Adipocytes in obesity: A perfect reservoir for SARS-CoV-2?

Research evidence suggests that adipocytes in obesity might facilitate SARS-CoV-2 replication, for it was only found in adipose tissue of individuals with overweight or obesity but not lean individuals who died from COVID-19. As lipid metabolism is key to adipocyte function, and viruses are capable of exploiting and manipulating lipid metabolism of host cells for their own benefit of infection, we hypothesize that adipocytes could not only impair host immune defense against viral infection, but also facilitate SARS-CoV-2 entry, replication and assembly as a reservoir to boost the viral infection in obesity. The latter of which could mainly be mediated by SARS-CoV-2 hijacking the abnormal lipid metabolism in the adipocytes. If these were to be confirmed, an approach to combat COVID-19 in people with obesity by taking advantage of the abnormal lipid metabolism in adipocytes might be considered, as well as modifying lipid metabolism of other host cells as a potential adjunctive treatment for COVID-19.

Genetic predisposition similarities between NASH and ASH: Identification of new therapeutic targets

Fatty liver disease can be triggered by a combination of excess alcohol, dysmetabolism and other environmental cues, which can lead to steatohepatitis and can evolve to acute/chronic liver failure and hepatocellular carcinoma, especially in the presence of shared inherited determinants. The recent identification of the genetic causes of steatohepatitis is revealing new avenues for more effective risk stratification. Discovery of the mechanisms underpinning the detrimental effect of causal mutations has led to some breakthroughs in the comprehension of the pathophysiology of steatohepatitis. Thanks to this approach, hepatocellular fat accumulation, altered lipid droplet remodelling and lipotoxicity have now taken centre stage, while the role of adiposity and gut-liver axis alterations have been independently validated. This process could ignite a virtuous research cycle that, starting from human genomics, through omics approaches, molecular genetics and disease models, may lead to the development of new therapeutics targeted to patients at higher risk. Herein, we also review how this knowledge has been applied to: a) the study of the main PNPLA3 I148M risk variant, up to the stage of the first in-human therapeutic trials; b) highlight a role of MBOAT7 downregulation and lysophosphatidyl-inositol in steatohepatitis; c) identify IL-32 as a candidate mediator linking lipotoxicity to inflammation and liver disease. Although this precision medicine drug discovery pipeline is mainly being applied to non-alcoholic steatohepatitis, there is hope that successful products could be repurposed to treat alcohol-related liver disease as well.

Defatting strategies in the current era of liver steatosis

Liver steatosis is emerging as a major cause of chronic liver disease worldwide, mainly due to the increasing rate of obesity, type 2 diabetes, and metabolic syndrome. Because of the increased incidence of liver steatosis, many organs are currently declined for transplantation despite high demand and waiting list mortality. Defatting strategies have recently emerged as a means of rapidly reducing liver steatosis to expand the pool of available organs. This review summarises advances in defatting strategies in experimental and human models of liver steatosis over the last 20 years.

Stationary phase lipophagy as a cellular mechanism to recycle sterols during quiescence

Delivery of cellular contents to yeast vacuoles/mammalian lysosomes via autophagy ensures long-term cell survival and extends life span. When cultured yeast cells are grown for a prolonged period of time to enter stationary phase, a nondividing state mimicking quiescence, vacuolar membrane proteins partition into either one of the vacuolar microdomains, liquid-ordered (Lo) or liquid-disordered (Ld). We show that during the transition to stationary phase, lipid droplets (LDs), organelles originated from the endoplasmic reticulum (ER), undergo lateral movement to reach the vacuolar surface and are confined within the specific Lo microdomain underlying the network of vacuolar quasi-symmetrical micodomains. Stationary phase lipophagy uses the autophagy machineries to modify the sterol-enriched Lo microdomain to engulf LDs and subsequently deposits the LD-containing vesicles inside the vacuole lumen, which is a pathway morphologically resembling microautophagy. Moreover, stationary phase lipophagy supplies quiescent yeast cells with sterols to sustain phase partitioning of lipids for vacuolar microdomain maintenance. A feed forward loop model was proposed to depict that the sterols boosted by LDs via stationary phase lipophagy promote the Lo microdomain maintenance that in turn stimulates lipophagy.