ATG14 plays a critical role in hepatic lipid droplet homeostasis

A phloem-limited unculturable bacterium induces mild xenophagy in insect vectors for persistent infection

Xenophagy is an important antibacterial defense mechanism that many organisms use to engulf intracellular pathogens. However, the mechanisms of xenophagy triggered by insect-borne plant bacteria are not well understood. Candidatus Liberibacter asiaticus (CLas) causes Huanglongbing, which poses a serious threat to citrus production. CLas is a phloem-limited unculturable bacterium that is transmitted by the Asian citrus psyllid in a persistent and propagative manner in nature. Here, we found that CLas infection in the gut of psyllids triggered a mild and anti-bacterial xenophagy. Xenophagy limited excessive propagation of CLas to maintain psyllid survival, because overload of CLas was detrimental to psyllid life. Furthermore, the outer membrane β-barrel protein (OMBB) of CLas is the key secreted protein that induces xenophagy in psyllids by interacting with ATG8 and ATG14. OMBB can independently induce autophagy in psyllid and non-host cells. Together, these results revealed that an insect-borne plant bacterium activates mild xenophagy to control its propagation, thereby achieving persistent infection in insect vectors.

Hepatic Klf10-Fh1 axis promotes exercise-mediated amelioration of NASH in mice

Exercise is an effective non-pharmacological strategy for the treatment of nonalcoholic steatohepatitis (NASH), but the underlying mechanism needs further investigation. Kruppel-like factor 10 (Klf10) is a transcriptional factor that is expressed in multiple tissues including liver, whose role in NASH is not well defined. In our study, exercise induces hepatic Klf10 expression through the cAMP/PKA/CREB pathway. Hepatocyte-specific knockout of Klf10 (Klf10LKO) increases lipid accumulation, cell death, inflammation and fibrosis in NASH diet-fed mice and reduces the protective effects of treadmill exercise against NASH, while hepatocyte-specific overexpression of Klf10 (Klf10LTG) works in concert with exercise to reduce NASH in mice. Mechanistically, Klf10 promotes the expression of fumarate hydratase 1 (Fh1), thereby reducing fumarate accumulation in hepatocytes. This decreases the trimethyl (me3) levels of histone 3 lysine 4 (H3K4me3) on lipogenic genes promoters to attenuate lipogenesis, thus ameliorating free fatty acids (FFAs)-induced hepatocytes steatosis, apoptosis, insulin resistance and blunting dysfunctional hepatocytes-mediated activation of macrophages and hepatic stellate cells. Therefore, by regulating the Fh1/fumarate/H3K4me3 pathway, Klf10 acts as a downstream effector of exercise to combat NASH.

Lipid droplets in steatotic liver disease

PURPOSE OF REVIEW

This review aims to discuss the most recent evidence exploring the role of lipid droplets in steatotic liver disease (SLD). We highlight the breadth of mechanisms by which lipid droplets may contribute to the progression of SLD with a particular focus on the role of lipid droplets as inducers of mechanical stress within hepatocytes and genetic mutations in lipid droplet associated proteins. Finally, this review provides an update on clinical trials exploring the therapeutic potential and strategies targeting lipid droplets.

RECENT FINDINGS

The size, composition and location of hepatic lipid droplets strongly influence the pathological role of these organelles in SLD. Emerging studies are beginning to elucidate the importance of lipid droplet induced hepatocyte mechanical stress. Novel strategies targeting lipid droplets, including the effects of lipid droplet associated protein mutations, show promising therapeutic potential.

SUMMARY

Much more than a histological feature, lipid droplets are complex heterogenous organelles crucial to cellular metabolism with important causative roles in the development and progression of SLD. Lipid droplet induced mechanical stress may exacerbate hepatic inflammation and fibrogenesis and potentially contribute to the development of a pro-carcinogenic hepatic environment. The integration of advancements in genetics and molecular biology in upcoming treatments aspires to transcend symptomatic alleviation and address the fundamental causes and pathological development of SLD.