Molecular mechanisms of autophagy and implications in liver diseases

Autophagy is a highly conserved process in which cytosolic contents are degraded by the lysosome,which plays an important role in energy and nutrient balance,and protein or organelle quality control.The liver is the most important organ for metabolism.Studies to date have revealed a significant role of autophagy in the maintenance of liver homeostasis under basal and stressed conditions,and the impairment of autophagy has been closely linked to various liver diseases.Therefore,a comprehensive understanding of the roles of autophagy in liver diseases may help in the development of therapeutic strategies via targeting autophagy.In this review,we will summarize the latest understanding of the molecular mechanisms of autophagy and systematically discuss its implications in various liver diseases,including alcohol-related liver disease,non-alcoholic fatty liver disease,viral hepatitis,hepatocellular carcinoma,and acetaminophen-induced liver injury.

A novel acquired EGFR-SEPT14 fusion confers differential drug resistance to EGFR inhibitors in lung adenocarcinoma

Around 10%-30%of non-small cell lung cancer(NSCLC)patients harbored epidermal growth factor receptor(EGFR)mutations,with L858R and exon-19 deletions(19-Del)accounting for 90%of cases.EGFR tyrosine kinase inhibitors(TKls)showed significant efficacy against common EGFR mutations.However,the therapeutic relevance of uncommon EGFR mutations remained insufficiently investigated.EGFR fusions are extremely rare(0.05%-0.13%)in NSCLC,and Konduri group reported only 5 EGFR fusions from 10,097 patients.i2Additional EGFR'fusions were reported in NSCLC,3,4 all of which were oncogenic drivers and sensitive to EGFR TKls.Herein,we reported an NSCLC patient with leptomeningeal metastasis(LM)who acquired a novel EGFR-SEPT14 fusion during TKI resistance and showed promising responses to certain EGFR TKls and intrathecal pemetrexed(IP).

TMEM251,a new player in lysosomal enzyme trafficking

In recent studies published in Science and Nature Communications,three independent groups identified TMEM251,one transmembrane protein in Golgi,as an indispensable factor for lysosomal enzyme trafficking.Loss or mutation of TMEM251 results in hypersecretion of lysosomal enzymes due to lack of mannose-6-phosphate(M6P)modification,leading to lysosomal dysfunction and eventually lysosome storage disorders(LSDs).The lysosome is a membrane-bound organelle discovered by Christian de Duve in the 1950s.The critical function of lysosome is to degrade and recycle intracellular materials via autophagy and extracellular materials via endocytosis as well as phagocytosis[1].

Donut and spheroid mitochondria: eating, regenerating or trash them out?

In response to stress,mitochondrion undergoes constant morphological changes,including the formation of donut and spheroid mitochondria,and both are believed to be implicated in its biological functions.Mitochondria are critical for cellular metabolic homeostasis and cell survival and death in eukaryotic cells.Mitochondria are dynamic organelles that constantly undergo fission and fusion.Mitochondrial homeostasis is tightly regulated by mitophagy for the removal of damaged or excess mitochondria and by mitochondria biogenies of new mitochondria.Mitochondria can also undergo other morphological transformation,such as formation of donut-like mitochondria or mitochondrial spheroids,and can also be secreted into the extracellular spaces.Here we discuss the mechanistic insights and physiological relevance of the donut-like mitochondria or mitochondrial spheroids and the secretion of mitochondria in cell biology.

CLN3 clinches lysosomes in clearance of glycerophospholipids

CLN3 is a lysosomal transmembrane protein and loss of CLN3 is known to cause a juvenile lethal neurodegenerative lysosomal storage disorder(LSD),called Batten disease.In a recent study published in Nature,Laqtom et al.reported a novel function of CLN3 in the clearance of glycerophospholipid from lysosomes via lysosomal efflux of glycerophosphodiesters(GPDs),not only establishing a deeper mechanistic understanding of Batten disease,but also suggesting both the diagnostic and therapeutic potential of CLN3-GPDs in this type of neurodegenerative LSD.

Celastrol induces ferroptosis in activated HSCs to ameliorate hepatic fibrosis via targeting peroxiredoxins and HO-1

Ferroptosis is a form of regulated cell death, characterized by excessive membrane lipid peroxidation in an iron-and ROS-dependent manner. Celastrol, a natural bioactive triterpenoid extracted from Tripterygium wilfordii, shows effective anti-fibrotic and anti-inflammatory activities in multiple hepatic diseases. However, the exact molecular mechanisms of action and the direct protein targets of celastrol in the treatment of liver fibrosis remain largely elusive. Here, we discover that celastrol exerts anti-fibrotic effects via promoting the production of reactive oxygen species(ROS) and inducing ferroptosis in activated hepatic stellate cells(HSCs). By using activity-based protein profiling(ABPP) in combination with bio-orthogonal click chemistry reaction and cellular thermal shift assay(CETSA), we show that celastrol directly binds to peroxiredoxins(PRDXs), including PRDX1, PRDX2, PRDX4 and PRDX6,through the active cysteine sites, and inhibits their anti-oxidant activities. Celastrol also targets to heme oxygenase 1(HO-1) and upregulates its expression in activated-HSCs. Knockdown of PRDX1, PRDX2,PRDX4, PRDX6 or HO-1 in HSCs, to varying extent, elevated cellular ROS levels and induced ferroptosis. Taken together, our findings reveal the direct protein targets and molecular mechanisms via which celastrol ameliorates hepatic fibrosis, thus supporting the further development of celastrol as a promising therapeutic agent for liver fibrosis.

Impairment of the autophagy-lysosomal pathway in Alzheimer’s diseases: Pathogenic mechanisms and therapeutic potential

Alzheimer’s disease(AD),the most common neurodegenerative disorder,is characterized by memory loss and cognitive dysfunction.The accumulation of misfolded protein aggregates including amyloid beta(Aβ)peptides and microtubule associated protein tau(MAPT/tau)in neuronal cells are hallmarks of AD.So far,the exact underlying mechanisms for the aetiologies of AD have not been fully understood and the effective treatment for AD is limited.Autophagy is an evolutionarily conserved cellular catabolic process by which damaged cellular organelles and protein aggregates are degraded via lysosomes.Recently,there is accumulating evidence linking the impairment of the autophagy-lysosomal pathway with AD pathogenesis.Interestingly,the enhancement of autophagy to remove protein aggregates has been proposed as a promising therapeutic strategy for AD.Here,we first summarize the recent genetic,pathological and experimental studies regarding the impairment of the autophagy-lysosomal pathway in AD.We then describe the interplay between the autophagy-lysosomal pathway and two pathological proteins,Aβand MAPT/tau,in AD.Finally,we discuss potential therapeutic strategies and small molecules that target the autophagy-lysosomal pathway for AD treatment both in animal models and in clinical trials.Overall,this article highlights the pivotal functions of the autophagy-lysosomal pathway in AD pathogenesis and potential druggable targets in the autophagy-lysosomal pathway for AD treatment.

Ticagrelor inhibits the NLRP3 inflammasome to protect against inflammatory disease independent of the P2Y_(12 ) signaling pathway

Ticagrelor is the first reversibly binding oralP2Y_(12) receptor antagonist to inhibit platelet activation and has been approved by the Food and Drug Administration for the treatment of coronary artery disease. At present, the other pharmacological functions of ticagrelor remain poorly understood. The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome plays a critical role in the innate immune system, but its excessive activation also contributes to the pathogenesis of complex diseases. In this study, we systematically examined the effects of ticagrelor on the NLRP3 inflammasome and found that ticagrelor inhibits NLRP3 inflammasome activation in macrophages independent of its classic inhibitory effect on theP2Y_(12) signaling pathway. Further mechanistic studies demonstrate that ticagrelor attenuates the oligomerization of apoptosis-associated speck-like protein containing a CARD (ASC) by blocking chloride efflux, an effect achieved through the degradation of chloride intracellular channel proteins (CLICs) and blockade of the translocation of CLICs to the plasma membrane. Moreover, experiments on lipopolysaccharide-induced sepsis and alum-induced peritonitis in mice confirmed that ticagrelor mitigates the severity of systemic inflammation independent ofP2Y_(12) receptor antagonism. Importantly, oral administration of ticagrelor rapidly and strongly inhibited NLRP3 inflammasome activation in peripheral blood mononuclear cells from patients with acute coronary syndrome. Overall, our study reveals a novel pharmacological function of ticagrelor in addition to its classic antiplatelet properties, which suggests that ticagrelor may serve as a potential therapeutic agent for use in NLRP3-associated diseases.

Photodynamic therapy accelerates skin wound healing through promoting re-epithelialization

Background:Epidermal stem cells(EpSCs)that reside in cutaneous hair follicles and the basal layer of the epidermis are indispensable for wound healing and skin homeostasis.Little is known about the effects of photochemical activation on EpSC differentiation,proliferation and migration during wound healing.The present study aimed to determine the effects of photodynamic therapy(PDT)on wound healing in vivo and in vitro.Methods:We created mouse full-thickness skin resection models and applied 5-aminolevulinic acid(ALA)for PDT to the wound beds.Wound healing was analysed by gross evaluation and haematoxylin–eosin staining in vivo.In cultured EpSCs,protein expression was measured using flow cytometry and immunohistochemistry.Cell migration was examined using a scratch model;apoptosis and differentiation were measured using flow cytometry.Results:PDT accelerated wound closure by enhancing EpSC differentiation,proliferation and migration,thereby promoting re-epithelialization and angiogenesis.PDT inhibited inflammatory infiltration and expression of proinflammatory cytokines,whereas the secretion of growth factors was greater than in other groups.The proportion of transient amplifying cells was significantly greater in vivo and in vitro in the PDT groups.EpSC migration was markedly enhanced after ALAinduced PDT.Conclusions:Topical ALA-induced PDT stimulates wound healing by enhancing re-epithelialization,promoting angiogenesis as well as modulating skin homeostasis.This work provides a preliminary theoretical foundation for the clinical administration of topical ALA-induced PDT in skin wound healing.

Synergistic effects of autophagy/mitophagy inhibitors and magnolol promote apoptosis and antitumor efficacy

Mitochondria as a signaling platform play crucial roles in deciding cell fate.Many classic anticancer agents are known to trigger cell death through induction of mitochondrial damage.Mitophagy,one selective autophagy,is the key mitochondrial quality control that effectively removes damaged mitochondria.However,the precise roles of mitophagy in tumorigenesis and anticancer agent treatment remain largely unclear.Here,we examined the functional implication of mitophagy in the anticancer properties of magnolol,a natural product isolated from herbal Magnolia officinalis.First,we found that magnolol induces mitochondrial depolarization,causes excessive mitochondrial fragmentation,and increases mitochondrial reactive oxygen species(mtROS).Second,magnolol induces PTEN-induced putative kinase protein 1(PINK1)-Parkin-mediated mitophagy through regulating two positive feedforward amplification loops.Third,magnolol triggers cancer cell death and inhibits neuroblastoma tumor growth via the intrinsic apoptosis pathway.Moreover,magnolol prolongs the survival time of tumor-bearing mice.Finally,inhibition of mitophagy by PINK1/Parkin knockdown or using inhibitors targeting different autophagy/mitophagy stages significantly promotes magnolol-induced cell death and enhances magnolol's anticancer efficacy,both in vitro and in vivo.Altogether,our study demonstrates that magnolol can induce autophagy/mitophagy and apoptosis,whereas blockage of autophagy/mitophagy remarkably enhances the anticancer efficacy of magnolol,suggesting that targeting mitophagy may be a promising strategy to overcome chemoresistance and improve anticancer therapy.

P311 promotes typeⅡtransforming growth factor-βreceptor mediated fibroblast activation and granulation tissue formation in wound healing

Background:P311,a highly conserved 8 kDa intracellular protein,has recently been reported to play an important role in aggravating hypertrophic scaring by promoting the differentiation and secretion of fibroblasts.Nevertheless,how P311 regulates the differentiation and function of fibroblasts to affect granulation tissue formation remains unclear.In this work,we studied the underlying mechanisms via which P311 affects fibroblasts and promotes acute skin wound repair.Methods:To explore the role of P311,both in vitro and in vivo wound-healing models were used.Full-thickness skin excisional wounds were made in wild-type and P311−/−C57 adult mice.Wound healing rate,re-epithelialization,granulation tissue formation and collagen deposition were measured at days 3,6 and 9 after skin injury.The biological phenotypes of fibroblasts,the expression of target proteins and relevant signaling pathways were examined both in vitro and in vivo.Results:P311 could promote the proliferation and differentiation of fibroblasts,enhance the ability of myofibroblasts to secrete extracellular matrix and promote cell contraction,and then facilitate the formation of granulation tissue and eventually accelerate skin wound closure.Importantly,we discovered that P311 acts via up-regulating the expression of type II transforming growth factor-βreceptor(TGF-βRII)in fibroblasts and promoting the activation of the TGF-βRII-Smad signaling pathway.Mechanistically,the mammalian target of rapamycin signaling pathway is closely implicated in the regulation of the TGF-βRII-Smad pathway in fibroblasts mediated by P311.Conclusions:P311 plays a critical role in activation of the TGF-βRII-Smad pathway to promote fibroblast proliferation and differentiation as well as granulation tissue formation in the process of skin wound repair.