Perilipin 5 Ameliorates Hepatic Stellate Cell Activation via SMAD2/3 and SNAIL Signaling Pathways and Suppresses STAT3 Activation

Comprehending the molecular mechanisms underlying hepatic fibrogenesis is essential to the development of treatment. The hallmark of hepatic fibrosis is the development and deposition of excess fibrous connective tissue forcing tissue remodeling. Hepatic stellate cells (HSC) play a major role in the pathogenesis of liver fibrosis. Their activation via the transforming growth factor-β1 (TGF-β1) as a key mediator is considered the crucial event in the pathophysiology of hepatic fibrogenesis. It has been shown that Perilipin 5 (PLIN5), known as a lipid droplet structural protein that is highly expressed in oxidative tissue, can inhibit such activation through various mechanisms associated with lipid metabolism. This study aimed to investigate the possible influence of PLIN5 on TGF-β1 signaling. Our findings confirm the importance of PLIN5 in maintaining HSC quiescence in vivo and in vitro. PLIN5 overexpression suppresses the TGF-β1-SMAD2/3 and SNAIL signaling pathways as well as the activation of the signal transducers and activators of transcription 3 (STAT3). These findings derived from experiments in hepatic cell lines LX-2 and Col-GFP, in which overexpression of PLIN5 was able to downregulate the signaling pathways SMAD2/3 and SNAIL activated previously by TGF-β1 treatment. Furthermore, TGF-β1-mediatedinduction of extracellular matrix proteins, such as collagen type I (COL1), Fibronectin, and α-smooth muscle actin (α-SMA), was suppressed by PLIN5. Moreover, STAT3, which is interrelated with TGF-β1 was already basally activated in the cell lines and inhibited by PLIN5 overexpression, leading to a further reduction in HSC activity shown by lowered α-SMA expression. This extension of the intervening mechanisms presents PLIN5 as a potent and pleiotropic target in HSC activation.

Perilipin 5 links mitochondrial uncoupled respiration in brown fat to healthy white fat remodeling and systemic glucose tolerance

Exposure of mice or humans to cold promotes significant changes in brown adipose tissue (BAT) with respect to histology, lipid content, gene expression, and mitochondrial mass and function. Herein we report that the lipid droplet coat protein Perilipin 5 (PLIN5) increases markedly in BAT during exposure of mice to cold. To understand the functional significance of cold-induced PLIN5, we created and characterized gain- and loss-of-function mouse models. Enforcing PLIN5 expression in mouse BAT mimics the effects of cold with respect to mitochondrial cristae packing and uncoupled substrate-driven respiration. PLIN5 is necessary for the maintenance of mitochondrial cristae structure and respiratory function during cold stress. We further show that promoting PLIN5 function in BAT is associated with healthy remodeling of subcutaneous white adipose tissue and improvements in systemic glucose tolerance and diet-induced hepatic steatosis. These observations will inform future strategies that seek to exploit thermogenic adipose tissue as a therapeutic target for type 2 diabetes, obesity, and nonalcoholic fatty liver disease.

MicroRNA-4284 inhibits colon cancer epithelial-mesenchymal transition by down-regulating Perilipin 5

Background: MicroRNA (miR) has been suggested in the development of several types of cancer; yet, the exact function of miR-4284 in colon cancer remains elusive. Methods: MiR-4284 expression was assessed in normal colon cell line CCD-18Co, and HT-29 and SW480 cell lines representing human colon cancer. Potential target gene of miR-4284 was predicted using TargetScanHuman, and experimentally verified using luciferase report assay. Wound-healing, cell invasion and attachment were evaluated to determine the effect of miR-4284 on the migration, invasion, and metastatic properties of colon cancer cell lines. Expression of epithelial-mesenchymal transition (EMT) phenotypic protein hallmarks, including N-cadherin, E-cadherin, as well as Vimentin, was also evaluated. Results: MiR-4284 was significantly decreased in colon cancer cell lines, and Perilipin 5 (PLIN5) was found to be directly targeted by miR-4284. Ectopic expression of miR-4284 significantly reduced endogenous expression level of PLIN5 in colon cancer cell lines, suppressing migration, invasion, and metastatic phenotypes. In addition, re-introducing miR-4284 reversed the expression profile of EMT markers. Conclusion: Our findings for the first time identify miR-4284 as an anti-tumor miRNA in colon cancer, which acts to reduce PLIN5 and inhibit EMT, leading to inhibited colon cancer tumorigenesis. These results highlight the potential of miR-4284 as a therapeutic target in metastatic colon cancer.

LRH-1 Ameliorates Hepatic Triglyceride Accumulation via Regulation of Perilipin 5 in the Liver

Liver receptor homolog-1 (LRH-1) has emerged as a regulator of hepatic glucose, bile acid, and mitochondrial metabolism. However, the functional mechanism underlying the effect of LRH-1 on lipid mobilization has not been addressed. This study investigated the regulatory function of LRH-1 in lipid metabolism during fasting. The wild-type (WT) and LRH-1 liver-specific knockout (LKO) mice were either fed or fasted for 24 h, and the liver and serum were isolated. During fasting, the LRH-1 LKO mice showed greater accumulation of triglycerides in the liver compared to that in WT mice. Interestingly, LRH-1 LKO liver decreased the perilipin 5 (PLIN5) expression and genes involved in β-oxidation. Additionally, the LRH-1 agonist dialauroylphosphatidylcholine also enhanced PLIN5 expression in human cultured HepG2 cells. To identify new target genes of LRH-1, these findings directed to analyze the PLIN5 promoter sequence, which revealed −1620/−1614 to be a putative binding site for LRH-1. This was confirmed by promoter activity and chromatin immuno-precipitation assays. Moreover, fasted WT primary hepatocytes showed increased co-localization of PLIN5 in lipid droplets (LDs) compared to that in fasted LRH-1 LKO primary hepatocytes. Overall, these findings suggest that PLIN5 might be a novel target of LRH-1 to mobilize LDs and manage the cellular needs.

Deletion of Perilipin 5 Protects against Hepatic Injury in Nonalcoholic Fatty Liver Disease via Missing Inflammasome Activation

Nonalcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver diseases with an increasing prevalence due to rising rates of obesity, metabolic syndrome and type II diabetes. Untreated NAFLD may progress to steatohepatitis (NASH) and ultimately liver cirrhosis. NAFLD is characterized by lipid accumulation, and when sufficient excess lipids are obtained, irreversible liver injury may follow. Perilipin 5 (PLIN5), a known lipid droplet coating protein and triglyceride metabolism regulator, is highly expressed in oxidatively modified tissues but it is still unclear how it affects NAFLD/NASH progress. We here studied how PLIN5 affects NAFLD development induced by a 30-week high-fat diet (HFD) administration in wild type and PLIN5 knock out (Plin5−/−) mice. The disruption of PLIN5 induced differences in lipid metabolism during HFD feeding and was associated with reduced hepatic fat accumulation. Surprisingly, Plin5−/− mice showed mitigated activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome, leading to minor hepatic damage. We conclude that PLIN5 is a pleiotropic regulator of hepatic homeostasis in NASH development. Targeting the PLIN5 expression appears critical for protecting the liver from inflammatory activation during chronic NAFLD.