Depletion of Prmt1 in Adipocytes Impairs Glucose Homeostasis in Diet-Induced Obesity

Regulation of hepatic lipogenesis by asymmetric arginine methylation

BACKGROUND AND AIMS

Hepatic lipogenesis is elevated in nutrient abundant conditions to convert the excess carbohydrate into triacylglycerol (TAG). Fatty acyl moiety of TAG is eventually transported into adipose tissues by very low density lipoprotein, leading to the accumulation of TAG as a preferred storage form of excess energy. Disruption of the balance between TAG clearance and synthesis leads to the accumulation of lipids in the liver, leading to the progression of non-alcoholic fatty liver disease (NAFLD) including non-alcoholic steatohepatitis. Protein arginine methyltransferase (PRMT) 6 has been linked to the various metabolic processes including hepatic gluconeogenesis, muscle atrophy and lipodystrophy in mouse models. However, the role of PRMT6 in the control of hepatic lipogenesis has not been elucidated to date.

METHODS

We assessed the interaction between PRMT6 and LXR alpha by using co-immunoprecipitation assay. The specific arginine residue of LXR alpha that is methylated by PRMT6 was assessed by LC-MS/MS assay and the functional consequences of LXR alpha methylation was explored by mSREBP-1c luciferase assay. The effect of PRMT6 on hepatic lipogenesis was assessed by adenovirus-mediated ectopic expression of PRMT6 or knockdown of PRMT6 via shRNA in hepatocytes. Finally, the role of PRMT6 in hepatic lipid metabolism in vivo was explored by either ectopic expression of LXR alpha mutant that is defective in PRMT6-mediated arginine methylation or knockdown of PRMT6 in liver.

RESULTS

We found that promoter activity of sterol regulatory element binding protein (SREBP) 1c is robustly activated by PRMT6. Interestingly, we demonstrated that PRMT6 binds to LXR alpha, a transcription factor for SREBP-1c, via its LXXLL motif, leading to the asymmetric dimethylation of an arginine residue and activation of this protein. Indeed, ectopic expression of PRMT6 in hepatocytes led to the enhanced expression of LXR alpha target genes in the lipogenic pathway. Conversely, genetic or pharmacological inhibition of PRMT6 diminished expression of lipogenic genes and the lipid accumulation in primary hepatocytes. Mechanistically, we found that asymmetric dimethylation of LXR alpha led to the dissociation of small heterodimer partner (SHP), a transcriptional co-inhibitor of this factor, resulting in the activation of LXR alpha-mediated transcriptional process. Finally, we showed that disruption of asymmetric dimethylation of LXR alpha in the liver led to the diminished expression of genes in the lipogenesis, resulting in the reduced hepatic lipid accumulation in high fat diet-fed mice in vivo.

CONCLUSIONS

We showed that PRMT6 modulates LXR alpha activity by conferring asymmetric dimethylation of arginine 253, thus blocking SHP-mediated inhibition and promoting hepatic lipid accumulation. These results suggest that PRMT6 is critical in the control of lipid homeostasis by regulation of LXR alpha-mediated lipogenesis in the liver.

Regulation of adipogenesis by histone methyltransferases

Epigenetic regulation is a critical component of lineage determination. Adipogenesis is the process through which uncommitted stem cells or adipogenic precursor cells differentiate into adipocytes, the most abundant cell type of the adipose tissue. Studies examining chromatin modification during adipogenesis have provided further understanding of the molecular blueprint that controls the onset of adipogenic differentiation. Unlike histone acetylation, histone methylation has context dependent effects on the activity of a transcribed region of DNA, with individual or combined marks on different histone residues providing distinct signals for gene expression. Over half of the 42 histone methyltransferases identified in mammalian cells have been investigated in their role during adipogenesis, but across the large body of literature available, there is a lack of clarity over potential correlations or emerging patterns among the different players. In this review, we will summarize important findings from studies published in the past 15 years that have investigated the role of histone methyltransferases during adipogenesis, including both protein arginine methyltransferases (PRMTs) and lysine methyltransferases (KMTs). We further reveal that PRMT1/4/5, H3K4 KMTs (MLL1, MLL3, MLL4, SMYD2 and SET7/9) and H3K27 KMTs (EZH2) all play positive roles during adipogenesis, while PRMT6/7 and H3K9 KMTs (G9a, SUV39H1, SUV39H2, and SETDB1) play negative roles during adipogenesis.

PRMT1 in human neoplasm: cancer biology and potential therapeutic target

Protein arginine methyltransferase 1 (PRMT1), the predominant type I protein arginine methyltransferase, plays a crucial role in normal biological functions by catalyzing the methylation of arginine side chains, specifically monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), within proteins. Recent investigations have unveiled an association between dysregulated PRMT1 expression and the initiation and progression of tumors, significantly impacting patient prognosis, attributed to PRMT1's involvement in regulating various facets of tumor cell biology, including DNA damage repair, transcriptional and translational regulation, as well as signal transduction. In this review, we present an overview of recent advancements in PRMT1 research across different tumor types, with a specific focus on its contributions to tumor cell proliferation, metastasis, invasion, and drug resistance. Additionally, we expound on the dynamic functions of PRMT1 during distinct stages of cancer progression, elucidating its unique regulatory mechanisms within the same signaling pathway and distinguishing between its promotive and inhibitory effects. Importantly, we sought to provide a comprehensive summary and analysis of recent research progress on PRMT1 in tumors, contributing to a deeper understanding of its role in tumorigenesis, development, and potential treatment strategies.

Cord blood DNA methylation of immune and lipid metabolism genes is associated with maternal triglycerides and child adiposity

OBJECTIVE

Fetal exposures may impact offspring epigenetic signatures and adiposity. The authors hypothesized that maternal metabolic traits associate with cord blood DNA methylation, which, in turn, associates with child adiposity.

METHODS

Fasting serum was obtained in 588 pregnant women (27-34 weeks' gestation), and insulin, glucose, high-density lipoprotein cholesterol, triglycerides, and free fatty acids were measured. Cord blood DNA methylation and child adiposity were measured at birth, 4-6 months, and 4-6 years. The association of maternal metabolic traits with DNA methylation (429,246 CpGs) for differentially methylated probes (DMPs) and regions (DMRs) was tested. The association of the first principal component of each DMR with child adiposity was tested, and mediation analysis was performed.

RESULTS

Maternal triglycerides were associated with the most DMPs and DMRs of all traits tested (261 and 198, respectively, false discovery rate < 0.05). DMRs were near genes involved in immune function and lipid metabolism. Triglyceride-associated CpGs were associated with child adiposity at 4-6 months (32 CpGs) and 4-6 years (2 CpGs). One, near CD226, was observed at both timepoints, mediating 10% and 22% of the relationship between maternal triglycerides and child adiposity at 4-6 months and 4-6 years, respectively.

CONCLUSIONS

DNA methylation may play a role in the association of maternal triglycerides and child adiposity.

Identification of adipose tissue transcriptomic memory of anorexia nervosa

BACKGROUND

Anorexia nervosa (AN) is a complex debilitating disease characterized by intense fear of weight gain and excessive exercise. It is the deadliest of any psychiatric disorder with a high rate of recidivism, yet its pathophysiology is unclear. The Activity-Based Anorexia (ABA) paradigm is a widely accepted mouse model of AN that recapitulates hypophagia and hyperactivity despite reduced body weight, however, not the chronicity.

METHODS

Here, we modified the prototypical ABA paradigm to increase the time to lose 25% of baseline body weight from less than 7 days to more than 2 weeks. We used this paradigm to identify persistently altered genes after weight restoration that represent a transcriptomic memory of under-nutrition and may contribute to AN relapse using RNA sequencing. We focused on adipose tissue as it was identified as a major location of transcriptomic memory of over-nutririon.

RESULTS

We identified 300 dysregulated genes that were refractory to weight restroration after ABA, including Calm2 and Vps13d, which could be potential global regulators of transcriptomic memory in both chronic over- and under-nutrition.

CONCLUSION

We demonstrated the presence of peristent changes in the adipose tissue transcriptome in the ABA mice after weight restoration. Despite being on the opposite spectrum of weight perturbations, majority of the transcriptomic memory genes of under- and over-nutrition did not overlap, suggestive of the different mechanisms involved in these extreme nutritional statuses.

Impaired BCAA catabolism in adipose tissues promotes age-associated metabolic derangement

Adipose tissues are central in controlling metabolic homeostasis and failure in their preservation is associated with age-related metabolic disorders. The exact role of mature adipocytes in this phenomenon remains elusive. Here we describe the role of adipose branched-chain amino acid (BCAA) catabolism in this process. We found that adipocyte-specific Crtc2 knockout protected mice from age-associated metabolic decline. Multiomics analysis revealed that BCAA catabolism was impaired in aged visceral adipose tissues, leading to the activation of mechanistic target of rapamycin complex (mTORC1) signaling and the resultant cellular senescence, which was restored by Crtc2 knockout in adipocytes. Using single-cell RNA sequencing analysis, we found that age-associated decline in adipogenic potential of visceral adipose tissues was reinstated by Crtc2 knockout, via the reduction of BCAA-mTORC1 senescence-associated secretory phenotype axis. Collectively, we propose that perturbation of BCAA catabolism by CRTC2 is critical in instigating age-associated remodeling of adipose tissue and the resultant metabolic decline in vivo.

Involvement of a novel cAMP signaling mediator for beige adipogenesis

BACKGROUND

Exposure to cold temperature stimulates the sympathetic nervous system that activates β-adrenergic receptor signals in brown and beige adipocytes, leading to the induction of adaptive thermogenesis in mammals. Prominin-1 (PROM1) is a pentaspan transmembrane protein that is widely identified as a marker for stem cells, although the role of this protein as a regulator of many intracellular signaling cascades has been recently delineated. The main focus of the current study is to identify the previously unknown role of PROM1 in beige adipogenesis and adaptive thermogenesis.

METHODS

Prom1 whole body knockout (Prom1 KO) mice, Prom1 adipogenic progenitor (AP) cell-specific knockout (Prom1 APKO) mice and Prom1 adipocyte-specific knockout (Prom1 AKO) mice were constructed and were subject for the induction of adaptive thermogenesis. The effect of systemic Prom1 depletion was evaluated by hematoxylin and eosin staining, immunostaining, and biochemical analysis in vivo. Flow cytometric analysis was performed to determine the identity of PROM1-expressing cell types, and the resultant cells were subject to beige adipogenesis in vitro. The potential role of PROM1 and ERM in cAMP signaling was also assessed in undifferentiated AP cells in vitro. Finally, the specific effect of Prom1 depletion on AP cell or mature adipocytes on adaptive thermogenesis was evaluated by hematoxylin and eosin staining, immunostaining, and biochemical analysis in vivo.

RESULTS

Prom1 KO mice displayed an impairment in cold- or β3-adrenergic agonist-induced adaptive thermogenesis in subcutaneous adipose tissues (SAT) but not in brown adipose tissues (BAT). By fluorescence-activated cell sorting (FACS) analysis, we identified that PROM1 positive cells are enriched in PDGFRα⁺Sca1⁺ AP cells from SAT. Interestingly, Prom1 knockout stromal vascular fractions showed reduced PDGFRα expression, suggesting a role of PROM1 in beige adipogenic potential. Indeed, we found that Prom1-deficient AP cells from SAT showed reduced potential for beige adipogenesis. Furthermore, AP cell-specific depletion of Prom1, but not adipocyte-specific depletion of Prom1, displayed defects in adaptive thermogenesis as evidenced by resistance to cold-induced browning of SAT and dampened energy expenditure in mice.

CONCLUSION

We found that PROM1 positive AP cells are essential for the adaptive thermogenesis by ensuing stress-induced beige adipogenesis. Identification of PROM1 ligand might be useful in the activation of thermogenesis that could be potentially beneficial in combating obesity.

Protein arginine methyltransferase PRMT1 promotes adipogenesis by modulating transcription factors C/EBPβ and PPARγ

Protein arginine methyltransferase 1 (PRMT1) methylates a variety of histone and nonhistone protein substrates to regulate multiple cellular functions such as transcription, DNA damage response, and signal transduction. It has been reported as an emerging regulator of various metabolic pathways including glucose metabolism in the liver, atrophy in the skeletal muscle, and lipid catabolism in the adipose tissue. However, the underlying mechanisms governing how PRMT1 regulates adipogenesis remain elusive. Here, we delineate the roles of PRMT1 in mitotic clonal expansion and adipocyte differentiation. Gain and loss of functions demonstrate that PRMT1 is essential for adipogenesis of 3T3-L1 and C3H10T1/2 cells. Mechanistically, we show PRMT1 promotes the expression of transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) by catalyzing histone modification H4R3me2a and impedes the activation of Wnt/β-catenin signaling by increasing the level of Axin to accelerate adipogenic differentiation. In addition, we demonstrate mitotic clonal expansion is suppressed by PRMT1 deficiency. PRMT1 interacts with transcription factor CCATT enhancer-binding protein β (C/EBPβ), and the absence of PRMT1 leads to the depressed phosphorylation of C/EBPβ. Interestingly, we discover PRMT1 acts as a positive regulator of C/EBPβ protein stability through decreasing the level of E3 ubiquitin ligase Smurf2, which promotes the ubiquitination and degradation of C/EBPβ, thus facilitating adipogenesis. Collectively, these discoveries highlight a critical role of PRMT1 in adipogenesis and provide potential therapeutic targets for the treatment of obesity.

Sperm Histone H3 Lysine 4 tri-methylation serves as a metabolic sensor of paternal obesity and is associated with the inheritance of metabolic dysfunction

Objective

Parental environmental exposures can strongly influence descendant risks for adult disease. How paternal obesity changes the sperm chromatin leading to the acquisition of metabolic disease in offspring remains controversial and ill-defined. The objective of this study was to assess (1) whether obesity induced by a high-fat diet alters sperm histone methylation; (2) whether paternal obesity can induce metabolic disturbances across generations; (3) whether there could be cumulative damage to the sperm epigenome leading to enhanced metabolic dysfunction in descendants; and (4) whether obesity-sensitive regions associate with embryonic epigenetic and transcriptomic profiles. Using a genetic mouse model of epigenetic inheritance, we investigated the role of histone H3 lysine 4 methylation (H3K4me3) in the paternal transmission of metabolic dysfunction. This transgenic mouse overexpresses the histone demethylase enzyme KDM1A in the developing germline and has an altered sperm epigenome at the level of histone H3K4 methylation. We hypothesized that challenging transgenic sires with a high-fat diet would further erode the sperm epigenome and lead to enhanced metabolic disturbances in the next generations.

Methods

To assess whether paternal obesity can have inter- or transgenerational impacts, and if so to identify potential mechanisms of this non-genetic inheritance, we used wild-type C57BL/6NCrl and transgenic males with a pre-existing altered sperm epigenome. To induce obesity, sires were fed either a control or high-fat diet (10% or 60% kcal fat, respectively) for 10–12 weeks, then bred to wild-type C57BL/6NCrl females fed a regular diet. F₁ and F₂ descendants were characterized for metabolic phenotypes by examining the effects of paternal obesity by sex, on body weight, fat mass distribution, the liver transcriptome, intraperitoneal glucose, and insulin tolerance tests. To determine whether obesity altered the F₀ sperm chromatin, native chromatin immunoprecipitation-sequencing targeting H3K4me3 was performed. To gain insight into mechanisms of paternal transmission, we compared our sperm H3K4me3 profiles with embryonic and placental chromatin states, histone modification, and gene expression profiles.

Results

Obesity-induced alterations in H3K4me3 occurred in genes implicated in metabolic, inflammatory, and developmental processes. These processes were associated with offspring metabolic dysfunction and corresponded to genes enriched for H3K4me3 in embryos and overlapped embryonic and placenta gene expression profiles. Transgenerational susceptibility to metabolic disease was only observed when obese F₀ had a pre-existing modified sperm epigenome. This coincided with increased H3K4me3 alterations in sperm and more severe phenotypes affecting their offspring.

Conclusions

Our data suggest sperm H3K4me3 might serve as a metabolic sensor that connects paternal diet with offspring phenotypes via the placenta. This non-DNA-based knowledge of inheritance has the potential to improve our understanding of how environment shapes heritability and may lead to novel routes for the prevention of disease. This study highlights the need to further study the connection between the sperm epigenome, placental development, and children's health.

Summary sentence

Paternal obesity impacts sperm H3K4me3 and is associated with placenta, embryonic and metabolic outcomes in descendants.

•

Sperm H3K4me3 serves as a metabolic sensor of HFD-induced obesity.

•

Obesity-altered sperm H3K4me3 corresponds to embryonic transcription and chromatin profiles.

•

HFD- and KDM1A-induced cumulative sperm epimutations enhanced F₁ metabolic dysfunction.

•

Sperm epimutations may influence placenta function inducing F₁ metabolic phenotypes.