An antioxidant feedforward cycle coordinated by linker histone variant H1.2 and NRF2 that drives nonsmall cell lung cancer progression.

Nonsmall cell lung cancer (NSCLC) is highly malignant with limited treatment options, platinum-based chemotherapy is a standard treatment for NSCLC with resistance commonly seen. NSCLC cells exploit enhanced antioxidant defense system to counteract excessive reactive oxygen species (ROS), which contributes largely to tumor progression and resistance to chemotherapy, yet the mechanisms are not fully understood. Recent studies have suggested the involvement of histones in tumor progression and cellular antioxidant response; however, whether a major histone variant H1.2 (H1C) plays roles in the development of NSCLC remains unclear. Herein, we demonstrated that H1.2 was increasingly expressed in NSCLC tumors, and its expression was correlated with worse survival. When crossing the H1c knockout allele with a mouse NSCLC model (KrasLSL-G12D/+), H1.2 deletion suppressed NSCLC progression and enhanced oxidative stress and significantly decreased the levels of key antioxidant glutathione (GSH) and GCLC, the catalytic subunit of rate-limiting enzyme for GSH synthesis. Moreover, high H1.2 was correlated with the IC50 of multiple chemotherapeutic drugs and with worse prognosis in NSCLC patients receiving chemotherapy; H1.2-deficient NSCLC cells presented reduced survival and increased ROS levels upon cisplatin treatment, while ROS scavenger eliminated the survival inhibition. Mechanistically, H1.2 interacted with NRF2, a master regulator of antioxidative response; H1.2 enhanced the nuclear level and stability of NRF2 and, thus, promoted NRF2 binding to GCLC promoter and the consequent transcription; while NRF2 also transcriptionally up-regulated H1.2. Collectively, these results uncovered a tumor-driving role of H1.2 in NSCLC and indicate an "H1.2-NRF2" antioxidant feedforward cycle that promotes tumor progression and chemoresistance.

Loss of renal tubular G9a benefits acute kidney injury by lowering focal lipid accumulation via CES1.

Surgery-induced renal ischemia and reperfusion (I/R) injury and nephrotoxic drugs like cisplatin can cause acute kidney injury (AKI), for which there is no effective therapy. Lipid accumulation is evident following AKI in renal tubules although the mechanisms and pathological effects are unclear. Here, we report that Ehmt2-encoded histone methyltransferase G9a is upregulated in patients and mouse kidneys after AKI. Renal tubular specific knockout of G9a (Ehmt2Ksp ) or pharmacological inhibition of G9a alleviates lipid accumulation associated with AKI. Mechanistically, G9a suppresses transcription of the lipolytic enzyme Ces1; moreover, G9a and farnesoid X receptor (FXR) competitively bind to the same promoter regions of Ces1. Ces1 is consistently observed to be downregulated in the kidney of AKI patients. Pharmacological inhibition of Ces1 increases lipid accumulation, exacerbates renal I/R-injury and eliminates the beneficial effects on AKI observed in Ehmt2Ksp mice. Furthermore, lipid-lowering atorvastatin and an FXR agonist alleviate AKI by activating Ces1 and reducing renal lipid accumulation. Together, our results reveal a G9a/FXR-Ces1 axis that affects the AKI outcome via regulating renal lipid accumulation.

Histone H1.2 promotes hepatocarcinogenesis by regulating signal transducer and activator of transcription 3 signaling.

Linker histone H1.2 (H1.2), encoded by HIST1H1C (H1C), is a major H1 variant in somatic cells. Among five histone H1 somatic variants, upregulated H1.2 was found in human hepatocellular carcinoma (HCC) samples and in a diethylnitrosamine (DEN)-induced HCC mouse model. In vitro, H1.2 overexpression accelerated proliferation of HCC cell lines, whereas H1.2 knockdown (KD) had the opposite effect. In vivo, H1.2 insufficiency or deficiency (H1c KD or H1c KO) alleviated inflammatory response and HCC development in DEN-treated mice. Mechanistically, H1.2 regulated the activation of signal transducer and activator of transcription 3 (STAT3), which in turn positively regulated H1.2 expression by binding to its promoter. Moreover, upregulation of the H1.2/STAT3 axis was observed in human HCC samples, and was confirmed in mouse models of methionine-choline-deficient diet induced nonalcoholic steatohepatitis or lipopolysaccharide induced acute inflammatory liver injury. Disrupting this feed-forward loop by KD of STAT3 or treatment with STAT3 inhibitors rescued H1.2 overexpression-induced proliferation. Moreover, STAT3 inhibitor treatment-ameliorated H1.2 overexpression promoted xenograft tumor growth. Therefore, H1.2 plays a novel role in inflammatory response by regulating STAT3 activation in HCC, thus, blockade of the H1.2/STAT3 loop is a potential strategy against HCC.

Lmo4-resistin signaling contributes to adipose tissue-liver crosstalk upon weight cycling.

Repeated cycles of weight loss and regain, known as weight cycling, is often seen when people try to lose weight. The exact pathophysiological effects and the underlying mechanisms of weight cycling remain largely unclear. Here, we report that weight cycling induced by alternating feeding mice with a low-fat diet or a high-fat diet in a 1-week switch protocol caused further increased epididymal white adipose tissue (eWAT) weight, preadipocyte proliferation, hepatic inflammation, fasting blood glucose level, and glucose intolerance, compared with the continuously HF-fed mice. Combining the secretory protein database with RNA-sequencing and quantitative PCR (qPCR) results in eWAT, the mRNA levels of several adipokines, including Retn (encoding resistin), were found altered by weight cycling. A transcriptional co-factor Lmo4 was found regulated by weight cycling; Lmo4 enhanced preadipocyte proliferation, in vitro adipogenesis, transcription of Retn, and resistin secretion in 3T3-L1 cells. Primary mouse hepatocytes administrated with recombinant mouse resistin (rm-resistin), or exposed to media from Lmo4-overexpressed 3T3-L1 cells, showed increased inflammatory responses and gluconeogenesis. Furthermore, rm-resistin-injected normal chow-fed mice showed upregulated blood glucose level by increasing gluconeogenesis, and upregulated the hepatic inflammatory responses. Together, our results suggest a regulatory role of Lmo4-resistin signaling in weight cycling, indicating a crosstalk between the adipose tissue and liver.

Histone demethylase UTX is a therapeutic target for diabetic kidney disease.

KEY POINTS: Diabetic kidney disease (DKD) is a major complication of diabetes. We found that UTX (ubiquitously transcribed tetratricopeptide repeat on chromosome X, also known as KDM6A), a histone demethylase, was upregulated in the renal mesangial and tubular cells of diabetic mice and DKD patients. In cultured renal mesangial and tubular cells, UTX overexpression promoted palmitic acid-induced elevation of inflammation and DNA damage, whereas UTX knockdown or GSK-J4 treatment showed the opposite effects. We found that UTX demethylase activity-dependently regulated the transcription of inflammatory genes and apoptosis; moreover, UTX bound with p53 and p53-dependently exacerbated DNA damage. Administration of GSK-J4, an H3K27 demethylase inhibitor, ameliorated the diabetes-induced renal abnormalities in db/db mice, an animal model of type 2 diabetes. These results revealed the possible mechanisms underlying the regulation of histone methylation in DKD and suggest UTX as a potential therapeutic target for DKD. ABSTRACT: Diabetic kidney disease (DKD) is a microvascular complication of diabetes and the leading cause of end-stage kidney disease worldwide without effective therapy available. UTX (ubiquitously transcribed tetratricopeptide repeat on chromosome X, also known as KDM6A), a histone demethylase that removes the di- and tri-methyl groups from histone H3K27, plays important biological roles in gene activation, cell fate control and life span regulation in Caenorhabditis elegans. In the present study, we report upregulated UTX in the kidneys of diabetic mice and DKD patients. Administration of GSK-J4, an H3K27 demethylase inhibitor, ameliorated the diabetes-induced renal dysfunction, abnormal morphology, inflammation, apoptosis and DNA damage in db/db mice, comprising an animal model of type 2 diabetes. In cultured renal mesanglial and tubular cells, UTX overexpression promoted palmitic acid induced elevation of inflammation and DNA damage, whereas UTX knockdown or GSK-J4 treatment showed the opposite effects. Mechanistically, we found that UTX demethylase activity-dependently regulated the transcription of inflammatory genes; moreover, UTX bound with p53 and p53-dependently exacerbated DNA damage. Collectively, our results suggest UTX as a potential therapeutic target for DKD.

Histone methyltransferase G9a modulates hepatic insulin signaling via regulating HMGA1.

Hepatic insulin sensitivity is critical for glucose homeostasis, and insulin resistance is a fundamental syndrome found in various metabolic disorders, including obesity and type 2 diabetes. Despite considerable studies on the mechanisms of hepatic insulin resistance, the link between epigenetic regulation and the development of insulin resistance remains elusive. Here, we reported that G9a/EHMT2, a histone methyltransferase, was markedly decreased in the liver of db/db mice and high-fat diet (HFD)-fed mice. In cultured hepatic cells, G9a knockdown resulted in downregulation of insulin receptor, p-AKT and p-GSK3ß; while upon upregulation, G9a prevented the palmitic acid- or glucosamine-induced insulin resistance by preserving the normal level of insulin receptor and integrity of insulin signaling. Further mechanistic study suggested that G9a regulated the expression level of high mobility group AT-hook 1 (HMGA1), a key regulator responsible for the transcription of insulin receptor (INSR) gene. Overexpression of HMGA1 normalized the impaired insulin signaling in G9a knockdown hepatic cells. Importantly, in db/db mice, restoring the expression level of G9a not only upregulated HMGA1 level and improved the impaired hepatic insulin signaling, but also alleviated hyperglycemia and hyperinsulinemia. Together, our results revealed a novel role for G9a in modulating insulin signaling, at least in part, depending on its regulatory function on HMGA1.

Tet1 deficiency exacerbates oxidative stress in acute kidney injury by regulating superoxide dismutase.

Rationale: Increased methylation of key genes has been observed in kidney diseases, suggesting that the ten-eleven translocation (Tet) methyl-cytosine dioxygenase family as well as 5mC oxidation may play important roles. As a member of the Tet family, the role of Tet1 in acute kidney injury (AKI) remains unclear. Methods: Tet1 knockout mice, with or without tempol treatment, a scavenger of reactive oxygen species (ROS), were challenged with ischemia and reperfusion (I/R) injury or unilateral ureteral obstruction (UUO) injury. RNA-sequencing, Western blotting, qRT-PCR, bisulfite sequencing, chromatin immunoprecipitation, immunohistochemical staining, and dot blot assays were performed. Results: Tet1 expression was rapidly upregulated following I/R or UUO injury. Moreover, Tet1 knockout mice showed increased renal injury and renal cell death, increased ROS accumulation, G2/M cell cycle arrest, inflammation, and fibrosis. Severe renal damage in injured Tet1 knockout mice was alleviated by tempol treatment. Mechanistically, Tet1 reduced the 5mC levels in an enzymatic activity-dependent manner on the promoters of Sod1 and Sod2 to promote their expression, thus lowering injury-induced excessive ROS and reducing I/R or UUO injury. Conclusions: Tet1 plays an important role in the development of AKI by promoting SOD expression through a DNA demethylase-dependent mechanism.

Linker histone variant H1.2 is a brake on white adipose tissue browning.

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.

Mecp2 protects kidney from ischemia-reperfusion injury through transcriptional repressing IL-6/STAT3 signaling.

Rationale: Ischemia-reperfusion (IR) induced acute kidney injury (AKI) causes serious clinical problems associated with high morbidity and mortality. Mecp2 is a methyl-CpG binding protein, its mutation or deletion causes a neurodevelopment disease called Rett syndrome. Notably, some Rett syndrome patients present urological dysfunctions. It remains unclear whether and how Mecp2 affects AKI. Methods: Renal tubular cell specific Mecp2 deletion mice challenged with IR injury were used to investigate the effects of Mecp2 on renal tubular damage, function, cell death, fibrosis and inflammation. Cultured renal epithelial cell lines were transfected with wildtype or different domain-deletion mutants of Mecp2 to study the effects of Mecp2 on Il-6/STAT3 signaling. Results: Our results indicated rapidly upregulated Mecp2 upon acute in vivo and in vitro renal injury. Notably, increased tubular MeCP2 staining was also found in the renal sections of AKI patients. Furthermore, ablation of Mecp2 aggravated renal injury, and promoted renal cell death, inflammation, and fibrosis. Mechanistically, through its transcriptional repression domain, Mecp2 bound to the promoter of proinflammatory cytokine Il-6 to negatively regulate its expression, thus inhibiting STAT3 activation. Conclusions: A novel protective role of Mecp2 against AKI via repressing the Il-6/STAT3 axis was suggested.

Vitamin C Inhibits the Metabolic Changes Induced by Tet1 Insufficiency Under High Fat Diet Stress.

SCOPE: DNA methylation contributes to obesity, but the role of the DNA demethylase ten-eleven translocation protein 1 (Tet1) in obesity remains unclear. Vitamin C is a cofactor for the Tet family of proteins, but whether vitamin C can be used to treat obesity via Tet1 awaits clarification. METHODS AND RESULTS: Tet1+/+ and Tet1+/- mice are fed a high fat diet (HFD). Higher weight gain and more severe hepatic steatosis, accompanied by reduced 5-hydromethylcytosine (5hmC) levels, are found in the white adipose tissue and liver of Tet1+/- mice. Accumulated lipids are observed in palmitic acid or oleic acid treated primary hepatocytes derived from Tet1+/- mice, which are rescued by Tet1 overexpression or vitamin C treatment. Bisulfite sequencing reveals higher DNA methylation levels on lipolysis related genes in the liver of Tet1+/- mice. Notably, oral intake of vitamin C normalizes DNA methylation levels, promotes lipolysis, and decreases obesity in HFD-fed Tet1+/- mice. CONCLUSIONS: The results reveal a novel function of Tet1 in obesity and provide a new mechanism for the beneficial role of vitamin C in metabolic diseases through enhanced Tet1 activity.

Muscular G9a Regulates Muscle-Liver-Fat Axis by Musclin Under Overnutrition in Female Mice.

Cross talk among different tissues and organs is a hotspot in metabolic research. Recent studies have revealed the regulatory roles of a number of myokines in metabolism. Here, we report that female mice lacking muscle-specific histone methylase G9a (Ehmt2 Ckmm knockout [KO] or Ehmt2 HSA KO) are resistant to high-fat diet (HFD)-induced obesity and hepatic steatosis. Furthermore, we identified a significantly upregulated circulating level of musclin, a myokine, in HFD-fed Ehmt2 Ckmm KO or Ehmt2 HSA KO female mice. Similarly, upregulated musclin was observed in mice injected with two structurally different inhibitors for G9a methylase activity: BIX01294 and A366. Moreover, injection of recombinant full-length musclin or its functional core domain inhibited the HFD-induced obesity and hepatic steatosis in wild-type female and male mice. Mechanistically, G9a methylase activity-dependently regulated muscular musclin level by binding to its promoter, also by regulating phosphorylated-FOXO1/FOXO1 levels in vivo and in vitro. Collectively, these data suggest a critical role for G9a in the muscle-liver-fat metabolic axis, at least for female mice. Musclin may serve as a potential therapeutic candidate for obesity and associated diseases.

Histone methyltransferase G9a protects against acute liver injury through GSTP1.

Acute liver injury is commonly caused by bacterial endotoxin/lipopolysaccharide (LPS), and by drug overdose such as acetaminophen (APAP). The exact role of epigenetic modification in acute liver injury remains elusive. Here, we investigated the role of histone methyltransferase G9a in LPS- or APAP overdose-induced acute liver injury. Under D-galactosamine sensitization, liver-specific G9a-deficient mice (L-G9a-/-) exhibited 100% mortality after LPS injection, while the control and L-G9a+/- littermates showed very mild mortality. Moreover, abrogation of hepatic G9a or inhibiting the methyltransferase activity of G9a aggravated LPS-induced liver damage. Similarly, under sublethal APAP overdose, L-G9a-/- mice displayed more severe liver injury. Mechanistically, ablation of G9a inhibited H3K9me1 levels at the promoters of Gstp1/2, two liver detoxifying enzymes, and consequently suppressed their transcription. Notably, treating L-G9a-/- mice with recombinant mouse GSTP1 reversed the LPS- or APAP overdose-induced liver damage. Taken together, we identify a novel beneficial role of G9a-GSTP1 axis in protecting against acute liver injury.

Fat-Specific Knockout of Mecp2 Upregulates Slpi to Reduce Obesity by Enhancing Browning.

Abnormalities of methyl-CpG binding protein 2 (Mecp2) cause neurological disorders with metabolic dysfunction; however, its role in adipose tissues remains unclear. Here, we report upregulated Mecp2 in white adipose tissues (WAT) of obese humans, as well as in obese mice and during in vitro adipogenesis. Normal chow-fed adipocyte-specific Mecp2 knockout mice (Mecp2 Adi KO mice) showed a lean phenotype, with downregulated lipogenic genes and upregulated thermogenic genes that were identified using RNA sequencing. Consistently, the deficiency of Mecp2 in adipocytes protected mice from high-fat diet (HFD)-induced obesity and inhibited in vitro adipogenesis. Furthermore, Mecp2 Adi KO mice showed increased browning under different stimuli, including cold treatment. Mechanistically, Mecp2 bound to the promoter of secretory leukocyte protease inhibitor (Slpi) and negatively regulated its expression. Knockdown of Slpi in inguinal WAT of Mecp2 Adi KO mice prevented cold-induced browning. Moreover, recombinant SLPI treatment reduced the HFD-induced obesity via enhancing browning. Together, our results suggest a novel non-central nervous system function of Mecp2 in obesity by suppressing browning, at least partially, through regulating adipokine Slpi.