolpyruvate carboxykinase gene, an adipocyte-specific gene. C/EBP alpha up-regulates lipin1 transcription by directly binding to the lipin1 promoter. Based on the existence of a positive feedback loop between C/EBP alpha and PPAR gamma(2), we propose that lipin1 functions as an amplifier of the network between these factors, resulting in the maintenance of high levels of the specific gene expression that are required for adipogenesis and mature adipocyte functions.

[Congenital generalized lipodystrophy: a case report with neurological involvement]

Congenital generalized lipodystrophy (CGL) is a rare disorder characterized by near complete absence of adipose tissue from birth. At least 2 genes located in 9q34 (AGPAT2) and 11q13 (Seipin) are implicated in type 1 and 2, respectively, and result in insulin resistance. We report here a novel case of CGL type 1 resulting from a novel homozygote mutation in the AGPAT2 gene. The clinical picture included pseudoathletic muscular hypertrophy, hypertrophic cardiomyopathy, enlarged liver, hypermetabolism rate, and hyperinsulinemia in a 1-year-old child from Libya. Peripheral hypertonia and reflex excitability revealed signal abnormalities in white matter on magnetic resonance imagery, which has not been described previously in the literature.

Prioritization of candidate disease genes for metabolic syndrome by computational analysis of its defining phenotypes

There is a rapid increase in the world-wide burden of disease attributed to metabolic syndrome, as defined by co-occurrence of an array of phenotypes including abdominal obesity, dysglycemia, hypertriglyceridemia, low levels of high density lipoprotein cholesterol, and hypertension. Familial studies clearly indicate a genetic component to the disease and many linkage studies have identified a large number of linked loci. No disease-causing genes, however, have been conclusively identified, most likely because this is a multigenic disease for which effects of many causative genes may be small and combined with environmental effects. To assist empirical identification of metabolic syndrome associated genes, we present here a novel computational approach to prioritize candidate genes. We have used linkage studies and the clinical and population-specific presentation of the disease to select a final candidate gene list of 19 most likely disease-causing genes. These are predominantly involved in chylomicron processing, transmembrane receptor activity, and signal transduction pathways. We propose here that information about the clinical presentation of a complex trait can be used to effectively inform computational prioritization of disease-causing genes for that trait.

Efficacy and safety of pioglitazone in treatment of a patient with an atypical partial lipodystrophy syndrome

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.

Genetic forms of the cardiometabolic syndrome: what can they tell the clinician?

A well-worn medical aphorism states that "when you hear hoof beats, think of a horse and not a zebra." When applying this principle to the cardiometabolic syndrome (CMS), the horse would be represented by the prevalent CMS phenotype that affects approximately 30% of individuals in Westernized societies, while the zebra is represented by very rare conditions--such as lipodystrophy syndromes--that share some features with the more prevalent CMS. For instance, familial partial lipodystrophy types 2 and 3 result from heterozygous mutations in LMNA, encoding nuclear lamin A/C, and in PPARG, encoding peroxisome proliferator-activated receptor (PPAR)-gamma, respectively. Patients with either subtype of partial lipodystrophy exhibit an increased ratio of central to peripheral fat stores, dysglycemia, dyslipidemia, and hypertension, with predisposition for developing insulin-resistant diabetes and atherosclerosis end points. Sometimes, however, the zebra serves as a model that can help us understand the horse, so that the rare partial lipodystrophies might offer some insight into pathogenesis and treatment of the more prevalent CMS.

Mechanisms of the components of the metabolic syndrome that predispose to diabetes and atherosclerotic CVD

The metabolic syndrome represents a summation of obesity-driven risk factors for atherosclerotic CVD and type 2 diabetes. Definitions of the syndrome vary but in general agree closely in identifying subjects. The relationships between the metabolic syndrome and atherosclerotic CVD and diabetes also vary, with relative risks of approximately 1.5-3.0 and approximately 3.0-5.0 respectively. Insulin resistance appears to explain much of the pathophysiology of the syndrome. Both increased fatty acid flux and an excess of circulating pro-inflammatory cytokines are likely mediators. With increased waist circumference, increases in fatty acid delivery to the liver result in higher rates of hepatic glucose production and increases in the secretion of apoB-containing lipoproteins. Concomitant changes in HDL ensue, including a replacement of the cholesterol content with TAG, an accelerated clearance from the plasma and thus a reduced number of HDL particles. Typically also present are increases in small dense LDL. Hypertension in part relates to the insulin resistance, but may involve other mechanisms. Impaired fasting glucose often relates to defects in insulin secretion in addition to insulin resistance, and probably more than any other component of the syndrome predicts the increased incidence of type 2 diabetes. Although not included in the diagnostic criteria, increases in pro-inflammatory cytokines and pro-thrombotic factors, in addition to decreases in plasma adiponectin, may also contribute to the increased incidence of atherosclerotic CVD and diabetes. In general, the greater the number of metabolic syndrome components, the greater the risk for these outcomes. The cytokines and pro-thrombotic factors also appear to contribute.

Familial partial lipodystrophy phenotype resulting from a single-base mutation in deoxyribonucleic acid-binding domain of peroxisome proliferator-activated receptor-gamma

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.

Long-term efficacy of leptin replacement in patients with Dunnigan-type familial partial lipodystrophy

The Dunnigan-type familial partial lipodystrophy (FPLD) is characterized by a variable loss of fat from the extremities and trunk and excess subcutaneous fat in the chin and supraclavicular area. Associated metabolic abnormalities include hypoleptinemia, insulin resistance, and dyslipidemia. Our goal was to observe changes in metabolic parameters for patients with FPLD on long-term leptin replacement and to compare the metabolic characteristics seen in FPLD with those seen in generalized lipodystrophy (GL) from our previous studies. This was an open-label study of 6 patients with FPLD receiving maximal doses of oral antidiabetic and lipid-lowering medications at baseline. Recombinant leptin was given through twice-daily subcutaneous injections at a maximal dose of 0.08 mg/kg per day over 12 months to simulate normal to high normal physiologic levels. Triglycerides were reduced by 65% at 4 months (749+/-331 to 260+/-58 mg/dL) and significantly reduced at 12 months for 5 patients (433+/-125 to 247+/-69 mg/dL; P=.03). Total cholesterol also decreased (280+/-49 to 231+/-41 mg/dL; P=.01). Insulin sensitivity and fasting glucose levels (190+/-26 to 151+/-15 mg/dL; P<.01) improved. Glucose tolerance and glycosylated hemoglobin levels (8.4%+/-0.6% to 8.0%+/-0.4%; P=.07) did not change. As shown in patients with GL, patients with FPLD have improvement in triglycerides, fasting glucose, and insulin sensitivity with leptin replacement. In contrast to the patients with GL, the patients with FPLD are older, have higher leptin levels, and notably lower insulin secretion for a similar degree of hyperglycemia. Low-dose recombinant methionyl human leptin for patients with FPLD has an important role in improving triglycerides, beyond that of available lipid-lowering agents. In improving glycemic control, normalization of glucose tolerance in hypoinsulinemic patients with FPLD requires insulin and leptin therapy. This is the first study to examine the effects of long-term leptin replacement in patients with FPLD.

Thematic review series: Adipocyte Biology. Lipodystrophies: windows on adipose biology and metabolism

The lipodystrophies are characterized by loss of adipose tissue in some anatomical sites, frequently with fat accumulation in nonatrophic depots and ectopic sites such as liver and muscle. Molecularly characterized forms include Dunnigan-type familial partial lipodystrophy (FPLD), partial lipodystrophy with mandibuloacral dysplasia (MAD), Berardinelli-Seip congenital generalized lipodystrophy (CGL), and some cases with Barraquer-Simons acquired partial lipodystrophy (APL). The associated mutant gene products include 1) nuclear lamin A in FPLD type 2 and MAD type A; 2) nuclear lamin B2 in APL; 3) nuclear hormone receptor peroxisome proliferator-activated receptor gamma in FPLD type 3; 4) lipid biosynthetic enzyme 1-acylglycerol-3-phosphate O-acyltransferase 2 in CGL type 1; 5) integral endoplasmic reticulum membrane protein seipin in CGL type 2; and 6) metalloproteinase ZMPSTE24 in MAD type B. An unresolved question is whether metabolic disturbances are secondary to adipose repartitioning or result from a direct effect of the mutant gene product. Careful analysis of clinical, biochemical, and imaging phenotypes, using an approach called "phenomics," reveals differences between genetically stratified subtypes that can be used to guide basic experiments and to improve our understanding of common clinical entities, such as metabolic syndrome or the partial lipodystrophy syndrome associated with human immunodeficiency virus infection.

Peroxisomal proliferator activated receptor-gamma deficiency in a Canadian kindred with familial partial lipodystrophy type 3 (FPLD3)

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-gamma. 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-gamma 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.

The classification of diabetes mellitus: a conceptual framework

Diabetes is the extreme manifestation of a spectrum conditions in which the balance of insulin secretion and insulin action (or insulin resistance) has been altered. Loss of euglycemia is caused by relative insulin deficiency in the presence of insulin resistance, or by absolute insulin deficiency. There are related conditions in which an alteration of insulin resistance or beta-cell dysfunction exists, but because of compensation glucose homeostasis has not been lost. The elucidation of the causes of insulin resistance and -cell failure and the attention to the different degrees of insulin deficiency and insulin resistance allow for better diagnosis, treatment, and prevention of diabetes and its related conditions.

Genetic and physiological insights into the metabolic syndrome

The metabolic syndrome (MetS) is a common phenotype that is clinically defined by threshold values applied to measures of central obesity, dysglycemia, dyslipidemia, and/or elevated blood pressure, which must be present concurrently in any one of a variety of combinations. Insulin resistance, although not a defining component of the MetS, is nonetheless considered to be a core feature. MetS is important because it is rapidly growing in prevalence and is strongly related to the development of cardiovascular disease. To define etiology, pathogenesis and expression of MetS, we have studied patients, specifically Canadian families and communities. One example is familial partial lipodystrophy (FPLD), a rare monogenic form of insulin resistance caused by mutations in either LMNA, encoding nuclear lamin A/C (subtype FPLD2), or in PPARG, encoding peroxisomal proliferator-activated receptor-gamma (subtype FPLD3). Because it evolves slowly and recapitulates key clinical and biochemical attributes, FPLD seems to be a useful monogenic model of MetS. A second example is the disparate MetS prevalence between two Canadian aboriginal groups that is mirrored by disparate prevalence of diabetes and cardiovascular disease. Careful phenotypic evaluation of such special cases of human MetS by using a wide range of diagnostic methods, an approach called "phenomics," may help uncover early presymptomatic disease biomarkers, which in turn might reveal new pathways and targets for interventions for MetS, diabetes, and atherosclerosis.

Transcriptional mechanisms of hippocampal aging

Aging related cognitive decline is an increasing health problem but affects only a subset of elderly humans. This research uses outbred young (Y) and aged rats. Behavioral characterization distinguishes aged rats with impaired spatial learning (AI) and aged rats with unimpaired learning ability (AU), mimicking the varied susceptibility of the human population to age-associated learning impairment. Studies are testing a hypothesis that hippocampal transcriptional mechanisms and gene expression profiles linked to activator protein-1 (AP-1) and glucocorticoid receptor (GR), mineralocorticoid receptor (MR) or cyclic AMP response element binding protein (CREB) families of transcription factors distinguish successful or unsuccessful aging and cognition. Results from mRNA assays, in situ hybridization, electromobility shift assays and western immunoblot indicate changes in GR and CREB in AI rats. State of the art future approaches to define downstream transcription targets are described.

Altered pre-lamin A processing is a common mechanism leading to lipodystrophy

Lipodystrophies are a heterogeneous group of human disorders characterized by the anomalous distribution of body fat associated with insulin resistance and altered lipid metabolism. The pathogenetic mechanism of inherited lipodystrophies is not yet clear; at the molecular level they have been linked to mutations of lamin A/C, peroxisome proliferator-activated receptor (PPARgamma) and other seemingly unrelated proteins. In this study, we examined lamin A/C processing in three laminopathies characterized by lipodystrophic phenotypes: Dunnigan type familial partial lipodystrophy, mandibuloacral dysplasia and atypical Werner's syndrome. We found that the lamin A precursor was specifically accumulated in lipodystrophy cells. Pre-lamin A was located at the nuclear envelope and co-localized with the adipocyte transcription factor sterol regulatory element binding protein 1 (SREBP1). Using co-immunoprecipitation experiments, we obtained the first demonstration of an in vivo interaction between SREBP1 and pre-lamin A. Binding of SREBP1 to the lamin A precursor was detected in patient fibroblasts as well as in control fibroblasts forced to accumulate pre-lamin A by farnesylation inhibitors. In contrast, SREBP1 did not interact in vivo with mature lamin A or C in cultured fibroblasts. To gain insights into the effect of pre-lamin A accumulation in adipose tissue, we inhibited lamin A precursor processing in 3T3-L1 pre-adipocytes. Our results show that pre-lamin A sequesters SREBP1 at the nuclear rim, thus decreasing the pool of active SREBP1 that normally activates PPARgamma and causing impairment of pre-adipocyte differentiation. This defect can be rescued by treatment with troglitazone, a known PPARgamma ligand activating the adipogenic program.

The metabolic syndrome

The metabolic syndrome is a common metabolic disorder that results from the increasing prevalence of obesity. The disorder is defined in various ways, but in the near future a new definition(s) will be applicable worldwide. The pathophysiology seems to be largely attributable to insulin resistance with excessive flux of fatty acids implicated. A proinflammatory state probably contributes to the syndrome. The increased risk for type 2 diabetes and cardiovascular disease demands therapeutic attention for those at high risk. The fundamental approach is weight reduction and increased physical activity; however, drug treatment could be appropriate for diabetes and cardiovascular disease risk reduction.

PPARγ: A Critical Determinant of Body Fat Distribution in Humans and Mice

Evidence emerging from studies of humans and mice has indicated peroxisome proliferator-activated receptor gamma (PPARgamma) to be not only a key factor for adipogenesis but also a critical determinant of body fat distribution. Whereas genetically reduced PPARgamma activity in adipose tissue leads to reduction of total fat mass in humans and in mice, mutations in the ligand-binding domain of PPARgamma cause abnormal body fat distributions. It is less clear from mutation analysis how PPARgamma is involved in metabolic disturbances such as insulin resistance and its cardiovascular complications. Nevertheless, similarities and differences in the phenotypes associated with PPARgamma mutations in humans and in mouse models provide opportunities to dissect relationships between body fat distribution and its metabolic complications.

Laminopathies and Atherosclerosis

Laminopathies are genetic diseases that encompass a wide spectrum of phenotypes with diverse tissue pathologies and result mainly from mutations in the LMNA gene encoding nuclear lamin A/C. Some laminopathies affect the cardiovascular system, and a few (namely, Dunnigan-type familial partial lipodystrophy [FPLD2] and Hutchinson-Gilford progeria syndrome [HGPS]) feature atherosclerosis as a key component. The premature atherosclerosis of FPLD2 is probably related to characteristic proatherogenic metabolic disturbances such as dyslipidemia, hyperinsulinemia, hypertension, and diabetes. In contrast, the premature atherosclerosis of HGPS occurs with less exposure to metabolic proatherogenic traits and probably reflects the generalized process of accelerated aging in HGPS. Although some common polymorphisms of LMNA have been associated with traits related to atherosclerosis, the monogenic diseases FPLD2 and HGPS are more likely to provide clues about new pathways for the general process of atherosclerosis.