The renal manifestations of type 4 familial partial lipodystrophy: a case report and review of literature

Molecular mechanisms of perilipin protein function in lipid droplet metabolism

Perilipins are abundant lipid droplet (LD) proteins present in all metazoans and also in Amoebozoa and fungi. Humans express five perilipins, which share a similar domain organization: an amino-terminal PAT domain and an 11-mer repeat region, which can fold into amphipathic helices that interact with LDs, followed by a structured carboxy-terminal domain. Variations of this organization that arose during vertebrate evolution allow for functional specialization between perilipins in relation to the metabolic needs of different tissues. We discuss how different features of perilipins influence their interaction with LDs and their cellular targeting. PLIN1 and PLIN5 play a direct role in lipolysis by regulating the recruitment of lipases to LDs and LD interaction with mitochondria. Other perilipins, particularly PLIN2, appear to protect LDs from lipolysis, but the molecular mechanism is not clear. PLIN4 stands out with its long repetitive region, whereas PLIN3 is most widely expressed and is used as a nascent LD marker. Finally, we discuss the genetic variability in perilipins in connection with metabolic disease, prominent for PLIN1 and PLIN4, underlying the importance of understanding the molecular function of perilipins.

Lipid metabolism disorder in diabetic kidney disease

Diabetic kidney disease (DKD), a significant complication associated with diabetes mellitus, presents limited treatment options. The progression of DKD is marked by substantial lipid disturbances, including alterations in triglycerides, cholesterol, sphingolipids, phospholipids, lipid droplets, and bile acids (BAs). Altered lipid metabolism serves as a crucial pathogenic mechanism in DKD, potentially intertwined with cellular ferroptosis, lipophagy, lipid metabolism reprogramming, and immune modulation of gut microbiota (thus impacting the liver-kidney axis). The elucidation of these mechanisms opens new potential therapeutic pathways for DKD management. This research explores the link between lipid metabolism disruptions and DKD onset.

Perilipin 1: a systematic review on its functions on lipid metabolism and atherosclerosis in mice and humans

The function of perilipin 1 in human metabolism was recently highlighted by the description of PLIN1 variants associated with various pathologies. These include severe familial partial lipodystrophy and early onset acute coronary syndrome. Additionally, certain variants have been reported to have a protective effect on cardiovascular diseases. The role of this protein remains controversial in mice and variant interpretation in humans is still conflicting. This literature review has two primary objectives (i) to clarify the function of the PLIN1 gene in lipid metabolism and atherosclerosis by examining functional studies performed in cells (adipocytes) and mice and (ii) to understand the impact of PLIN1 variants identified in humans based on the variant's location within the protein and the type of variant (missense or frameshift). To achieve these objectives, we conducted an extensive analysis of the relevant literature on perilipin 1, its function in cellular models and mice, and the consequences of its mutations in humans. We also utilized bioinformatics tools and consulted the Human Genetics Cardiovascular Disease Knowledge Portal to enhance the pathogenicity assessment of PLIN1 missense variants.

Kidney lipid dysmetabolism and lipid droplet accumulation in chronic kidney disease

Chronic kidney disease (CKD) is a global health problem with rising incidence and prevalence. Among several pathogenetic mechanisms responsible for disease progression, lipid accumulation in the kidney parenchyma might drive inflammation and fibrosis, as has been described in fatty liver diseases. Lipids and their metabolites have several important structural and functional roles, as they are constituents of cell and organelle membranes, serve as signalling molecules and are used for energy production. However, although lipids can be stored in lipid droplets to maintain lipid homeostasis, lipid accumulation can become pathogenic. Understanding the mechanisms linking kidney parenchymal lipid accumulation to CKD of metabolic or non-metabolic origin is challenging, owing to the tremendous variety of lipid species and their functional diversity across different parenchymal cells. Nonetheless, multiple research reports have begun to emphasize the effect of dysregulated kidney lipid metabolism in CKD progression. For example, altered cholesterol and fatty acid metabolism contribute to glomerular and tubular cell injury. Newly developed lipid-targeting agents are being tested in clinical trials in CKD, raising expectations for further therapeutic development in this field.

Histological Manifestations of Diabetic Kidney Disease and its Relationship with Insulin Resistance

Histological manifestations of diabetic kidney disease (DKD) include mesangiolysis, mesangial matrix expansion, mesangial cell proliferation, thickening of the glomerular basement membrane, podocyte loss, foot process effacement, and hyalinosis of the glomerular arterioles, interstitial fibrosis, and tubular atrophy. Glomerulomegaly is a typical finding. Histological features of DKD may occur in the absence of clinical manifestations, having been documented in patients with normal urinary albumin excretion and normal glomerular filtration rate. Furthermore, the histological picture progresses over time, while clinical data may remain normal. Conversely, histological lesions of DKD improve with metabolic normalization following effective pancreas transplantation. Insulin resistance has been associated with the clinical manifestations of DKD (nephromegaly, glomerular hyperfiltration, albuminuria, and kidney failure). Likewise, insulin resistance may underlie the histological manifestations of DKD. Morphological changes of DKD are absent in newly diagnosed type 1 diabetes patients (with no insulin resistance) but appear afterward when insulin resistance develops. In contrast, structural lesions of DKD are typically present before the clinical diagnosis of type 2 diabetes. Several heterogeneous conditions that share the occurrence of insulin resistance, such as aging, obesity, acromegaly, lipodystrophy, cystic fibrosis, insulin receptor dysfunction, and Alström syndrome, also share both clinical and structural manifestations of kidney disease, including glomerulomegaly and other features of DKD, focal segmental glomerulosclerosis, and C3 glomerulopathy, which might be ascribed to the reduction in the synthesis of factor H binding sites (such as heparan sulfate) that leads to uncontrolled complement activation. Alström syndrome patients show systemic interstitial fibrosis markedly similar to that present in diabetes.

Hereditary severe insulin resistance syndrome: Pathogenesis, pathophysiology, and clinical management

Severe insulin resistance has been linked to some of the most globally prevalent disorders, such as diabetes mellitus, nonalcoholic fatty liver disease, polycystic ovarian syndrome, and hypertension. Hereditary severe insulin resistance syndrome (H-SIRS) is a rare disorder classified into four principal categories: primary insulin receptor defects, lipodystrophies, complex syndromes, and obesity-related H-SIRS. Genes such as INSR, AKT2, TBC1D4, AGPAT2, BSCL2, CAV1, PTRF, LMNA, PPARG, PLIN1, CIDEC, LIPE, PCYT1A, MC4R, LEP, POMC, SH2B1, RECQL2, RECQL3, ALMS1, PCNT, ZMPSTE24, PIK3R1, and POLD1 have been linked to H-SIRS. Its clinical features include insulin resistance, hyperglycemia, hyperandrogenism, severe dyslipidemia, fatty liver, abnormal topography of adipose tissue, and low serum leptin and adiponectin levels. Diagnosis of H-SIRS is based on the presence of typical clinical features associated with the various H-SIRS forms and the identification of mutations in H-SIRS-linked genes by genetic testing. Diet therapy, insulin sensitization, exogenous insulin therapy, and leptin replacement therapy have widely been adopted to manage H-SIRS. The rarity of H-SIRS, its highly variable clinical presentation, refusal to be tested for genetic mutations by patients' family members who are not severely sick, unavailability of genetic testing, and testing expenses contribute to the delayed or underdiagnoses of H-SIRS. Early diagnosis facilitates early management of the condition, which results in improved glycemic control and delayed onset of diabetes and other complications related to severe insulin resistance. The use of updated genetic sequencing technologies is recommended, and long-term studies are required for genotype-phenotype differentiation and formulation of diagnostic and treatment protocols.

Case report: Focal segmental glomerulosclerosis in a pediatric atypical progeroid syndrome

Atypical progeroid syndrome (APS) is a rare type of progeroid syndrome mainly caused by heterozygous missense mutations in the LMNA (MIM 150330) gene. APS has heterogeneous clinical manifestations, and its kidney manifestations, particularly in children, are rarely documented. Here, we report the first pediatric case of APS with focal segmental glomerulosclerosis (FSGS). A 10-year-old boy with progeroid features was referred to the nephrology clinic because of hyperuricemia. He had dark skin, protruding eyes, and beaked nose and was very thin, suggesting lipodystrophy. He had been treated for recurrent urinary tract infection during infancy, and liver biopsy for persisting hepatitis showed steatohepatitis. He also had hypertrophic cardiomyopathy (HCMP) with mitral and tricuspid valve regurgitation. Genetic studies were performed considering his multisystem symptoms, and he was diagnosed as having APS according to exome sequencing findings (c.898G > C, p.Asp300His of LMNA). During the first visit to the nephrology clinic, he had minimal proteinuria (urine protein/creatinine ratio of 0.23 mg/mg), which worsened during follow-up. In three years, his urine protein/creatinine ratio and N-acetyl-b-D-glucosaminidase/creatinine ratio increased to 1.52 and 18.7, respectively. The kidney biopsy result was consistent with findings of FSGS, peri-hilar type, showing segmental sclerosis of 1 (5%) glomerulus out of 21 glomeruli. An angiotensin receptor blocker was added to manage his proteinuria. This is the first pediatric report of FSGS in an APS patient with confirmed LMNA defect, who manifested progeroid features, lipodystrophy, HCMP with heart valve dysfunction, and steatohepatitis. Our case suggests that screening for proteinuric nephropathy is essential for managing APS patients since childhood.

Familial partial lipodystrophy syndromes

Lipodystrophies are a heterogeneous group of rare conditions characterised by the loss of adipose tissue. The most common forms are the familial partial lipodystrophy (FPLD) syndromes, which include a set of disorders, usually autosomal dominant, due to different pathogenetic mechanisms leading to improper fat distribution (loss of fat in the limbs and gluteal region and variable regional fat accumulation). Affected patients are prone to suffering serious morbidity via the development of metabolic complications associated to insulin resistance and an inability to properly store lipids. Although no well-defined diagnostic criteria have been established for lipodystrophy, there are certain clues related to medical history, physical examination and body composition evaluation that may suggest FPLD prior to confirmatory genetic analysis. Its treatment must be fundamentally oriented towards the control of the metabolic abnormalities. In this sense, metreleptin therapy, the newer classes of hypoglycaemic agents and other investigational drugs are showing promising results. This review aims to summarise the current knowledge of FPLD syndromes and to describe their clinical and molecular picture, diagnostic approaches and recent treatment modalities.

Severe insulin resistance syndromes

Severe insulin resistance syndromes are a heterogeneous group of rare disorders characterized by profound insulin resistance, substantial metabolic abnormalities, and a variety of clinical manifestations and complications. The etiology of these syndromes may be hereditary or acquired, due to defects in insulin potency and action, cellular responsiveness to insulin, and/or aberrations in adipose tissue function or development. Over the past decades, advances in medical technology, particularly in genomic technologies and genetic analyses, have provided insights into the underlying pathophysiological pathways and facilitated the more precise identification of several of these conditions. However, the exact cellular and molecular mechanisms of insulin resistance have not yet been fully elucidated for all syndromes. Moreover, in clinical practice, many of the syndromes are often misdiagnosed or underdiagnosed. The majority of these disorders associate with an increased risk of severe complications and mortality; thus, early identification and personalized clinical management are of the essence. This Review aims to categorize severe insulin resistance syndromes by disease process, including insulin receptor defects, signaling defects, and lipodystrophies. We also highlight several complex syndromes and emphasize the need to identify patients, investigate underlying disease mechanisms, and develop specific treatment regimens.

New insights into renal lipid dysmetabolism in diabetic kidney disease

Lipid dysmetabolism is one of the main features of diabetes mellitus and manifests by dyslipidemia as well as the ectopic accumulation of lipids in various tissues and organs, including the kidney. Research suggests that impaired cholesterol metabolism, increased lipid uptake or synthesis, increased fatty acid oxidation, lipid droplet accumulation and an imbalance in biologically active sphingolipids (such as ceramide, ceramide-1-phosphate and sphingosine-1-phosphate) contribute to the development of diabetic kidney disease (DKD). Currently, the literature suggests that both quality and quantity of lipids are associated with DKD and contribute to increased reactive oxygen species production, oxidative stress, inflammation, or cell death. Therefore, control of renal lipid dysmetabolism is a very important therapeutic goal, which needs to be archived. This article will review some of the recent advances leading to a better understanding of the mechanisms of dyslipidemia and the role of particular lipids and sphingolipids in DKD.

Role of TGF-β signalling in PCOS associated focal segmental glomerulosclerosis

Research on polycystic ovarian syndrome (PCOS) remains intense due to its evolving impact on metabolism, reproduction and cardiovascular function. Changes in metabolic pathways can also significantly impact renal function including the development of Focal Segmental Glomerulosclerosis (FSGS), one of the most highly investigated renal diseases. In FSGS, scarring of the glomerulus vascular tuft damages the kidneys. Onset of FSGS may either be congenital or due to other disorders that affect the metabolism and normal kidney function. Both PCOS and FSGS appear to be associated with Transforming Growth Factor-β (TGF-β) signalling. Over-expression of TGF-β may be due to the activation of the thrombospondin 1 (TSP1) gene, which increases the probability of developing renal disorders. Higher androgen levels in PCOS may also cause podocyte damage thus directly impacting development of FSGS. This article reviews the role of TGF-β's in PCOS and FSGS and explores the inter-relationship between these two disorders.

Diagnostic strategies and clinical management of lipodystrophy

Introduction: Lipodystrophy is a heterogeneous group of rare diseases characterized by various degrees of fat loss which leads to serious morbidity due to metabolic abnormalities associated with insulin resistance and subtype-specific clinical features associated with underlying molecular etiology.Areas covered: This article aims to help physicians address challenges in diagnosing and managing lipodystrophy. We systematically reviewed the literature on PubMed and Google Scholar databases to summarize the current knowledge in lipodystrophy management.Expert opinion: Adipose tissue is a highly active endocrine organ that regulates metabolic homeostasis in the human body through a comprehensive communication network with other organ systems such as the central nervous system, liver, digestive system, and the immune system. The adipose tissue is capable of producing and secreting numerous factors with important endocrine functions such as leptin that regulates energy homeostasis. Recent developments in the field have helped to solve some of the mysteries behind lipodystrophy that allowed us to get a better understanding of adipocyte function and differentiation. From a clinical standpoint, physicians who suspect lipodystrophy should distinguish the disease from several others that may present with similar clinical features. It is also important for physicians to carefully interpret clinical features, laboratory, and imaging results before moving to more sophisticated tests and making decisions about therapy.

Diagnostic Challenge in PLIN1-Associated Familial Partial Lipodystrophy

CONTEXT

Heterozygous frameshift variants in PLIN1 encoding perilipin-1, a key protein for lipid droplet formation and triglyceride metabolism, have been implicated in familial partial lipodystrophy type 4 (FPLD4), a rare entity with only six families reported worldwide. The pathogenicity of other PLIN1 null variants identified in patients with diabetes and/or hyperinsulinemia was recently questioned because of the absence of lipodystrophy in these individuals and the elevated frequency of PLIN1 null variants in the general population.

OBJECTIVES

To reevaluate the pathogenicity of PLIN1 frameshift variants owing to new data obtained in the largest series of patients with FPLD4.

METHODS

We performed histological and molecular studies for patients referred to our French National Reference Center for Rare Diseases of Insulin Secretion and Insulin Sensitivity for lipodystrophy and/or insulin resistance and carrying PLIN1 frameshift variants.

RESULTS

We identified two heterozygous PLIN1 frameshift variants segregating with the phenotype in nine patients from four unrelated families. The FPLD4 stereotypical signs included postpubertal partial lipoatrophy of variable severity, muscular hypertrophy, acromegaloid features, polycystic ovary syndrome and/or hirsutism, metabolic complications (e.g., hypertriglyceridemia, liver steatosis, insulin resistance, diabetes), and disorganized subcutaneous fat lobules with fibrosis and macrophage infiltration.

CONCLUSIONS

These data suggest that some FPLD4-associated PLIN1 variants are deleterious. Thus, the evidence for the pathogenicity of each variant ought to be carefully considered before genetic counseling, especially given the importance of an early diagnosis for optimal disease management. Thus, we recommend detailed familial investigation, adipose tissue-focused examination, and follow-up of metabolic evolution.