Ling Zheng

Muscle regenerative capacity declines with aging and disease, which leads to muscle loss and reduced lifespan. Muscle regenerative failure is related to a disrupted network orchestrated by multiple muscle-harbored cell types; whether and how the interplay between macrophages and myofibers contributes to this process is largely unknown. Herein, we report upregulation of histone methyltransferase G9a in both aged human muscle and mouse muscle after injury. Deletion of G9a in either myeloid cells or myofibers accelerates muscle regeneration. Mechanistically, G9a down-regulates macrophage-derived interleukin 13 (IL13) and suppresses myofiber-derived myokine musclin, respectively, to inhibit myogenesis and macrophage phenotype transition during muscle regeneration. Either IL13 or musclin, per se, accelerated muscle regeneration, and their combined administration showed synergistic effects with therapeutic potentials for muscle degeneration disorders. Collectively, we highlight a crosstalk between macrophages and myofibers through IL13-Stat6 signaling and musclin, both regulated by G9a, which steers a pro-recovery microenvironment after muscle injury, with therapeutic potentials for muscle degeneration disorders.

Fasting-induced metabolic remodeling is a fundamental process maintaining systemic homeostasis, with profound implications for metabolic disease interventions. During fasting, liver establishes a regulatory network centered on gluconeogenesis that integrates major fuels to keep physiological energy homeostasis. Here, we report that GAPDH, a key enzyme in both glycolysis and gluconeogenesis, senses fasting stress in the liver. Compared to wildtype controls, hepatocyte Gapdh deficiency (Gap^Alb) mice show comparable blood glucose, decreased amino acid levels and aggravated lipid accumulation in the liver after overnight fasting. Mechanistically, Gapdh depletion decreases serine levels, and serine supplementation inhibits PA-DAG (phosphatidic acid-diacylglycerols) axis by downregulating Lipin1 (a phosphohydrolase in DAG synthesis) upon overnight fasting. Furthermore, knockdown of Lipin1 rescued the effects observed in fasted Gap^Alb mice. Similarly, Gap^Alb mice showed enhanced hepatic lipid accumulation under ketogenic diets, and serine supplementation abolished these effects. Together, we find hepatic GAPDH as a central hub in glucose-amino acid-fat metabolism during nutritional limitation.

UTX (also known as KDM6A) is a histone H3K27 demethylase that acts as an important tumor regulator. UTX has been reported to participate in genome‐wide histone modifications and gene expression in tumorigenesis and its mutations are identified in human cancers. Here, UTX is demonstrated to localize both in the cytoplasm and nucleus, notably, cytoplasmic UTX forms puncta and co‐localizes in stress granules (SGs) upon different stresses in vitro. Mechanistically, the TPR domain of UTX plays a critical role in regulating SG disassembly by interacting with G3BP1, the central hub of SG, to disrupt the scaffold network of SG under endoplasmic reticulum stress. Importantly, a clinical UTX mutation, D336G in TPR domain, increases cytoplasmic location of UTX, and stabilizes SG. While UTX ^D336G promotes, WT UTX or UTX ^TPR inhibits, cell growth and tumorigenesis by regulating SGs both in vitro and in nude mice, and such regulation is G3BP1 dependent. Together, the results suggest a novel cytoplasmic function of UTX as a negative regulator of SG homeostasis, which is involved in stress and disease states such as tumorigenesis.

Acute kidney injury (AKI) has high incidence and mortality rates. Present treatments are mostly symptomatic and cause side effects due to systemic distribution; thus, targeted kidney drug delivery is desired. Transmembrane kidney injury molecule-1 (KIM1) is expressed at low levels in normal kidneys but markedly up-regulated following injury, making it an ideal marker/target for injured kidneys. Here, assisted by AlphaFold, we constructed a library of 1885 peptides that target the extracellular Ig V domain of KIM1 based on interacting fragments from 47 potential KIM1 binding proteins followed by systemic optimization according to their binding energies with KIM1. Experimental validation of top candidates (TKP 1-5) demonstrated that TKP 4 efficiently targeted injured renal cells/kidneys, with its specificity demonstrated in KIM1 knockout cells/mice. TKP 4–decorating liposomes were loaded with nystatin, a renal-protective compound with systemic side effects, and efficiently targeted injured mouse kidneys and alleviated AKI. This work establishes a virtual platform to screen/identify drug delivery candidates with broad research/therapeutic potentials.

Obesity is a leading risk factor for development of hepatocellular carcinoma (HCC). High‐fat intake produces cytotoxic effects in liver cells, such as excessive reactive oxygen species (ROS) accumulation and apoptosis. How HCC cells regulate ROS level and escape the cytotoxic effects of high fat diet (HFD) stress remains unclear. Herein, this work reports a critical anti‐ROS/apoptotic role of the ubiquitin‐like protein interferon stimulated gene 15 (ISG15) in HFD‐promoted HCC. In mouse models and clinical HCC samples, upregulation of ISG15 is associated with hepatic steatosis. Notably, upregulated ISG15 elevates cellular glutathione levels, which subsequently reduces ROS accumulation and confers resistance to apoptosis in HCC cells. In diethylnitrosamine‐induced HCC mouse model, HFD‐feeding promotes HCC progression in wildtype mice, while tumor growth is significantly suppressed accompanied by apoptosis of HCC cells in Isg15‐KO mice. Mechanistically, ISG15 promotes the activity of γ‐glutamate cysteine ligase (γ‐GCL), a rate‐limiting heterodimeric holoenzyme of glutathione synthesis consisting of glutamate‐cysteine ligase catalytic subunit (GCLC) and glutamate‐cysteine ligase modifier subunit (GCLM). Independent of ISGylation, ISG15 forms an ISG15/GCLM/GCLC complex that promotes GCLM‐GCLC interaction, increases glutathione generation and inhibits HFD‐induced apoptosis in HCC cells. Together, an anti‐apoptotic ISG15‐γ‐GCL‐glutothione axis is suggested in HFD‐promoted HCC.

Upon genotoxic stresses, cells employ various DNA damage responses (DDRs), including DNA damage repair or apoptosis, to safeguard genome integrity. However, the determinants among different DDRs choices are largely unknown. Here, we report angiopoietin-like protein 8 (ANGPTL8), a secreted regulator of lipid metabolism, localizes to the nucleus and acts as a dynamic switch that directs DDRs towards apoptosis rather than DNA repair after genotoxin exposure. ANGPTL8 deficiency alleviates DNA damage and apoptosis in cells exposed to genotoxins, as well as in the liver or kidney of mice injured by hepatic ischemia/reperfusion or cisplatin treatment. Mechanistically, ANGPTL8 physically interacts with Poly (ADP-ribose) polymerase 1 (PARP1), in a PARylation-independent manner, and reduces the fluidity of PARP1-DNA condensates, thereby enhancing the pro-apoptotic accumulation of PARP1 and PAR chains on DNA lesions. However, the transcription of ANGPTL8 is gradually decreased following genotoxin treatment, partly due to downregulation of CCAAT enhancer binding protein alpha (CEBPA), presumably to avoid further cytotoxicity. Together, we provide new insights by which genotoxic stress induced DDRs are channeled to suicidal apoptosis to safeguard genome integrity.

Muscular atrophy accompanied by neuromuscular junction (NMJ) denervation is often observed after long-term chronic diseases and aging and is associated with substantial morbidity and mortality. Here, we report that histone methyltransferase G9a is elevated in the muscle of muscular atrophy model mice and that muscle-specific deficiency of G9a (Ehmt2^Ckmm−KO) alleviates muscular atrophy in both aged and denervated mice. Moreover, increased nerve-to-myofiber ratios and increased Agrin-Lrp4-MuSK signaling, which maintains NMJ, are found in aged Ehmt2^Ckmm−KO mice. Together, these data suggest that G9a promotes muscular atrophy and disrupts NMJ; thus, inhibiting the G9a level may be a potential therapy for muscular atrophy.

Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB) are neurodegenerative disorders characterized by the accumulation of α-synuclein aggregates. α-synuclein forms droplets via liquid-liquid phase separation (LLPS), followed by liquid-solid phase separation (LSPS) to form amyloids, how this process is physiologically-regulated remains unclear. β-synuclein colocalizes with α-synuclein in presynaptic terminals. Here, we report that β-synuclein partitions into α-synuclein condensates promotes the LLPS, and slows down LSPS of α-synuclein, while disease-associated β-synuclein mutations lose these capacities. Exogenous β-synuclein improves the movement defects and prolongs the lifespan of an α-synuclein-expressing NL5901 Caenorhabditis elegans strain, while disease-associated β-synuclein mutants aggravate the symptoms. Decapeptides targeted at the α-/β-synuclein interaction sites are rationally designed, which suppress the LSPS of α-synuclein, rescue the movement defects, and prolong the lifespan of C. elegans NL5901. Together, we unveil a Yin-Yang balance between α- and β-synuclein underlying the normal and disease states of PD and DLB with therapeutical potentials.

Acute kidney injury (AKI) exhibits high morbidity and mortality. Kidney injury molecule-1 (KIM1) is dramatically upregulated in renal tubules upon injury, and acts as a biomarker for various renal diseases. However, the exact role and underlying mechanism of KIM1 in the progression of AKI remain elusive. Herein, we report that renal tubular specific knockout ofKim1attenuates cisplatin- or ischemia/reperfusion-induced AKI in male mice. Mechanistically, transcription factor Yin Yang 1 (YY1), which is downregulated upon AKI, binds to the promoter ofKIM1and represses its expression. Injury-induced KIM1 binds to the ECD domain of death receptor 5 (DR5), which activates DR5 and the following caspase cascade by promoting its multimerization, thus induces renal cell apoptosis and exacerbates AKI. Blocking the KIM1-DR5 interaction with rationally designed peptides exhibit reno-protective effects against AKI. Here, we reveal a YY1-KIM1-DR5 axis in the progression of AKI, which warrants future exploration as therapeutic targets.

Adipose-tissue is a central metabolic organ for whole-body energy homeostasis. Here, we find that highly expressed H1.2, a linker histone variant, senses thermogenic stimuli in beige and brown adipocytes. Adipocyte H1.2 regulates thermogenic genes in inguinal white-adipose-tissue (iWAT) and affects energy expenditure. Adipocyte H1.2 deletion (H1.2AKO) male mice show promoted iWAT browning and improved cold tolerance; while overexpressing H1.2 shows opposite effects. Mechanistically, H1.2 binds to the promoter of Il10rα, which encodes an Il10 receptor, and positively regulates its expression to suppress thermogenesis in a beige cell autonomous manner. Il10rα overexpression in iWAT negates cold-enhanced browning of H1.2AKO male mice. Increased H1.2 level is also found in WAT of obese humans and male mice. H1.2AKO male mice show alleviated fat accumulation and glucose intolerance in long-term normal chow-fed and high fat diet-fed conditions; while Il10rα overexpression abolishes these effects. Here, we show a metabolic function of H1.2-Il10rα axis in iWAT.