Yan-Xiao Ji

The long noncoding RNA Chaer defines an epigenetic checkpoint in cardiac hypertrophy.

Epigenetic reprogramming is a critical process of pathological gene induction during cardiac hypertrophy and remodeling, but the underlying regulatory mechanisms remain to be elucidated. Here we identified a heart-enriched long noncoding (lnc)RNA, named cardiac-hypertrophy-associated epigenetic regulator (Chaer), which is necessary for the development of cardiac hypertrophy. Mechanistically, Chaer directly interacts with the catalytic subunit of polycomb repressor complex 2 (PRC2). This interaction, which is mediated by a 66-mer motif in Chaer, interferes with PRC2 targeting to genomic loci, thereby inhibiting histone H3 lysine 27 methylation at the promoter regions of genes involved in cardiac hypertrophy. The interaction between Chaer and PRC2 is transiently induced after hormone or stress stimulation in a process involving mammalian target of rapamycin complex 1, and this interaction is a prerequisite for epigenetic reprogramming and induction of genes involved in hypertrophy. Inhibition of Chaer expression in the heart before, but not after, the onset of pressure overload substantially attenuates cardiac hypertrophy and dysfunction. Our study reveals that stress-induced pathological gene activation in the heart requires a previously uncharacterized lncRNA-dependent epigenetic checkpoint.

The ubiquitin E3 ligase TRAF6 exacerbates pathological cardiac hypertrophy via TAK1-dependent signalling

Tumour necrosis factor receptor-associated factor 6 (TRAF6) is a ubiquitin E3 ligase that regulates important biological processes. However, the role of TRAF6 in cardiac hypertrophy remains unknown. Here, we show that TRAF6 levels are increased in human and murine hypertrophied hearts, which is regulated by reactive oxygen species (ROS) production. Cardiac-specific Traf6 overexpression exacerbates cardiac hypertrophy in response to pressure overload or angiotensin II (Ang II) challenge, whereas Traf6 deficiency causes an alleviated hypertrophic phenotype in mice. Mechanistically, we show that ROS, generated during hypertrophic progression, triggers TRAF6 auto-ubiquitination that facilitates recruitment of TAB2 and its binding to transforming growth factor beta-activated kinase 1 (TAK1), which, in turn, enables the direct TRAF6–TAK1 interaction and promotes TAK1 ubiquitination. The binding of TRAF6 to TAK1 and the induction of TAK1 ubiquitination and activation are indispensable for TRAF6-regulated cardiac remodelling. Taken together, we define TRAF6 as an essential molecular switch leading to cardiac hypertrophy in a TAK1-dependent manner.

Targeting CASP8 and FADD-like apoptosis regulator ameliorates nonalcoholic steatohepatitis in mice and nonhuman primates

Nonalcoholic steatohepatitis (NASH) is a progressive disease that is often accompanied by metabolic syndrome and poses a high risk of severe liver damage. However, no effective pharmacological treatment is currently available for NASH. Here we report that CASP8 and FADD-like apoptosis regulator (CFLAR) is a key suppressor of steatohepatitis and its metabolic disorders. We provide mechanistic evidence that CFLAR directly targets the kinase MAP3K5 (also known as ASK1) and interrupts its N-terminus-mediated dimerization, thereby blocking signaling involving ASK1 and the kinase MAPK8 (also known as JNK1). Furthermore, we identified a small peptide segment in CFLAR that effectively attenuates the progression of steatohepatitis and metabolic disorders in both mice and monkeys by disrupting the N-terminus-mediated dimerization of ASK1 when the peptide is expressed from an injected adenovirus-associated virus 8–based vector. Taken together, these findings establish CFLAR as a key suppressor of steatohepatitis and indicate that the development of CFLAR-peptide-mimicking drugs and the screening of small-molecular inhibitors that specifically block ASK1 dimerization are new and feasible approaches for NASH treatment.

Tmbim1 is a multivesicular body regulator that protects against non-alcoholic fatty liver disease in mice and monkeys by targeting the lysosomal degradation of Tlr4

Non-alcoholic steatohepatitis (NASH) is an increasingly prevalent liver pathology that can progress from non-alcoholic fatty liver disease (NAFLD), and it is a leading cause of cirrhosis and hepatocellular carcinoma. There is currently no pharmacological therapy for NASH. Defective lysosome-mediated protein degradation is a key process that underlies steatohepatitis and a well-recognized drug target in a variety of diseases; however, whether it can serve as a therapeutic target for NAFLD and NASH remains unknown. Here we report that transmembrane BAX inhibitor motif-containing 1 (TMBIM1) is an effective suppressor of steatohepatitis and a previously unknown regulator of the multivesicular body (MVB)-lysosomal pathway. Tmbim1 expression in hepatocytes substantially inhibited high-fat diet–induced insulin resistance, hepatic steatosis and inflammation in mice. Mechanistically, Tmbim1 promoted the lysosomal degradation of toll-like receptor 4 by cooperating with the ESCRT endosomal sorting complex to facilitate MVB formation, and the ubiquitination of Tmbim1 by the E3 ubiquitin ligase Nedd4l was required for this process. We also found that overexpression of Tmbim1 in the liver effectively inhibited a severe form of NAFLD in mice and NASH progression in monkeys. Taken together, these findings could lead to the development of promising strategies to treat NASH by targeting MVB regulators to properly orchestrate the lysosome-mediated protein degradation of key mediators of the disease.

Suppressor of IKKɛ is an essential negative regulator of pathological cardiac hypertrophy

Although pathological cardiac hypertrophy represents a leading cause of morbidity and mortality worldwide, our understanding of the molecular mechanisms underlying this disease is still poor. Here, we demonstrate that suppressor of IKKɛ (SIKE), a negative regulator of the interferon pathway, attenuates pathological cardiac hypertrophy in rodents and non-human primates in a TANK-binding kinase 1 (TBK1)/AKT-dependent manner. Sike-deficient mice develop cardiac hypertrophy and heart failure, whereas Sike-overexpressing transgenic (Sike-TG) mice are protected from hypertrophic stimuli. Mechanistically, SIKE directly interacts with TBK1 to inhibit the TBK1-AKT signalling pathway, thereby achieving its anti-hypertrophic action. The suppression of cardiac remodelling by SIKE is further validated in rats and monkeys. Collectively, these findings identify SIKE as a negative regulator of cardiac remodelling in multiple animal species due to its inhibitory regulation of the TBK1/AKT axis, suggesting that SIKE may represent a therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Tumor necrosis factor receptor-associated factor 5 (Traf5) acts as an essential negative regulator of hepatic steatosis

BACKGROUND & AIMS Obesity-related metabolic inflammation, insulin resistance (IR), and excessive fat accumulation are linked phenomena that promote the progression of nonalcoholic fatty liver disease (NAFLD). Previous research has indicated that CD40-TRAF5 signaling protects against obesity-related metabolic disorders; however, the precise roles and underlying mechanisms of TRAF5 in obesity-induced pathological processes have not been fully elucidated. METHODS TRAF5 expression was evaluated in the livers of NAFLD patients, high-fat diet (HFD)-induced or genetically (ob/ob) induced obese mice, and in palmitate-treated hepatocytes. Gain- or loss-of-function approaches were used to investigate the specific roles and mechanisms of hepatic Traf5 under obesity-related pathological conditions. RESULTS TRAF5 expression was decreased in the fatty livers of both NAFLD patients and obese mice, and in palmitate-treated hepatocytes in vitro. Traf5 overexpression significantly suppressed nonalcoholic steatohepatitis (NASH)-like phenotypes in mice after HFD treatment for 24weeks and inhibited the progression of NAFLD in ob/ob mice. Conversely, Traf5 deficiency resulted in the deterioration of metabolic disorders induced by HFD. Investigations of the underlying mechanisms revealed that Traf5 regulates hepatic steatosis by targeting Jnk signaling. Specifically, Jnk1 rather than Jnk2 is responsible for the function of Traf5 in metabolic disorders, as evidenced by the fact that Jnk1 ablation markedly ameliorates the detrimental effects of Traf5 deficiency on obesity, inflammation, IR, hepatic steatosis and fibrosis. CONCLUSIONS Traf5 negatively regulates NAFLD/NASH and related metabolic dysfunctions by blocking Jnk1 activity, which represents a potential therapeutic target for obesity-related metabolic disorders. LAY SUMMARY Lipid accumulation in the liver induces degradation of Traf5. Increasing Traf5 ameliorates nonalcoholic fatty liver by blocking Jnk1 activity.

The deubiquitinating enzyme TNFAIP3 mediates inactivation of hepatic ASK1 and ameliorates nonalcoholic steatohepatitis

Activation of apoptosis signal-regulating kinase 1 (ASK1) in hepatocytes is a key process in the progression of nonalcoholic steatohepatitis (NASH) and a promising target for treatment of the condition. However, the mechanism underlying ASK1 activation is still unclear, and thus the endogenous regulators of this kinase remain open to be exploited as potential therapeutic targets. In screening for proteins that interact with ASK1 in the context of NASH, we identified the deubiquitinase tumor necrosis factor alpha–induced protein 3 (TNFAIP3) as a key endogenous suppressor of ASK1 activation, and we found that TNFAIP3 directly interacts with and deubiquitinates ASK1 in hepatocytes. Hepatocyte-specific ablation of Tnfaip3 exacerbated nonalcoholic fatty liver disease– and NASH-related phenotypes in mice, including glucose metabolism disorders, lipid accumulation and enhanced inflammation, in an ASK1-dependent manner. In contrast, transgenic or adeno-associated virus–mediated TNFAIP3 gene delivery in the liver in both mouse and nonhuman primate models of NASH substantially blocked the onset and progression of the disease. These results implicate TNFAIP3 as a functionally important endogenous suppressor of ASK1 hyperactivation in the pathogenesis of NASH and identify it as a potential new molecular target for NASH therapy.

Tripartite Motif 32 Prevents Pathological Cardiac Hypertrophy

This study presents the first evidence that TRIM32 protects against pathological cardiac hypertrophy by suppressing Akt-dependent signalling pathways. Therefore TRIM32 might be a potential therapeutic strategy for the prevention and treatment of cardiac hypertrophy and heart failure.

The E3 ligase tripartite motif 8 targets TAK1 to promote insulin resistance and steatohepatitis

Tripartite motif 8 (TRIM8), an E3 ligase ubiquitously expressed in various cells, is closely involved in innate immunity. However, its role in nonalcoholic steatohepatitis is largely unknown. Here, we report evidence that TRIM8 is a robust enhancer of steatohepatitis and its complications induced by a high‐fat diet or a genetic deficiency (ob/ob). Using gain‐of‐function and loss‐of‐function approaches, we observed dramatic exacerbation of insulin resistance, hepatic steatosis, inflammation, and fibrosis by hepatocyte‐specific TRIM8 overexpression, whereas deletion or down‐regulation of TRIM8 in hepatocytes led to a completely opposite phenotype. Furthermore, investigations of the underlying mechanisms revealed that TRIM8 directly binds to and ubiquitinates transforming growth factor‐beta–activated kinase 1, thus promoting its phosphorylation and the activation of downstream c‐Jun N‐terminal kinase/p38 and nuclear factor κB signaling. Importantly, the participation of TRIM8 in human nonalcoholic fatty liver disease and nonalcoholic steatohepatitis was verified on the basis of its dramatically increased expression in the livers of these patients, suggesting a promising development of TRIM8 disturbance for the treatment of nonalcoholic steatohepatitis–related metabolic disorders. Conclusion: The E3 ligase TRIM8 is a potent regulator that exacerbates steatohepatitis and metabolic disorders dependent on its binding and ubiquitinating capacity on transforming growth factor‐beta–activated kinase 1. (Hepatology 2017;65:1492‐1511)

The deubiquitinating enzyme cylindromatosis mitigates nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a common clinical condition that can lead to advanced liver diseases. Lack of effective pharmacotherapies for NASH is largely attributable to an incomplete understanding of its pathogenesis. The deubiquitinase cylindromatosis (CYLD) plays key roles in inflammation and cancer. Here we identified CYLD as a suppressor of NASH in mice and in monkeys. CYLD is progressively degraded upon interaction with the E3 ligase TRIM47 in proportion to NASH severity. We observed that overexpression of Cyld in hepatocytes concomitantly inhibits lipid accumulation, insulin resistance, inflammation and fibrosis in mice with NASH induced in an experimental setting. Mechanistically, CYLD interacts directly with the kinase TAK1 and removes its K63-linked polyubiquitin chain, which blocks downstream activation of the JNK–p38 cascades. Notably, reconstitution of hepatic CYLD expression effectively reverses disease progression in mice with dietary or genetically induced NASH and in high-fat diet–fed monkeys predisposed to metabolic syndrome. Collectively, our findings demonstrate that CYLD mitigates NASH severity and identify the CYLD–TAK1 axis as a promising therapeutic target for management of the disease.