HIV-protease inhibitors block the enzymatic activity of purified Ste24p

We reported that several HIV protease inhibitors (HIV-PIs) interfere with the endoproteolytic processing of two farnesylated proteins, yeast a-factor and mammalian prelamin A. We proposed that these drugs interfere with prelamin A processing by blocking ZMPSTE24, an integral membrane zinc metalloproteinase known to play a critical role in its processing. However, because all of the drug inhibition studies were performed with cultured fibroblasts or crude membrane fractions rather than on purified enzyme preparations, no definitive conclusions could be drawn. Here, we purified Ste24p, the yeast ortholog of ZMPSTE24, and showed that its enzymatic activity was blocked by three HIV-PIs (lopinavir, ritonavir, and tipranavir). A newer HIV-PI, darunavir, had little effect on Ste24p activity. None of the HIV-PIs had dramatic effects on the enzymatic activity of purified Ste14p, the prenylprotein methyltransferase. These studies strongly support our hypothesis that HIV-PIs block prelamin A processing by directly affecting the enzymatic activity of ZMPSTE24, and in this way they may contribute to lipodystrophy in individuals undergoing HIV-PI treatment.     

Inhibitors of protein geranylgeranyltransferase-I lead to prelamin A accumulation in cells by inhibiting ZMPSTE24

Protein farnesyltransferase (FTase) inhibitors, generally called "FTIs," block the farnesylation of prelamin A, inhibiting the biogenesis of mature lamin A and leading to an accumulation of prelamin A within cells. A recent report found that a GGTI, an inhibitor of protein geranylgeranyltransferase-I (GGTase-I), caused an exaggerated accumulation of prelamin A in the presence of low amounts of an FTI. This finding was interpreted as indicating that prelamin A can be alternately prenylated by GGTase-I and that inhibiting both protein prenyltransferases leads to more prelamin A accumulation than blocking FTase alone. Here, we tested an alternative hypothesis-GGTIs are not specific for GGTase-I, and they lead to prelamin A accumulation by inhibiting ZMPSTE24 (a zinc metalloprotease that converts farnesyl-prelamin A to mature lamin A). In our studies, commonly used GGTIs caused prelamin A accumulation in human fibroblasts, but the prelamin A in GGTI-treated cells exhibited a more rapid electrophoretic mobility than prelamin A from FTI-treated cells. The latter finding suggested that the prelamin A in GGTI-treated cells might be farnesylated (which would be consistent with the notion that GGTIs inhibit ZMPSTE24). Indeed, metabolic labeling studies revealed that the prelamin A in GGTI-treated fibroblasts is farnesylated. Moreover, biochemical assays of ZMPSTE24 activity showed that ZMPSTE24 is potently inhibited by a GGTI. Our studies show that GGTIs inhibit ZMPSTE24, leading to an accumulation of farnesyl-prelamin A. Thus, caution is required when interpreting the effects of GGTIs on prelamin A processing.     

Autophagic degradation of farnesylated prelamin A as a therapeutic approach to lamin-linked progeria

Farnesylated prelamin A is a processing intermediate produced in the lamin A maturation pathway. Accumulation of a truncated farnesylated prelamin A form, called progerin, is a hallmark of the severe premature ageing syndrome, Hutchinson-Gilford progeria. Progerin elicits toxic effects in cells, leading to chromatin damage and cellular senescence and ultimately causes skin and endothelial defects, bone resorption, lipodystrophy and accelerated ageing. Knowledge of the mechanism underlying prelamin A turnover is critical for the development of clinically effective protein inhibitors that can avoid accumulation to toxic levels without impairing lamin A/C expression, which is essential for normal biological functions. Little is known about specific molecules that may target farnesylated prelamin A to elicit protein degradation. Here, we report the discovery of rapamycin as a novel inhibitor of progerin, which dramatically and selectively decreases protein levels through a mechanism involving autophagic degradation. Rapamycin treatment of progeria cells lowers progerin, as well as wild-type prelamin A levels, and rescues the chromatin phenotype of cultured fibroblasts, including histone methylation status and BAF and LAP2alpha distribution patterns. Importantly, rapamycin treatment does not affect lamin C protein levels, but increases the relative expression of the prelamin A endoprotease ZMPSTE24. Thus, rapamycin, an antibiotic belonging to the class of macrolides, previously found to increase longevity in mouse models, can serve as a therapeutic tool, to eliminate progerin, avoid farnesylated prelamin A accumulation, and restore chromatin dynamics in progeroid laminopathies.     

核层蛋白A前体的法尼基化与衰老

编码核层蛋白A(lamin A)的LMNA基因突变导致法尼基化的核层蛋白A前体(prelamin A)不能被进一步加工成成熟的核层蛋白A,从而导致一种Hutchinson-Gilford早老症综合征(Hutchinson-Gilford progeria syndrome,HGPS)。一种更严重的早老症——限制性皮肤病(restrictive dermopathy,RD),是由于缺失核层蛋白A前体加工过程中的剪切酶ZMPSTE24引起的。ZMPSTE24的缺失阻止了法尼基化的核层蛋白A前体不能正常加工成为成熟的核层蛋白A,同时导致法尼基化的核层蛋白A前体的堆积。在HGPS和RD病人的成纤维细胞中,发现法尼基化的核层蛋白A前体都定位在核膜,从而影响细胞核膜的完整性,并导致细胞核形的异常,进而导致衰老。最近研究表明经过法尼基酰转移酶抑制剂(farnesyltransferase inhibitor,FTI)处理后的细胞的核形异常减少。同时,FTI能够改善HGPS和RD小鼠的早老症状。本文就核层蛋白A前体的法尼基化对衰老的影响有关研究进展作一综述。     

Requirements for efficient proteolytic cleavage of prelamin A by ZMPSTE24

Background

The proteolytic maturation of the nuclear protein lamin A by the zinc metalloprotease ZMPSTE24 is critical for human health. The lamin A precursor, prelamin A, undergoes a multi-step maturation process that includes CAAX processing (farnesylation, proteolysis and carboxylmethylation of the C-terminal CAAX motif), followed by ZMPSTE24-mediated cleavage of the last 15 amino acids, including the modified C-terminus. Failure to cleave the prelamin A “tail”, due to mutations in either prelamin A or ZMPSTE24, results in a permanently prenylated form of prelamin A that underlies the premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS) and related progeroid disorders.

Methodology/Principal Findings

Here we have investigated the features of the prelamin A substrate that are required for efficient cleavage by ZMPSTE24. We find that the C-terminal 41 amino acids of prelamin A contain sufficient context to allow cleavage of the tail by ZMPSTE24. We have identified several mutations in amino acids immediately surrounding the cleavage site (between Y646 and L647) that interfere with efficient cleavage of the prelamin A tail; these mutations include R644C, L648A and N650A, in addition to the previously reported L647R. Our data suggests that 9 of the 15 residues within the cleaved tail that lie immediately upstream of the CAAX motif are not critical for ZMPSTE24-mediated cleavage, as they can be replaced by the 9 amino acid HA epitope. However, duplication of the same 9 amino acids (to increase the distance between the prenyl group and the cleavage site) impairs the ability of ZMPSTE24 to cleave prelamin A.

Conclusions/Significance

Our data reveals amino acid preferences flanking the ZMPSTE24 cleavage site of prelamin A and suggests that spacing from the farnesyl-cysteine to the cleavage site is important for optimal ZMPSTE24 cleavage. These studies begin to elucidate the substrate requirements of an enzyme activity critical to human health and longevity.     

Prelamin A farnesylation and progeroid syndromes

Hutchinson-Gilford progeria syndrome (HGPS) is caused by a LMNA mutation that leads to the synthesis of a mutant prelamin A that is farnesylated but cannot be further processed to mature lamin A. A more severe progeroid disorder, restrictive dermopathy (RD), is caused by the loss of the prelamin A-processing enzyme, ZMPSTE24. The absence of ZMPSTE24 prevents the endoproteolytic processing of farnesyl-prelamin A to mature lamin A and leads to the accumulation of farnesyl-prelamin A. In both HGPS and RD, the farnesyl-prelamin A is targeted to the nuclear envelope, where it interferes with the integrity of the nuclear envelope and causes misshapen cell nuclei. Recent studies have shown that the frequency of misshapen nuclei can be reduced by treating cells with a farnesyltransferase inhibitor (FTI). Also, administering an FTI to mouse models of HGPS and RD ameliorates the phenotypes of progeria. These studies have prompted interest in testing the efficacy of FTIs in children with HGPS.     

Targeting RAS‐converting enzyme 1 overcomes senescence and improves progeria‐like phenotypes of ZMPSTE24 deficiency

Several progeroid disorders are caused by deficiency in the endoprotease ZMPSTE24 which leads to accumulation of prelamin A at the nuclear envelope. ZMPSTE24 cleaves prelamin A twice: at the third carboxyl‐terminal amino acid following farnesylation of a –CSIM motif; and 15 residues upstream to produce mature lamin A. The carboxyl‐terminal cleavage can also be performed by RAS‐converting enzyme 1 (RCE1) but little is known about the importance of this cleavage for the ability of prelamin A to cause disease. Here, we found that knockout of RCE1 delayed senescence and increased proliferation of ZMPSTE24‐deficient fibroblasts from a patient with non‐classical Hutchinson‐Gilford progeria syndrome (HGPS), but did not influence proliferation of classical LMNA‐mutant HGPS cells. Knockout of Rce1 in Zmpste24‐deficient mice at postnatal week 4–5 increased body weight and doubled the median survival time. The absence of Rce1 in Zmpste24‐deficient fibroblasts did not influence nuclear shape but reduced an interaction between prelamin A and AKT which activated AKT‐mTOR signaling and was required for the increased proliferation. Prelamin A levels increased in Rce1‐deficient cells due to a slower turnover rate but its localization at the nuclear rim was unaffected. These results strengthen the idea that the presence of misshapen nuclei does not prevent phenotype improvement and suggest that targeting RCE1 might be useful for treating the rare progeroid disorders associated with ZMPSTE24 deficiency.     

Combined treatment with statins and aminobisphosphonates extends longevity in a mouse model of human premature aging

Several human progerias, including Hutchinson-Gilford progeria syndrome (HGPS), are caused by the accumulation at the nuclear envelope of farnesylated forms of truncated prelamin A, a protein that is also altered during normal aging. Previous studies in cells from individuals with HGPS have shown that farnesyltransferase inhibitors (FTIs) improve nuclear abnormalities associated with prelamin A accumulation, suggesting that these compounds could represent a therapeutic approach for this devastating progeroid syndrome. We show herein that both prelamin A and its truncated form progerin/LADelta50 undergo alternative prenylation by geranylgeranyltransferase in the setting of farnesyltransferase inhibition, which could explain the low efficiency of FTIs in ameliorating the phenotypes of progeroid mouse models. We also show that a combination of statins and aminobisphosphonates efficiently inhibits both farnesylation and geranylgeranylation of progerin and prelamin A and markedly improves the aging-like phenotypes of mice deficient in the metalloproteinase Zmpste24, including growth retardation, loss of weight, lipodystrophy, hair loss and bone defects. Likewise, the longevity of these mice is substantially extended. These findings open a new therapeutic approach for human progeroid syndromes associated with nuclear-envelope abnormalities.     

Accelerated ageing: from mechanism to therapy through animal models

Ageing research benefits from the study of accelerated ageing syndromes such as Hutchinson-Gilford progeria syndrome (HGPS), characterized by the early appearance of symptoms normally associated with advanced age. Most HGPS cases are caused by a mutation in the gene LMNA, which leads to the synthesis of a truncated precursor of lamin A known as progerin that lacks the target sequence for the metallopotease FACE-1/ZMPSTE24 and remains constitutively farnesylated. The use of Face-1/Zmpste24-deficient mice allowed us to demonstrate that accumulation of farnesylated prelamin A causes severe abnormalities of the nuclear envelope, hyper-activation of p53 signalling, cellular senescence, stem cell dysfunction and the development of a progeroid phenotype. The reduction of prenylated prelamin A levels in genetically modified mice leads to a complete reversal of the progeroid phenotype, suggesting that inhibition of protein farnesylation could represent a therapeutic option for the treatment of progeria. However, we found that both prelamin A and its truncated form progerin can undergo either farnesylation or geranylgeranylation, revealing the need of targeting both activities for an efficient treatment of HGPS. Using Face-1/Zmpste24-deficient mice as model, we found that a combination of statins and aminobisphosphonates inhibits both types of modifications of prelamin A and progerin, improves the ageing-like symptoms of these mice and extends substantially their longevity, opening a new therapeutic possibility for human progeroid syndromes associated with nuclear-envelope defects. We discuss here the use of this and other animal models to investigate the molecular mechanisms underlying accelerated ageing and to test strategies for its treatment.     

Human CaaX protease ZMPSTE24 expressed in yeast: Structure and inhibition by HIV protease inhibitors

The function and localization of proteins and peptides containing C‐terminal “CaaX” (Cys‐aliphatic‐aliphatic‐anything) sequence motifs are modulated by post‐translational attachment of isoprenyl groups to the cysteine sulfhydryl, followed by proteolytic cleavage of the aaX amino acids. The zinc metalloprotease ZMPSTE24 is one of two enzymes known to catalyze this cleavage. The only identified target of mammalian ZMPSTE24 is prelamin A, the precursor to the nuclear scaffold protein lamin A. ZMPSTE24 also cleaves prelamin A at a second site 15 residues upstream from the CaaX site. Mutations in ZMPSTE24 result in premature‐aging diseases and inhibition of ZMPSTE24 activity has been reported to be an off‐target effect of HIV protease inhibitors. We report here the expression (in yeast), purification, and crystallization of human ZMPSTE24 allowing determination of the structure to 2.0 Å resolution. Compared to previous lower resolution structures, the enhanced resolution provides: (1) a detailed view of the active site of ZMPSTE24, including water coordinating the catalytic zinc; (2) enhanced visualization of fenestrations providing access from the exterior to the interior cavity of the protein; (3) a view of the C‐terminus extending away from the main body of the protein; (4) localization of ordered lipid and detergent molecules at internal and external surfaces and also projecting through fenestrations; (5) identification of water molecules associated with the surface of the internal cavity. We also used a fluorogenic assay of the activity of purified ZMPSTE24 to demonstrate that HIV protease inhibitors directly inhibit the human enzyme in a manner indicative of a competitive mechanism.     

Molecular tools that block maturation of the nuclear lamin A and decelerate cancer cell migration

Lamin A contributes to the structure of nuclei in all mammalian cells and plays an important role in cell division and migration. Mature lamin A is derived from a farnesylated precursor protein, known as prelamin A, which undergoes post-translational cleavage catalyzed by the zinc metalloprotease STE24 (ZPMSTE24). Accumulation of farnesylated prelamin A in the nuclear envelope compromises cell division, impairs mitosis and induces an increased expression of inflammatory gene products. ZMPSTE24 has been proposed as a potential therapeutic target in oncology. A library of peptidomimetic compounds were synthesized and screened for their ability to induce accumulation of prelamin A in cancer cells and block cell migration in pancreatic ductal adenocarcinoma cells. The results of this study suggest that inhibitors of lamin A maturation may interfere with cell migration, the biological process required for cancer metastasis.     

HIV-protease inhibitors suppress skeletal muscle fatty acid oxidation by reducing CD36 and CPT1 fatty acid transporters

Infection with human immunodeficiency virus (HIV) and treatment with HIV-protease inhibitor (PI)-based highly active antiretroviral therapies (HAART) is associated with dysregulated fatty acid and lipid metabolism. Enhanced lipolysis, increased circulating fatty acid levels, and hepatic and intramuscular lipid accumulation appear to contribute to insulin resistance in HIV-infected people treated with PI-based HAART. However, it is unclear whether currently prescribed HIV-PIs directly alter skeletal muscle fatty acid transport, oxidation, and storage. We find that ritonavir (r, 5 µmol/l) plus 20 µmol/l of atazanavir (ATV), lopinavir (LPV), or darunavir (DRV) reduce palmitate oxidation(16–21%) in differentiated C2C12 myotubes. Palmitate oxidation was increased following exposure to high fatty acid media but this effect was blunted when myotubes were pre-exposed to the HIV-PIs. However, LPV/r and DRV/r, but not ATV/r suppressed palmitate uptake into myotubes. We found no effect of the HIV-PIs on FATP1, FATP4, or FABPpm but both CD36/FAT and carnitine palmitoyltransferase 1 (CPT1) were reduced by all three regimens though ATV/r caused only a small decrease in CPT1, relative to LPV/r or DRV/r. In contrast, sterol regulatory element binding protein-1 was increased by all 3 HIV-PIs. These findings suggest that HIV-PIs suppress fatty acid oxidation in murine skeletal muscle cells and that this may be related to decreases in cytosolic- and mitochondrial-associated fatty acid transporters. HIV-PIs may also directly impair fatty acid handling and partitioning in skeletal muscle, and this may contribute to the cluster of metabolic complications that occur in people living with HIV.     

Mislocalization of prelamin A Tyr646Phe mutant to the nuclear pore complex in human embryonic kidney 293 cells

Mature lamin A is formed after post-translational processing of prelamin A, which includes prenylation and carboxymethylation of cysteine 661 in the CaaX motif, followed by two proteolytic cleavages by zinc metalloprotease (ZMPSTE24). We expressed several prelamin A mutants, C661S (defective in prenylation), Y646F (designed to undergo prenylation but not second proteolytic cleavage), double mutant, Y646F/C661S and Y646X (mature lamin A), and the wild-type construct in human embryonic kidney (HEK-293) cells. Only the Y646F mutant co-localized with nuclear pore complex proteins, including Nup53 and Nup98, whereas the other mutants localized to the nuclear envelope rim. The cells expressing Y646F mutant also revealed abnormal nuclear morphology which was partially rescued with the farnesyl transferase inhibitors. These data suggest that the unprenylated prelamin A is not toxic to the cells. The toxicity of prenylated prelamin A may be due to its association and/or accumulation at the nuclear pore complex which could be partially reversed by farnesyl transferase inhibitors.     

Prelamin A, Zmpste24, misshapen cell nuclei, and progeria--new evidence suggesting that protein farnesylation could be important for disease pathogenesis

Prelamin A undergoes multistep processing to yield lamin A, a structural protein of the nuclear lamina. Prelamin A terminates with a CAAX motif, which triggers farnesylation of a C-terminal cysteine (the C of the CAAX motif), endoproteolytic release of the last three amino acids (the AAX), and methylation of the newly exposed farnesylcysteine residue. In addition, prelamin A is cleaved a second time, releasing 15 more residues from the C terminus (including the farnesylcysteine methyl ester), generating mature lamin A. This second cleavage step is carried out by an endoplasmic reticulum membrane protease, ZMPSTE24. Interest in the posttranslational processing of prelamin A has increased with the recognition that certain progeroid syndromes can be caused by mutations that lead to an accumulation of farnesyl-prelamin A. Recently, we showed that a key cellular phenotype of these progeroid disorders, misshapen cell nuclei, can be ameliorated by inhibitors of protein farnesylation, suggesting a potential strategy for treating these diseases. In this article, we review the posttranslational processing of prelamin A, describe several mouse models for progeroid syndromes, explain the mutations underlying several human progeroid syndromes, and summarize recent data showing that misshapen nuclei can be ameliorated by treating cells with protein farnesyltransferase inhibitors.     

Glucotoxic and diabetic conditions induce caspase 6-mediated degradation of nuclear lamin A in human islets,rodent islets and INS-1 832/13 cells

Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nuclear metabolic events, including DNA replication and organization of chromatin. The current study is aimed at understanding the role of executioner caspase 6 on lamin A integrity in islet β-cells under duress of glucotoxic (20 mM glucose; 24 h) and diabetic conditions. Under glucotoxic conditions, glucose-stimulated insulin secretion and metabolic cell viability were significantly attenuated in INS-1 832/13 cells. Further, exposure of normal human islets, rat islets and INS-1 832/13 cells to glucotoxic conditions leads to caspase 6 activation and lamin A degradation, which is also observed in islets from the Zucker diabetic fatty rat, a model for type 2 diabetes (T2D), and in islets from a human donor with T2D. Z-Val-Glu-Ile-Asp-fluoromethylketone, a specific inhibitor of caspase 6, markedly attenuated high glucose-induced caspase 6 activation and lamin A degradation, confirming that caspase 6 mediates lamin A degradation under high glucose exposure conditions. Moreover, Z-Asp-Glu-Val-Asp-fluoromethylketone, a known caspase 3 inhibitor, significantly inhibited high glucose-induced caspase 6 activation and lamin A degradation, suggesting that activation of caspase 3 might be upstream to caspase 6 activation in the islet β-cell under glucotoxic conditions. Lastly, we report expression of ZMPSTE24, a zinc metallopeptidase involved in the processing of prelamin A to mature lamin A, in INS-1 832/13 cells and human islets; was unaffected by high glucose. We conclude that caspases 3 and 6 could contribute to alterations in the integrity of nuclear lamins leading to metabolic dysregulation and failure of the islet β-cell.     

Proteomic profiling of adipose tissue from Zmpste24-/- mice, a model of lipodystrophy and premature aging, reveals major changes in mitochondrial function and vimentin processing

Lipodystrophy is a major disease involving severe alterations of adipose tissue distribution and metabolism. Mutations in genes encoding the nuclear envelope protein lamin A or its processing enzyme, the metalloproteinase Zmpste24, cause diverse human progeroid syndromes that are commonly characterized by a selective loss of adipose tissue. Similarly to humans, mice deficient in Zmpste24 accumulate prelamin A and display phenotypic features of accelerated aging, including lipodystrophy. Herein, we report the proteome and phosphoproteome of adipose tissue as well as serum metabolome in lipodystrophy by using Zmpste24(-/-) mice as experimental model. We show that Zmpste24 deficiency enhanced lipolysis, fatty acid biogenesis and β-oxidation as well as decreased fatty acid re-esterification, thus pointing to an increased partitioning of fatty acid toward β-oxidation and away from storage that likely underlies the observed size reduction of Zmpste24-null adipocytes. Besides the mitochondrial proteins related to lipid metabolism, other protein networks related to mitochondrial function, including those involved in tricarboxylic acid cycle and oxidative phosphorylation, were up-regulated in Zmpste24(-/-) mice. These results, together with the observation of an increased mitochondrial response to oxidative stress, support the relationship between defective prelamin A processing and mitochondrial dysfunction and highlight the relevance of oxidative damage in lipoatrophy and aging. We also show that absence of Zmpste24 profoundly alters the processing of the cytoskeletal protein vimentin and identify a novel protein dysregulated in lipodystrophy, High-Mobility Group Box-1 Protein. Finally, we found several lipid derivates with important roles in energy balance, such as Lysophosphatidylcholine or 2-arachidonoylglycerol, to be dysregulated in Zmpste24(-/-) serum. Together, our findings in Zmpste24(-/-) mice may be useful to unveil the mechanisms underlying adipose tissue dysfunction and its overall contribution to body homeostasis in progeria and other lipodystrophy syndromes as well as to develop novel strategies to prevent or ameliorate these diseases.     

Lamin A precursor induces barrier-to-autointegration factor nuclear localization

Lamin A, a protein component of the nuclear lamina, is synthesized as a precursor named prelamin A, whose multi-step maturation process involves different protein intermediates. As demonstrated in laminopathies such as familial partial lipodystrophy, mandibuloacral dysplasia, Werner syndrome, Hutchinson-Gilford progeria syndrome and restrictive dermopathy, failure of prelamin A processing results in the accumulation of lamin A protein precursors inside the nucleus which dominantly produces aberrant chromatin structure. To understand if nuclear lamina components may be involved in prelamin A chromatin remodeling effects, we investigated barrier-to-autointegration factor (BAF) localization and expression in prelamin A accumulating cells. BAF is a DNA-binding protein that interacts directly with histones, lamins and LEM-domain proteins and has roles in chromatin structure, mitosis and gene regulation.In this study, we show that the BAF heterogeneous localization between nucleus and cytoplasm observed in HEK293 cycling cells changes in response to prelamin A accumulation. In particular, we observed that the accumulation of lamin A, non-farnesylated prelamin A and farnesylated carboxymethylated lamin A precursors induce BAF nuclear translocation. Moreover, we show that the treatment of human fibroblasts with prelamin A interfering drugs results in similar changes. Finally, we report that the accumulation of progerin, a truncated form of farnesylated and carboxymethylated prelamin A identified in Hutchinson-Gilford progeria syndrome cells, induces BAF recruitment in the nucleus. These findings are supported by coimmunoprecipitation of prelamin A or progerin with BAF in vivo and suggest that BAF could mediate prelamin A-induced chromatin effects.     

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.