Rab proteins implicated in lipid storage and mobilization

Abnormal intracellular accumulation or transport of lipids contributes greatly to the pathogenesis of human diseases. In the liver, excess accumulation of triacylglycerol （TG） leads to fatty liver disease encompassing steatosis, steatohepatitis and fibrosis. This places individuals at risk of developing cirrhosis, hepatocellular carcinoma or hepatic decompensation and also contributes to the emergence of insulin resistance and dyslipidemias affecting many other organs. Excessive accumulation of TG in adipose tissue contributes to insulin resistance as well as to the release of cytokines attracting leucocytes leading to a pro-inflammatory state. Pathological accumulation of cholesteryl ester （CE） in macrophages in the arterial wall is the progenitor of atherosclerotic plaques and heart disease. Overconsumption of dietary fat, cholesterol and carbohydrates explains why these diseases are on the increase yet offers few clues for how to prevent or treat individuals. Dietary regimes have proven futile and barfing surgery, no realistic alternatives are at hand as effective drugs are few and not without side effects. Overweight and obesity-related diseases are no longer restricted to the developed world and as such, constitute a global problem. Development of new drugs and treatment strategies are a priority yet requires as a first step, elucidation of the molecular pathophysiology underlying each associated disease state. The lipid droplet （LD）, an up to now over- looked intracellular organelle, appears at the heart of each pathophysiology linking key regulatory and metabolic processes as well as constituting the site of storage of both TGs and CEs. As the molecular machinery and mechanisms of LDs of each cell type are being elucidated, regulatory proteins used to control various cellular processes are emerging. Of these and the subject of this review, small GTPases belonging to the Rab protein family appear as important molecular switches used in the regulation of the intracellular trafficking and storage of lipids.

Inhibition of YIPF2 Improves the Vulnerability of Oligodendrocytes to Human Islet Amyloid Polypeptide

Excessive secretion of human islet amyloid polypeptide(hIAPP)is an important pathological basis of diabetic encephalopathy(DE).In this study,we aimed to investigate the potential implications of hIAPP in DE pathogenesis.Brain magnetic resonance imaging and cognitive scales were applied to evaluate white matter damage and cognitive function.We found that the concentration of serum hIAPP was positively correlated with white matter damage but negatively correlated with cognitive scores in patients with type 2 diabetes mellitus.In vitro assays revealed that oligodendrocytes,compared with neurons,were more prone to acidosis under exogenous hIAPP stimulation.Moreover,western blotting and co-immunoprecipitation indicated that hIAPP interfered with the binding process of monocarboxylate transporter(MCT)1 to its accessory protein CD147 but had no effect on the binding of MCT2 to its accessory protein gp70.Proteomic differential analysis of proteins co-immunoprecipitated with CD147 in oligodendrocytes revealed Yeast Rab GTPase-Interacting protein 2(YIPF2,which modulates the transfer of CD147 to the cell membrane)as a significant target.Furthermore,YIPF2 inhibition significantly improved hIAPP-induced acidosis in oligodendrocytes and alleviated cognitive dysfunction in DE model mice.These findings suggest that increased CD147 translocation by inhibition of YIPF2 optimizes MCT1 and CD147 binding,potentially ameliorating hIAPP-induced acidosis and the consequent DE-related demyelination.

Apoptotic vesicles rejuvenate mesenchymal stem cells via Rab7-mediated autolysosome formation and alleviate bone loss in aging mice

Aging skeletons display decreased bone mass,increased marrow adiposity,and impaired bone marrow mesenchymal stem cells(MSCs).Apoptosis is a programmed cell death process that generates a large number of apoptotic vesicles(apoVs).Dysregulated apoptosis has been closely linked to senescence-associated diseases.However,whether apoVs mediate agingrelated bone loss is not clear.In this study,we showed that young MSC-derived apoVs effectively rejuvenated the nuclear abnormalities of aged bone marrow MSCs and restored their impaired self-renewal,osteo-/adipo-genic lineage differentiation capacities via activating autophagy.Mechanistically,apoptotic young MSCs generated and enriched a high level of Ras-related protein 7(Rab7)into apoVs.Subsequently,recipient aged MSCs reused apoV-derived Rab7 to restore autolysosomes formation,thereby contributing to autophagy flux activation and MSC rejuvenation.Moreover,systemic infusion of young MSC-derived apoVs enhanced bone mass,reduced marrow adiposity,and recused the impairment of recipient MSCs in aged mice.Our findings reveal the role of apoVs in rejuvenating aging-MSCs via restoring autolysosome formation and provide a potential approach for treating age-related bone loss.