Unmasking crucial residues in adipose triglyceride lipase for coactivation with comparative gene identification-58.

Lipolysis is an essential metabolic process that releases unesterified fatty acids from neutral lipid stores to maintain energy homeostasis in living organisms. Adipose triglyceride lipase (ATGL) plays a key role in intracellular lipolysis and can be coactivated upon interaction with the protein comparative gene identification-58 (CGI-58). The underlying molecular mechanism of ATGL stimulation by CGI-58 is incompletely understood. Based on analysis of evolutionary conservation, we used site directed mutagenesis to study a C-terminally truncated variant and full-length mouse ATGL providing insights in the protein coactivation on a per-residue level. We identified the region from residues N209-N215 in ATGL as essential for coactivation by CGI-58. ATGL variants with amino acids exchanges in this region were still able to hydrolyze triacylglycerol at the basal level and to interact with CGI-58, yet could not be activated by CGI-58. Our studies also demonstrate that full-length mouse ATGL showed higher tolerance to specific single amino acid exchanges in the N209-N215 region upon CGI-58 coactivation compared to C-terminally truncated ATGL variants. The region is either directly involved in protein-protein interaction or essential for conformational changes required in the coactivation process. Three-dimensional models of the ATGL/CGI-58 complex with the artificial intelligence software AlphaFold demonstrated that a large surface area is involved in the protein-protein interaction. Mapping important amino acids for coactivation of both proteins, ATGL and CGI-58, onto the 3D model of the complex locates these essential amino acids at the predicted ATGL/CGI-58 interface thus strongly corroborating the significance of these residues in CGI-58-mediated coactivation of ATGL.

Ablation of pigment epithelium-derived factor receptor (PEDF-R/Pnpla2) causes photoreceptor degeneration.

Photoreceptor cells express the patatin-like phospholipase domain-containing 2 (PNPLA2) gene that codes for pigment epithelium-derived factor receptor (PEDF-R) (also known as ATGL). PEDF-R exhibits phospholipase activity that mediates the neurotrophic action of its ligand PEDF. Because phospholipids are the most abundant lipid class in the retina, we investigated the role of PEDF-R in photoreceptors by generating CRISPR Pnpla2 knock-out mouse lines in a retinal degeneration-free background. Pnpla2-/- mice had undetectable retinal Pnpla2 gene expression and PEDF-R protein levels as assayed by RT-PCR and immunofluorescence, respectively. The photoreceptors of mice deficient in PEDF-R had deformities as examined by histology and transmission electron microscopy. Pnpla2 knockdown diminished the PLA2 enzymatic activity of PEDF-R in the retina. Lipidomic analyses revealed the accumulation of lysophosphatidyl choline-DHA and lysophosphatidyl ethanolamine-DHA in PEDF-R-deficient retinas, suggesting a possible causal link to photoreceptor dysfunction. Loss of PEDF-R decreased levels of rhodopsin, opsin, PKCα, and synaptophysin relative to controls. Pnpla2-/- photoreceptors had surface-exposed phosphatidylserine, and their nuclei were TUNEL positive and condensed, revealing an apoptotic onset. Paralleling its structural defects, PEDF-R deficiency compromised photoreceptor function in vivo as indicated by the attenuation of photoreceptor a- and b-waves in Pnpla2-/- and Pnpla2+/- mice relative to controls as determined by electroretinography. In conclusion, ablation of PEDF-R in mice caused alteration in phospholipid composition associated with malformation and malperformance of photoreceptors. These findings identify PEDF-R as an important component for photoreceptor structure and function, highlighting its role in phospholipid metabolism for retinal survival and its consequences.

Neutral lipid storage disease with myopathy and myotonia associated to pathogenic variants on PNPLA2 and CLCN1 genes: case report.

BACKGROUND: Neutral lipid storage disease with myopathy (NLSD-M) is an autosomal recessive disease that manifests itself around the 3rd to 4th decade with chronic myopathy predominantly proximal in the shoulder girdle. Clinical myotonia is uncommon. We will report a rare case of association of pathogenic variants on PNPLA2 and CLCN1 genes with a mixed phenotype of NLSD-M and a subclinical form of Thomsen's congenital myotonia. CASE PRESENTATION: We describe a patient with chronic proximal myopathy, subtle clinical myotonia and electrical myotonia on electromyography (EMG). Serum laboratory analysis disclosure hyperCKemia (CK 1280 mg/dL). A blood smear analysis showed Jordan's anomaly, a hallmark of NLSD-M. A genetic panel was collected using next-generation sequencing (NGS) technique, which identified two pathogenic variants on genes supporting two different diagnosis: NLSD-M and Thomsen congenital myotonia, whose association has not been previously described. CONCLUSIONS: Although uncommon, it is important to remember the possibility of association of pathogenic variants to explain a specific neuromuscular disease phenotype. The use of a range of complementary methods, including myopathy genetic panels, may be essential to diagnostic definition in such cases.

Optimized expression and purification of adipose triglyceride lipase improved hydrolytic and transacylation activities in vitro.

Adipose triglyceride lipase (ATGL) plays a key role in intracellular lipolysis, the mobilization of stored triacylglycerol. This work provides an important basis for generating reproducible and detailed data on the hydrolytic and transacylation activities of ATGL. We generated full-length and C-terminally truncated ATGL variants fused with various affinity tags and analyzed their expression in different hosts, namely E.coli, the insect cell line Sf9, and the mammalian cell line human embryonic kidney 293T. Based on this screen, we expressed a fusion protein of ATGL covering residues M1-D288 flanked with N-terminal and C-terminal purification tags. Using these fusions, we identified key steps in expression and purification protocols, including production in the E. coli strain ArcticExpress (DE3) and removal of copurified chaperones. The resulting purified ATGL variant demonstrated improved lipolytic activity compared with previously published data, and it could be stimulated by the coactivator protein comparative gene identification-58 and inhibited by the protein G0/G1 switch protein 2. Shock freezing and storage did not affect the basal activity but reduced coactivation of ATGL by comparative gene identification 58. In vitro, the truncated ATGL variant demonstrated acyl-CoA-independent transacylation activity when diacylglycerol was offered as substrate, resulting in the formation of fatty acid as well as triacylglycerol and monoacylglycerol. However, the ATGL variant showed neither hydrolytic activity nor transacylation activity upon offering of monoacylglycerol as substrate. To understand the role of ATGL in different physiological contexts, it is critical for future studies to identify all its different functions and to determine under what conditions these activities occur.

The hsa-miR-214-3p/ATGL axis regulates aberrant lipolysis to promote acute myeloid leukemia progression via PPARα in vitro.

Aberrant lipid metabolism is a hallmark of malignant cancers. Recent studies have shown that abnormal activation of the lipolysis pathway might contribute to acute myeloid leukemia (AML) progression. However, the molecular mechanism through which lipid metabolism mediates AML progression is unknown. RNA-sequencing was used to screen out the target gene pnpla2/ATGL(adipose triglyceride lipase), which showed differential expression in AML. A comparison was made of ATGL mRNA levels in different AML cell lines by real-time PCR. ATGL expression was blocked using siRNAs, and then ATGL expression, proliferation, apoptosis, and cell cycle progression of si-ATGL AML cell lines and si-control AML cell lines were respectively tested. Online tools were used to analyze the potential target microRNAs of ATGL. The mechanism through which hsa-miR-214-3p regulates ATGL was detected by western blotting, proliferation assays, flow cytometry, and dual-luciferase reporter assays. Our results showed that ATGL was overexpressed in AML cell lines. Moreover, ATGL promoted the growth of AML cells. Additionally, hsa-miR-214-3p could suppress ATGL. Finally, we show that hsa-miR-214-3p regulates ATGL through the hsa-miR-214-3p/ATGL/PPARα pathway. This study showed that hsa-miR-214-3p-regulates aberrant lipolysis by promoting ATGL expression, which causes AML progression through the PPARα pathway.

Expression and production of pigment epithelium-derived factor (PEDF) and PEDF receptor variants from mammalian and bacterial cells.

Human SERPINF1 gene codes for pigment epithelium-derived factor (PEDF), a secreted glycoprotein and member of the SERPIN superfamily. To obtain large amounts of recombinant PEDF proteins, we subcloned the coding sequence of human SERPINF1 mutated versions into the pCEP4 vector and generated stably transfected HEK.Ebna cells. The cells produced and secreted recombinant PEDF proteins into the culturing media. The recombinant PEDF proteins were purified by ion-exchange column chromatography and milligram amounts of highly purified protein were recovered. PEDF has affinity for PEDF-receptor (PEDF-R), a membrane-linked lipase encoded by the PNPLA2 gene. Recombinant PEDF-R truncated versions were obtained from Escherichia coli containing expression vectors with human PNPLA2 cDNAs with 3'end deletions and by induction with isopropyl ß-d-1-thiogalactopyranoside. The bacterially derived PEDF-R proteins in insoluble inclusion bodies were solubilized with urea and purified by cation-exchange column chromatography. C-terminally truncated PEDF-R versions containing the ligand binding region retained the ability to bind PEDF. The data demonstrate that mammalian-derived recombinant PEDF and bacterially derived recombinant PEDF-R can be produced and purified in large amounts for further use in structural and biological studies.

PEDF regulates plasticity of a novel lipid-MTOC axis in prostate cancer-associated fibroblasts.

Prostate tumors make metabolic adaptations to ensure adequate energy and amplify cell cycle regulators, such as centrosomes, to sustain their proliferative capacity. It is not known whether cancer-associated fibroblasts (CAFs) undergo metabolic re-programming. We postulated that CAFs augment lipid storage and amplify centrosomal or non-centrosomal microtubule-organizing centers (MTOCs) through a pigment epithelium-derived factor (PEDF)-dependent lipid-MTOC signaling axis. Primary human normal prostate fibroblasts (NFs) and CAFs were evaluated for lipid content, triacylglycerol-regulating proteins, MTOC number and distribution. CAFs were found to store more neutral lipids than NFs. Adipose triglyceride lipase (ATGL) and PEDF were strongly expressed in NFs, whereas CAFs had minimal to undetectable levels of PEDF or ATGL protein. At baseline, CAFs demonstrated MTOC amplification when compared to 1-2 perinuclear MTOCs consistently observed in NFs. Treatment with PEDF or blockade of lipogenesis suppressed lipid content and MTOC number. In summary, our data support that CAFs have acquired a tumor-like phenotype by re-programming lipid metabolism and amplifying MTOCs. Normalization of MTOCs by restoring PEDF or by blocking lipogenesis highlights a previously unrecognized plasticity in centrosomes, which is regulated through a new lipid-MTOC axis.This article has an associated First Person interview with the first author of the paper.

MiRNAs as biomarkers of phenotype in neutral lipid storage disease with myopathy.

BACKGROUND: Neutral lipid storage disease with myopathy (NLSDM) is a rare lipid metabolism disorder. In this study, we evaluated some circulating miRNAs levels in serum samples and the MRI of three affected siblings. METHODS: Three members of one NLSDM family were identified: two brothers and one sister. Muscles of lower and right upper extremities were studied by MRI. Expression profile of miRNAs, obtained from serum samples, was detected using qRT-PCR. RESULTS: Two brothers presented with progressive skeletal myopathy, while the sister had severe hepatosteatosis and diabetes. NLSDM patients showed a significant increase of muscle-specific miRNAs expression compared with healthy subjects. We found a correlation between hepatic damage and elevation of miRNAs expression profile of liver origin. CONCLUSIONS: The dysregulation of miRNAs might represent an indicator of skeletal and hepatic damage and it might be useful to monitor the progression of NLSDM.

Structure-activity relationship studies for the development of inhibitors of murine adipose triglyceride lipase (ATGL).

High serum fatty acid (FA) levels are causally linked to the development of insulin resistance, which eventually progresses to type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) generalized in the term metabolic syndrome. Adipose triglyceride lipase (ATGL) is the initial enzyme in the hydrolysis of intracellular triacylglycerol (TG) stores, liberating fatty acids that are released from adipocytes into the circulation. Hence, ATGL-specific inhibitors have the potential to lower circulating FA concentrations, and counteract the development of insulin resistance and NAFLD. In this article, we report about structure-activity relationship (SAR) studies of small molecule inhibitors of murine ATGL which led to the development of Atglistatin. Atglistatin is a specific inhibitor of murine ATGL, which has proven useful for the validation of ATGL as a potential drug target.

Neutral Lipid Storage Disease Associated with the PNPLA2 Gene: Case Report and Literature Review.

Mutations in the PNPLA2 gene cause neutral lipid storage disease with myopathy (NLSDM) or triglyceride deposit cardiomyovasculopathy. We report a detailed case study of a 53-year-old man with NLSDM. The PNPLA2 gene was analyzed according to the reported method. We summarized the clinical, laboratory, and genetic information of 56 patients, including our patient and 55 other reported patients with homozygous or compound heterozygous mutations in the PNPLA2 gene. We found a novel homozygous mutation (c.194delC) in the PNPLA2 gene that resulted in frameshift. The patient suffered from normal-tension glaucoma and pulmonary cysts, symptoms that are relatively common in the elderly but were not previously reported for this disease. Our summary confirmed that Jordan's anomaly, polymorphonuclear leukocytes with lipid accumulation, was the most consistent finding of this disease. Because this disease is potentially treatable, our results may help rapid and correct diagnosis.

The homozygous variant c.245G > A/p.G82D in PNPLA2 is associated with arrhythmogenic cardiomyopathy phenotypic manifestations.

Arrhythmogenic cardiomyopathy (ACM) is a familial cardiomyopathy featured by fibrofatty replacement of cardiomyocytes. Responsible genetic factors are not discernible in approximately one-third of ACM probands. To investigate this further, we performed whole genome sequencing in 14 mutation-negative ACM probands who underwent cardiac transplantation, and we identified one ACM proband with a rare homozygous missense variant in PNPLA2 (c.245G > A, p.G82D), a rate-limiting enzyme that hydrolyzes triglycerides into fatty acids and diacylglycerol. Bioinformatic analysis suggested that this missense variant may lead to loss of function and therefore impair lipid catabolism. Genetic screening in this proband's family also inferred that the homozygous variant cosegregated with disease. To validate the pathogenicity of this variant and confirm its association with ACM, we established a knockin mouse model carrying the orthologous human homozygous PNPLA2 variant. Interestingly, mice with the homozygous variant presented with arrhythmias and significant cardiac dysfunction at 12 weeks, whereas heterozygous mice were not affected. Moreover, those homozygous mice suffered sudden death and/or heart failure by the age of 14 weeks. Pathological examination showed that extensive lipogenesis in cardiomyocytes and cardiac fibrosis were prominent in the myocardium. Herein, our data demonstrated that the homozygous missense variant PNPLA2 (c.245G > A, p.G82D) associated with a recessive form of ACM.

Long non-coding RNA NEAT1-modulated abnormal lipolysis via ATGL drives hepatocellular carcinoma proliferation.

BACKGROUND: Abnormal metabolism, including abnormal lipid metabolism, is a hallmark of cancer cells. Some studies have demonstrated that the lipogenic pathway might promote the development of hepatocellular carcinoma (HCC). However, the role of the lipolytic pathway in HCC has not been elucidated. METHODS: We compared levels of adipose triglyceride lipase (ATGL) in human HCC and healthy liver tissues by real time PCR, western blot and immunohistochemistry. We measured diacylglycerol(DAG) and free fatty acid (FFA) levels in HCC cells driven by the NEAT1-ATGL axis and in HCC tissues. We also assessed the effects of ATGL, DAG, FFA, and NEAT1 on HCC cells proliferation in vitro and in an orthotopic xenograft HCC mouse model. We also performed a luciferase reporter assay to investigate the interaction between NEAT1/ATGL and miR-124-3p. RESULTS: We found that the lipolytic enzyme, ATGL is highly expressed in human HCC tissues and predicts poor prognosis. We also found that high levels of DAG and FFA are present in HCC tissues. Furthermore, the lncRNA-NEAT1 was found to modulate ATGL expression and disrupt lipolysis in HCC cells via ATGL. Notably, ATGL and its products, DAG and FFA, were shown to be responsible for NEAT1-mediated HCC cell growth. NEAT1 regulated ATGL expression by binding miR-124-3p. Additionally, NEAT1 knockdown attenuated HCC cell growth through miR-124-3p/ATGL/DAG+FFA/PPARα signaling. CONCLUSION: Our results reveal that NEAT1-modulates abnormal lipolysis via ATGL to drive HCC proliferation.

Novel PNPLA2 gene mutation in a child causing neutral lipid storage disease with myopathy.

BACKGROUND: PNPLA2 gene mutations cause neutral lipid storage disease with myopathy (NLSD-M) or cardiomyopathies. The clinical phenotype, blood test results, imaging examination and gene analysis can be used to improve the understanding of NLSD-M, reduce the misdiagnosis rate and prevent physical disability and even premature death. CASE PRESENTATION: We report a Chinese child with NLSD-M presenting with marked asymmetric skeletal myopathy and hypertrophic cardiomyopathy. Blood biochemical tests revealed increased creatine kinase levels, and echocardiography revealed a diffuse and thick left ventricular wall. Gene analysis revealed a homozygous mutation c.155C > G (p.Thr52Arg) in PNPLA2. CONCLUSIONS: An understanding of the characteristic features is essential for the early diagnosis of NLSD-M. Our data expand the allelic spectrum of PNPLA2 mutations, providing further evidence for genetic and clinical NLSD-M heterogeneity in younger individuals.

Generation of induced Pluripotent Stem Cells as disease modelling of NLSDM.

Neutral Lipid Storage Disease with Myopathy (NLSDM) is a rare defect of triacylglycerol metabolism, characterized by the abnormal storage of neutral lipid in organelles known as lipid droplets (LDs). The main clinical features are progressive myopathy and cardiomyopathy. The onset of NLSDM is caused by autosomal recessive mutations in the PNPLA2 gene, which encodes adipose triglyceride lipase (ATGL). Despite its name, this enzyme is present in a wide variety of cell types and catalyzes the first step in triacylglycerol lipolysis and the release of fatty acids. Here, we report the derivation of NLSDM-induced pluripotent stem cells (NLSDM-iPSCs) from fibroblasts of two patients carrying different PNPLA2 mutations. The first patient was homozygous for the c.541delAC, while the second was homozygous for the c.662G>C mutation in the PNPLA2 gene. We verified that the two types of NLSDM-iPSCs possessed properties of embryonic-like stem cells and could differentiate into the three germ layers in vitro. Immunofluorescence analysis revealed that iPSCs had an abnormal accumulation of triglycerides in LDs, the hallmark of NLSDM. Furthermore, NLSDM-iPSCs were deficient in long chain fatty acid lipolysis, when subjected to a pulse chase experiment with oleic acid. Collectively, these results demonstrate that NLSDM-iPSCs are a promising in vitro model to investigate disease mechanisms and screen drug compounds for NLSDM, a rare disease with few therapeutic options.

Neutral lipid-storage disease with myopathy and extended phenotype with novel PNPLA2 mutation.

INTRODUCTION: Neutral lipid-storage disease with myopathy is caused by mutations in PNPLA2, which produce skeletal and cardiac myopathy. We report a man with multiorgan neutral lipid storage and unusual multisystem clinical involvement, including cognitive impairment. METHODS: Quantitative brain MRI with voxel-based morphometry and extended neuropsychological assessment were performed. In parallel, the coding sequences and intron/exon boundaries of the PNPLA2 gene were screened by direct sequencing. RESULTS: Neuropsychological assessment revealed global cognitive impairment, and brain MRI showed reduced gray matter volume in the temporal lobes. Molecular characterization revealed a novel homozygous mutation in exon 5 of PNPLA2 (c.714C>A), resulting in a premature stop codon (p.Cys238*). CONCLUSIONS: Some PNPLA2 mutations, such as the one described here, may present with an extended phenotype, including brain involvement. In these cases, complete neuropsychological testing, combined with quantitative brain MRI, may help to characterize and quantify cognitive impairment.

Peri-conceptional obesogenic exposure induces sex-specific programming of disease susceptibilities in adult mouse offspring.

Vulnerability of the fetus upon maternal obesity can potentially occur during all developmental phases. We aimed at elaborating longer-term health outcomes of fetal overnutrition during the earliest stages of development. We utilized Naval Medical Research Institute (NMRI) mice to induce pre-conceptional and gestational obesity and followed offspring outcomes in the absence of any postnatal obesogenic influences. Male adult offspring developed overweight, insulin resistance, hyperleptinemia, hyperuricemia and hepatic steatosis; all these features were not observed in females. Instead, they showed impaired fasting glucose and a reduced fat mass and adipocyte size. Influences of the interaction of maternal diet∗sex concerned offspring genes involved in fatty liver disease, lipid droplet size regulation and fat mass expansion. These data suggest that a peri-conceptional obesogenic exposure is sufficient to shape offspring gene expression patterns and health outcomes in a sex- and organ-specific manner, indicating varying developmental vulnerabilities between sexes towards metabolic disease in response to maternal overnutrition.

A myopathy with unusual features caused by PNPLA2 gene mutations.

INTRODUCTION: The PNPLA2 gene encodes the enzyme adipose triglyceride lipase (ATGL), which catalyzes the first step of triglyceride hydrolysis. Mutations in this gene are associated with an autosomal recessive lipid-storage myopathy, neutral lipid-storage disease with myopathy (NLSD-M). RESULTS: A 72-year-old woman had late-onset myopathy, with mild weakness, cramps, and exercise intolerance. Electromyography showed myotonic discharges. A few leukocytes showed lipid droplets (Jordan anomaly). Deltoid and quadriceps muscle biopsies showed no lipid storage. Genetic analysis of PNPLA2 detected 2 heterozygous mutations: c.497A>G (p.Asp166Gly) in exon 5 and c.1442C>T (p.Pro481Leu) in exon 10. Expression of mutant PNPLA2 plasmids in HeLa cells resulted in impaired enzyme activity, confirming the pathological effects of the mutations. CONCLUSIONS: In this case of NLSD-M, the myopathy may be due to a metabolic defect rather than to a mechanical effect of lipid storage. This suggests that more than 1 mechanism contributes to muscle damage in NLSD-M.

Dynamics of the Trypanosoma cruzi infection in adipose tissue: Assessing gene expression of PNPLA2, FASN, and ACAT1 under Benzonidazole treatment and indirect mononuclear immune cells interaction.

Trypanosoma cruzi is a parasite with a high capacity to adapt to the host. Animal models have already demonstrated that the tropism of this parasite occurs not only in cardiac/digestive tissues but also in adipose tissue (AT). That said, the consequences ofT. cruziinfection for AT and the implications of treatment with Benzonidazole in this tissue are under discussion. Here, we tested the hypothesis that T. cruzi infection in adipose tissue upon treatment with Benzonidazole (Bz) and the interaction of mononuclear immune cells (PBMC) influences the relative expression of ACAT1, FASN, and PNPLA2 genes. Thus, stem cells derived from adipose tissue (ADSC) after adipogenic differentiation were indirectly cultivated with PBMC after infection with the T. cruzi Y strain and treatment with Bz. We use the TcSAT-IAM system and RT-qPCR to evaluate the parasite load and the relative quantification (ΔCt) of the ACAT1, FASN, and PNPLA2 genes. Our results demonstrate that treatment with Bz did not reduce adipocyte infection in the presence (p-value: 0.5796) or absence (p-value: 0.1854) of cultivation with PBMC. In addition, even though there is no statistical difference when compared to the control group (AT), T. cruzi induces the FASN expression (Rq: 14.00). However, treatment with Bz in AT suggests the increases of PNPLA2 expression levels (Rq: 12.58), even in the absence of T. cruzi infection. During indirect cultivation with PBMC, T. cruzi smooths the expression of PNPLA2 (Rq: 0.824) and instigates the expression of ACAT1 (Rq: 1.632) and FASN (Rq: 1.394). Furthermore, the treatment with Bz during infection induces PNPLA2 expression (Rq: 1.871), maintaining FASN expression levels (Rq: 1.334). Given this, our results indicate that treatment with Benzonidazole did not decrease T. cruzi infection in adipose tissue. However, treating the adipocyte cells with Bz during the interaction with PBMC cells influences the lipid pathways scenario, inducing lipolytic metabolism through the expression of PNPLA2.

Cadmium modulates adipocyte functions in metallothionein-null mice.

Our previous study has demonstrated that exposure to cadmium (Cd), a toxic heavy metal, causes a reduction of adipocyte size and the modulation of adipokine expression. To further investigate the significance of the Cd action, we studied the effect of Cd on the white adipose tissue (WAT) of metallothionein null (MT(-/-)) mice, which cannot form atoxic Cd-MT complexes and are used for evaluating Cd as free ions, and wild type (MT(+/+)) mice. Cd administration more significantly reduced the adipocyte size of MT(-/-) mice than that of MT(+/+) mice. Cd exposure also induced macrophage recruitment to WAT with an increase in the expression level of Ccl2 (MCP-1) in the MT(-/-) mice. The in vitro exposure of Cd to adipocytes induce triglyceride release into culture medium, decrease in the expression levels of genes involved in fatty acid synthesis and lipid hydrolysis at 24 h, and at 48 h increase in phosphorylation of the lipid-droplet-associated protein perilipin, which facilitates the degradation of stored lipids in adipocytes. Therefore, the reduction in adipocyte size by Cd may arise from an imbalance between lipid synthesis and lipolysis. In addition, the expression levels of leptin, adiponectin and resistin decreased in adipocytes. Taken together, exposure to Cd may induce unusually small adipocytes and modulate the expression of adipokines differently from the case of physiologically small adipocytes, and may accelerate the risk of developing insulin resistance and type 2 diabetes.

PNPLA2 mobilizes retinyl esters from retinosomes and promotes the generation of 11-cis-retinal in the visual cycle.

Retinosomes are intracellular lipid bodies found in the retinal pigment epithelium (RPE). They contain retinyl esters (REs) and are thought to be involved in visual chromophore regeneration during dark adaptation and in case of chromophore depletion. However, key enzymes in chromophore regeneration, retinoid isomerase (RPE65), and lecithin:retinol acyltransferase (LRAT) are located in the endoplasmic reticulum (ER). The mechanism and the enzyme responsible for mobilizing REs from retinosomes remained unknown. Our study demonstrates that patatin-like phospholipase domain containing 2 (PNPLA2) mobilizes all-trans-REs from retinosomes. The absence of PNPLA2 in mouse eyes leads to a significant accumulation of lipid droplets in RPE cells, declined electroretinography (ERG) response, and delayed dark adaptation compared with those of WT control mouse. Our work suggests a function of PNPLA2 as an RE hydrolase in the RPE, mobilizing REs from lipid bodies and functioning as an essential component of the visual cycle.