SREBP1c-PARP1 axis tunes anti-senescence activity of adipocytes and ameliorates metabolic imbalance in obesity

DNA damage, obesity and obesity-related health complications: what are new data telling us?

PURPOSE OF REVIEW

Obesity is associated with increased DNA damage, which may in turn contribute to the development of obesity-related complications. DNA damage can also affect adipocyte biology, resulting in increased adiposity. Carefully managed weight loss programs can reverse this process. This article surveys new data that support these contentions.

RECENT FINDINGS

Whole exome sequencing analyses have identified rare variants linked to high BMI and adiposity. Two of the identified genes are linked to DNA damage and DNA repair, suggesting that DNA damage itself may play a role in the cause of obesity. It has also been recognized that obesity increases DNA damage in breast tissue of carriers of BRCA mutations and rates of tumour formation in BRCA1+ mice, indicating effect of obesity on cancer development in high-risk populations. In addition, obesity promotes cancer cell chemoresistance by decreasing fatty acid oxidation involved in cellular DNA damage response, leading to apoptotic cellular death. Obesity is also associated with a reduced capacity of oocytes to repair sperm DNA damage, leading to lower in-vitro fertilization rates in women with obesity.

SUMMARY

DNA damage and cellular responses to DNA damage can be both the result and the cause of obesity and can strongly influence the development and treatment of obesity-associated diseases.

SenNet recommendations for detecting senescent cells in different tissues

Once considered a tissue culture-specific phenomenon, cellular senescence has now been linked to various biological processes with both beneficial and detrimental roles in humans, rodents and other species. Much of our understanding of senescent cell biology still originates from tissue culture studies, where each cell in the culture is driven to an irreversible cell cycle arrest. By contrast, in tissues, these cells are relatively rare and difficult to characterize, and it is now established that fully differentiated, postmitotic cells can also acquire a senescence phenotype. The SenNet Biomarkers Working Group was formed to provide recommendations for the use of cellular senescence markers to identify and characterize senescent cells in tissues. Here, we provide recommendations for detecting senescent cells in different tissues based on a comprehensive analysis of existing literature reporting senescence markers in 14 tissues in mice and humans. We discuss some of the recent advances in detecting and characterizing cellular senescence, including molecular senescence signatures and morphological features, and the use of circulating markers. We aim for this work to be a valuable resource for both seasoned investigators in senescence-related studies and newcomers to the field.

Lipids and lipid metabolism in cellular senescence: Emerging targets for age-related diseases

Cellular senescence is a kind of cellular state triggered by endogenous or exogenous stimuli, which is mainly characterized by stable cell cycle arrest and complex senescence-associated secretory phenotype (SASP). Once senescent cells accumulate in tissues, they may eventually accelerate the progression of age-related diseases, such as atherosclerosis, osteoarthritis, chronic lung diseases, cancers, etc. Recent studies have shown that the disorders of lipid metabolism are not only related to age-related diseases, but also regulate the cellular senescence process. Based on existing research evidences, the changes in lipid metabolism in senescent cells are mainly concentrated in the metabolic processes of phospholipids, fatty acids and cholesterol. Obviously, the changes in lipid-metabolizing enzymes and proteins involved in these pathways play a critical role in senescence. However, the link between cellular senescence, changes in lipid metabolism and age-related disease remains to be elucidated. Herein, we summarize the lipid metabolism changes in senescent cells, especially the senescent cells that promote age-related diseases, as well as focusing on the role of lipid-related enzymes or proteins in senescence. Finally, we explore the prospect of lipids in cellular senescence and their potential as drug targets for preventing and delaying age-related diseases.

Gut microbiota-bile acid crosstalk and metabolic fatty liver in spotted seabass (Lateolabrax maculatus): The role of a cholesterol, taurine and glycine supplement

The prevalent practice of substituting fishmeal with plant protein frequently leads to disturbances in bile acid metabolism, subsequently increasing the incidence of metabolic liver diseases. Bile acid nutrients such as cholesterol, taurine and glycine have been shown to enhance bile acid synthesis and confer beneficial effects on growth. Therefore, this study aimed to investigate the effects of cholesterol-taurine-glycine (Ch-Tau-Gly) supplement on bile acid metabolism and liver health in spotted seabass (Lateolabrax maculatus) fed a plant-based diet. Two isonitrogenous and isolipidic diets were formulated: (1) plant protein-based diet (PP); (2) PP supplemented 0.5% cholesterol, 0.5% taurine and 1.3% glycine (CTG). Each experimental diet was randomly fed to quadruplicate groups of 30 feed-trained spotted seabass in each tank. The results revealed that supplementing plant-based diet with Ch-Tau-Gly supplement led to an increase in carcass ratio (meat yield) in spotted seabass (P < 0.05), indirectly contributing positively to their growth. The dietary supplement effectively suppressed endogenous cholesterol synthesis in the liver, promoted the expression of bile acid synthesis enzyme synthesis, and simultaneously the expression of intestinal fxr and its downstream genes, including hnf4α and shp (P < 0.05). The reduction in Lactobacillus_salivarius and bile salt hydrolase (BSH) were observed in CTG group with concurrently increased conjugated chenodeoxycholic acid (CDCA) bile acids (P < 0.05), suggesting the enhancement of the hydrophilicity of the bile acid pool. In CTG group, fatty liver was alleviated with a corresponding increase in lipid metabolism, characterized by a downregulation of genes associated with lipogenesis and lipid droplet deposition, along with an upregulation of genes related to lipolysis. Our study underscored the ability of Ch-Tau-Gly supplement to influence the gut microbiota, leading to an increase in the levels of conjugated CDCA (P < 0.05) in the bile acid pool of spotted seabass. The interplay between the gut microbiota and bile acids might constitute a crucial pathway in the promotion of liver health. These findings offer a promising solution, suggesting that Ch-Tau-Gly supplement have the potential to promote the growth of aquatic species and livestock fed on plant-based diets while addressing issues related to metabolic fatty liver.

M2 macrophage-derived TGF-β induces age-associated loss of adipogenesis through progenitor cell senescence

OBJECTIVES

Adipose tissue is an endocrine and energy storage organ composed of several different cell types, including mature adipocytes, stromal cells, endothelial cells, and a variety of immune cells. Adipose tissue aging contributes to the pathogenesis of metabolic dysfunction and is likely induced by crosstalk between adipose progenitor cells (APCs) and immune cells, but the underlying molecular mechanisms remain largely unknown. In this study, we revealed the biological role of p16high senescent APCs, and investigated the crosstalk between each cell type in the aged white adipose tissue.

METHODS

We performed the single-cell RNA sequencing (scRNA-seq) analysis on the p16high adipose cells sorted from aged p16-CreERT2/Rosa26-LSL-tdTomato mice. We also performed the time serial analysis on the age-dependent bulk RNA-seq datasets of human and mouse white adipose tissues to infer the transcriptome alteration of adipogenic potential within aging.

RESULTS

We show that M2 macrophage-derived TGF-β induces APCs senescence which impairs adipogenesis in vivo. p16high senescent APCs increase with age and show loss of adipogenic potential. The ligand-receptor interaction analysis reveals that M2 macrophages are the donors for TGF-β and the senescent APCs are the recipients. Indeed, treatment of APCs with TGF-β1 induces senescent phenotypes through mitochondrial ROS-mediated DNA damage in vitro. TGF-β1 injection into gonadal white adipose tissue (gWAT) suppresses adipogenic potential and induces fibrotic genes as well as p16 in APCs. A gWAT atrophy is observed in cancer cachexia by APCs senescence, whose induction appeared to be independent of TGF-β induction.

CONCLUSIONS

Our results suggest that M2 macrophage-derived TGF-β induces age-related lipodystrophy by APCs senescence. The TGF-β treatment induced DNA damage, mitochondrial ROS, and finally cellular senescence in APCs.

Tubular insulin-induced gene 1 deficiency promotes NAD+ consumption and exacerbates kidney fibrosis

Profibrotic proximal tubules (PT) were identified as a unique phenotype of proximal tubule cells (PTCs) in renal fibrosis by single-cell RNA sequencing (scRNA-seq). Controlling the process of renal fibrosis requires understanding how to manage the S1 subset's branch to the S3 subset rather than to the profibrotic PT subset. Insulin-induced gene 1 (Insig1) is one of the branch-dependent genes involved in controlling this process, although its role in renal fibrosis is unknown. Here, we discovered that tubular Insig1 deficiency, rather than fibroblast Insig1 deficiency, plays a detrimental role in the pathogenesis of renal fibrosis in vivo and in vitro. Overexpression of Insig1 profoundly inhibited renal fibrosis. Mechanistically, Insig1 deletion in PTCs boosted SREBP1 nuclear localization, increasing Aldh1a1 transcriptional activity, causing excessive NAD+ consumption and ER enlargement, as well as accelerating renal fibrosis. We also identified nicardipine as a selective inhibitor of Aldh1a1, which could restore NAD+ and maintain ER homeostasis, as well as improve renal fibrosis. Together, our findings support tubular Insig1 as a new therapeutic target for chronic kidney disease (CKD).

Androgens exacerbate hepatic triglyceride accumulation in rats with polycystic ovary syndrome by downregulating MTTP expression

PURPOSE

Polycystic ovary syndrome (PCOS) is a common reproductive endocrine disorder, which is closely associated with insulin resistance, glucose and lipid metabolism disorders. Patients with PCOS have a significantly higher risk of non-alcoholic fatty liver disease and are associated with hyperandrogenemia (HA). However, the exact mechanism by which HA exacerbates hepatic steatosis in PCOS has not yet been fully elucidated. This work aims to investigate the effects and underlying mechanisms of androgens on hepatic triglyceride (TG) metabolism in rats with PCOS.

METHODS

Twenty-four female Sprague-Dawley rats were randomly divided into four groups (6 rats/group): control, high-fat diet (HFD), PCOS, and PCOS + flutamide (Flu). Changes in the estrous cycle, liver and ovarian tissue sections, serum total testosterone, serum and liver biochemical indicators, and key enzymes involved in TG metabolism were studied.

RESULTS

Hepatocyte steatosis and TG accumulation were more evident in the PCOS group than in the control and HFD groups. The PCOS group showed apparent increases in the levels of serum alanine aminotransferase, aspartate aminotransferase, TG, free fatty acid, fasting insulin, and homeostasis model assessment of insulin resistance. Hepatic VLDL and apoB-100 levels decreased in the PCOS group. After Flu was administered to block the actions of androgens, the above abnormalities had been improved. The expression of MTTP was greatly decreased in the PCOS group and significantly increased after Flu administration.

CONCLUSION

Hepatic steatosis in PCOS rats was correlated with HA. Androgens may exacerbate hepatic TG accumulation by downregulating MTTP expression in PCOS.

Body composition and inflammation variables as the potential prognostic factors in epithelial ovarian cancer treated with Olaparib

Background

Epithelial ovarian cancer (EOC) is a significant cause of mortality among gynecological cancers. While Olaparib, a PARP inhibitor, has demonstrated efficacy in EOC maintenance therapy, individual responses vary. This study aims to assess the prognostic significance of body composition and systemic inflammation markers in EOC patients undergoing initial Olaparib treatment.

Methods

A retrospective analysis was conducted on 133 EOC patients initiating Olaparib therapy. Progression-free survival (PFS) was assessed through Kaplan-Meier analysis and Cox proportional hazards regression. Pre-treatment computed tomography images were utilized to evaluate body composition parameters including subcutaneous adipose tissue index (SATI), visceral adipose tissue index (VATI), skeletal muscle area index (SMI), and body mineral density (BMD). Inflammatory markers, such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), serum albumin, and hemoglobin levels, were also measured.

Results

The median follow-up duration was 16 months (range: 5-49 months). Survival analysis indicated that high SATI, high VATI, high SMI, high BMD, low NLR, and low PLR were associated with decreased risk of disease progression (all p < 0.05). Multivariate analysis identified several factors independently associated with poor PFS, including second or further lines of therapy (HR = 2.16; 95% CI = 1.09-4.27, p = 0.027), low VATI (HR = 3.79; 95% CI = 1.48-9.70, p = 0.005), low SMI (HR = 2.52; 95% CI = 1.11-5.72, p = 0.027), low BMD (HR = 2.36; 95% CI = 1.22-4.54, p = 0.010), and high NLR (HR = 0.31; 95% CI = 0.14-0.69, p = 0.004). Subgroup analysis in serous adenocarcinoma patients revealed distinct prognostic capabilities of SATI, VATI, SMI, PLR, and NLR.

Conclusion

Body composition and inflammation variables hold promise as predictors of therapeutic response to Olaparib in EOC patients. Understanding their prognostic significance could facilitate tailored treatment strategies, potentially improving patient outcomes.

The Past and Future of Inflammation as a Target to Cancer Prevention

Inflammation is an essential defense mechanism in which innate immune cells are coordinately activated on encounter of harmful stimuli, including pathogens, tissue injury, and toxic compounds and metabolites to neutralize and eliminate the instigator and initiate healing and regeneration. Properly terminated inflammation is vital to health, but uncontrolled runaway inflammation that becomes chronic begets a variety of inflammatory and metabolic diseases and increases cancer risk. Making damaged tissues behave as "wounds that do not heal" and sustaining the production of growth factors whose physiologic function is tissue healing, chronic inflammation accelerates cancer emergence from premalignant lesions. In 1863, Rudolf Virchow, a leading German pathologist, suggested a possible association between inflammation and tumor formation, but it took another 140 years to fully elucidate and appreciate the tumorigenic role of inflammation. Key findings outlined molecular events in the inflammatory cascade that promote cancer onset and progression and enabled a better appreciation of when and where inflammation should be inhibited. These efforts triggered ongoing research work to discover and develop inflammation-reducing chemopreventive strategies for decreasing cancer risk and incidence.

The transcription factor GATA6 accelerates vascular smooth muscle cell senescence-related arterial calcification by counteracting the role of anti-aging factor SIRT6 and impeding DNA damage repair

Arterial calcification is a hallmark of vascular pathology in the elderly and in individuals with chronic kidney disease (CKD). Vascular smooth muscle cells (VSMCs), after attaining a senescent phenotype, are implicated in the calcifying process. However, the underlying mechanism remains to be elucidated. Here, we reveal an aberrant upregulation of transcriptional factor GATA6 in the calcified aortas of humans, mice with CKD and mice subjected to vitamin D3 injection. Knockdown of GATA6, via recombinant adeno-associated virus carrying GATA6 shRNA, inhibited the development of arterial calcification in mice with CKD. Further gain- and loss-of function experiments in vitro verified the contribution of GATA6 in osteogenic differentiation of VSMCs. Samples of human aorta exhibited a positive relationship between age and GATA6 expression and GATA6 was also elevated in the aortas of old as compared to young mice. Calcified aortas displayed senescent features with VSMCs undergoing premature senescence, blunted by GATA6 downregulation. Notably, abnormal induction of GATA6 in senescent and calcified aortas was rescued in Sirtuin 6 (SIRT6)-transgenic mice, a well-established longevity mouse model. Suppression of GATA6 accounted for the favorable effect of SIRT6 on VSMCs senescence prevention. Mechanistically, SIRT6 inhibited the transcription of GATA6 by deacetylation and increased degradation of transcription factor Nkx2.5. Moreover, GATA6 was induced by DNA damage stress during arterial calcification and subsequently impeded the Ataxia-telangiectasia mutated (ATM)-mediated DNA damage repair process, leading to accelerated VSMCs senescence and osteogenic differentiation. Thus, GATA6 is a novel regulator in VSMCs senescence. Our findings provide novel insight in arterial calcification and a potential new target for intervention.

Longevity-Associated Transcription Factor ATF7 Promotes Healthspan by Suppressing Cellular Senescence and Systematic Inflammation

Aging is characterized by persistent low-grade systematic inflammation, which is largely responsible for the occurrence of various age-associated diseases. We and others have previously reported that long-lived people (such as centenarians) can delay the onset of or even escape certain major age-related diseases. Here, by screening blood transcriptome and inflammatory profiles, we found that long-lived individuals had a relatively lower inflammation level (IL6, TNFα), accompanied by up-regulation of activating transcription factor 7 (ATF7). Interestingly, ATF7 expression was gradually reduced during cellular senescence. Loss of ATF7 induced cellular senescence, while overexpression delayed senescence progress and senescence-associated secretory phenotype (SASP) secretion. We showed that the anti-senescence effects of ATF7 were achieved by inhibiting nuclear factor kappa B (NF-κB) signaling and increasing histone H3K9 dimethylation (H3K9me2). In Caenorhabditis elegans, ATF7 overexpression significantly suppressed aging biomarkers and extended lifespan. Our findings suggest that ATF7 is a longevity-promoting factor that lowers cellular senescence and inflammation in long-lived individuals.

From the Sun to the Cell: Examining Obesity through the Lens of Vitamin D and Inflammation

Obesity affects more than one billion people worldwide and often leads to cardiometabolic chronic comorbidities. It induces senescence-related alterations in adipose tissue, and senescence is closely linked to obesity. Fully elucidating the pathways through which vitamin D exerts anti-inflammatory effects may improve our understanding of local adipose tissue inflammation and the pathogenesis of metabolic disorders. In this narrative review, we compiled and analyzed the literature from diverse academic sources, focusing on recent developments to provide a comprehensive overview of the effect of vitamin D on inflammation associated with obesity and senescence. The article reveals that the activation of the NF-κB (nuclear factor kappa B subunit 1) and NLRP3 inflammasome (nucleotide-binding domain, leucine-rich-containing, pyrin domain-containing-3) pathways through the toll-like receptors, which increases oxidative stress and cytokine release, is a common mechanism underlying inflammation associated with obesity and senescence, and it discusses the potential beneficial effect of vitamin D in alleviating the development of subclinical inflammation. Investigating the main target cells and pathways of vitamin D action in adipose tissue could help uncover complex mechanisms of obesity and cellular senescence. This review summarizes significant findings related to opportunities for improving metabolic health.

Fatty acid oxidation regulates cellular senescence by modulating the autophagy-SIRT1 axis

Senescence, a cellular process through which damaged or dysfunctional cells suppress the cell cycle, contributes to aging or age-related functional decline. Cell metabolism has been closely correlated with aging processes, and it has been widely recognized that metabolic changes underlie the cellular alterations that occur with aging. Here, we report that fatty acid oxidation (FAO) serves as a critical regulator of cellular senescence and uncover the underlying mechanism by which FAO inhibition induces senescence. Pharmacological or genetic ablation of FAO results in a p53-dependent induction of cellular senescence in human fibroblasts, whereas enhancing FAO suppresses replicative senescence. We found that FAO inhibition promotes cellular senescence through acetyl-CoA, independent of energy depletion. Mechanistically, increased formation of autophagosomes following FAO inhibition leads to a reduction in SIRT1 protein levels, thereby contributing to senescence induction. Finally, we found that inhibition of autophagy or enforced expression of SIRT1 can rescue the induction of senescence as a result of FAO inhibition. Collectively, our study reveals a distinctive role for the FAO-autophagy-SIRT1 axis in the regulation of cellular senescence. [BMB Reports 2023; 56(12): 651-656].

Fatty acid oxidation regulates cellular senescence by modulating the autophagy-SIRT1 axis

Senescence, a cellular process through which damaged or dysfunctional cells suppress the cell cycle, contributes to aging or age-related functional decline. Cell metabolism has been closely correlated with aging processes, and it has been widely recognized that metabolic changes underlie the cellular alterations that occur with aging. Here, we report that fatty acid oxidation (FAO) serves as a critical regulator of cellular senescence and uncover the underlying mechanism by which FAO inhibition induces senescence. Pharmacological or genetic ablation of FAO results in a p53-dependent induction of cellular senescence in human fibroblasts, whereas enhancing FAO suppresses replicative senescence. We found that FAO inhibition promotes cellular senescence through acetyl-CoA, independent of energy depletion. Mechanistically, increased formation of autophagosomes following FAO inhibition leads to a reduction in SIRT1 protein levels, thereby contributing to senescence induction. Finally, we found that inhibition of autophagy or enforced expression of SIRT1 can rescue the induction of senescence as a result of FAO inhibition. Collectively, our study reveals a distinctive role for the FAO-autophagy-SIRT1 axis in the regulation of cellular senescence. [BMB Reports 2023; 56(12): 651-656].

Single-base editing in IGF2 improves meat production and intramuscular fat deposition in Liang Guang Small Spotted pigs

BACKGROUND

Chinese indigenous pigs are popular with consumers for their juiciness, flavour and meat quality, but they have lower meat production. Insulin-like growth factor 2 (IGF2) is a maternally imprinted growth factor that promotes skeletal muscle growth by regulating cell proliferation and differentiation. A single nucleotide polymorphism (SNP) within intron 3 of porcine IGF2 disrupts a binding site for the repressor, zinc finger BED-type containing 6 (ZBED6), leading to up-regulation of IGF2 and causing major effects on muscle growth, heart size, and backfat thickness. This favorable mutation is common in Western commercial pig populations, but absent in most Chinese indigenous pig breeds. To improve meat production of Chinese indigenous pigs, we used cytosine base editor 3 (CBE3) to introduce IGF2-intron3-C3071T mutation into porcine embryonic fibroblasts (PEFs) isolated from a male Liang Guang Small Spotted pig (LGSS), and single-cell clones harboring the desired mutation were selected for somatic cell nuclear transfer (SCNT) to generate the founder line of IGF2T/T pigs.

RESULTS

We found the heterozygous progeny IGF2C/T pigs exhibited enhanced expression of IGF2, increased lean meat by 18%-36%, enlarged loin muscle area by 3%-17%, improved intramuscular fat (IMF) content by 18%-39%, marbling score by 0.75-1, meat color score by 0.53-1.25, and reduced backfat thickness by 5%-16%. The enhanced accumulation of intramuscular fat in IGF2C/T pigs was identified to be regulated by the PI3K-AKT/AMPK pathway, which activated SREBP1 to promote adipogenesis.

CONCLUSIONS

We demonstrated the introduction of IGF2-intron3-C3071T in Chinese LGSS can improve both meat production and quality, and first identified the regulation of IMF deposition by IGF2 through SREBP1 via the PI3K-AKT/AMPK signaling pathways. Our study provides a further understanding of the biological functions of IGF2 and an example for improving porcine economic traits through precise base editing.

GOAT: Gene-level biomarker discovery from multi-Omics data using graph ATtention neural network for eosinophilic asthma subtype

MOTIVATION

Asthma is a heterogeneous disease where various subtypes are established and molecular biomarkers of the subtypes are yet to be discovered. Recent availability of multi-omics data paved a way to discover molecular biomarkers for the subtypes. However, multi-omics biomarker discovery is challenging because of the complex interplay between different omics layers.

RESULTS

We propose a deep attention model named Gene-level biomarker discovery from multi-Omics data using graph ATtention neural network (GOAT) for identifying molecular biomarkers for eosinophilic asthma subtypes with multi-omics data. GOAT identifies genes that discriminate subtypes using a graph neural network by modeling complex interactions among genes as the attention mechanism in the deep learning model. In experiments with multi-omics profiles of the COREA (Cohort for Reality and Evolution of Adult Asthma in Korea) asthma cohort of 300 patients, GOAT outperforms existing models and suggests interpretable biological mechanisms underlying asthma subtypes. Importantly, GOAT identified genes that are distinct only in terms of relationship with other genes through attention. To better understand the role of biomarkers, we further investigated two transcription factors, CTNNB1 and JUN, captured by GOAT. We were successful in showing the role of the transcription factors in eosinophilic asthma pathophysiology in a network propagation and transcriptional network analysis, which were not distinct in terms of gene expression level differences.

AVAILABILITY AND IMPLEMENTATION

Source code is available https://github.com/DabinJeong/Multi-omics_biomarker. The preprocessed data underlying this article is accessible in data folder of the github repository. Raw data are available in Multi-Omics Platform at http://203.252.206.90:5566/, and it can be accessible when requested.

Large-scale exome sequence analysis identifies sex- and age-specific determinants of obesity

Obesity contributes substantially to the global burden of disease and has a significant heritable component. Recent large-scale exome sequencing studies identified several genes in which rare, protein-coding variants have large effects on adult body mass index (BMI). Here we extended such work by performing sex-stratified associations in the UK Biobank study (N∼420,000). We identified genes in which rare heterozygous loss-of-function increases adult BMI in women (DIDO1, PTPRG, and SLC12A5) and in men (SLTM), with effect sizes up to ∼8 kg/m2. This is complemented by analyses implicating rare variants in OBSCN and MADD for recalled childhood adiposity. The known functions of these genes, as well as findings of common variant genome-wide pathway enrichment analyses, suggest a role for neuron death, apoptosis, and DNA damage response mechanisms in the susceptibility to obesity across the life-course. These findings highlight the importance of considering sex-specific and life-course effects in the genetic regulation of obesity.

Fatty acid oxidation facilitates DNA double-strand break repair by promoting PARP1 acetylation

DNA repair is a tightly coordinated stress response to DNA damage, which is critical for preserving genome integrity. Accruing evidence suggests that metabolic pathways have been correlated with cellular response to DNA damage. Here, we show that fatty acid oxidation (FAO) is a crucial regulator of DNA double-strand break repair, particularly homologous recombination repair. Mechanistically, FAO contributes to DNA repair by activating poly(ADP-ribose) polymerase 1 (PARP1), an enzyme that detects DNA breaks and promotes DNA repair pathway. Upon DNA damage, FAO facilitates PARP1 acetylation by providing acetyl-CoA, which is required for proper PARP1 activity. Indeed, cells reconstituted with PARP1 acetylation mutants display impaired DNA repair and enhanced sensitivity to DNA damage. Consequently, FAO inhibition reduces PARP1 activity, leading to increased genomic instability and decreased cell viability upon DNA damage. Finally, our data indicate that FAO serves as an important participant of cellular response to DNA damage, supporting DNA repair and genome stability.

Increased cell senescence in human metabolic disorders

Cell senescence (CS) is at the nexus between aging and associated chronic disorders, and aging increases the burden of CS in all major metabolic tissues. However, CS is also increased in adult obesity, type 2 diabetes (T2D), and nonalcoholic fatty liver disease independent of aging. Senescent tissues are characterized by dysfunctional cells and increased inflammation, and both progenitor cells and mature, fully differentiated and nonproliferating cells are afflicted. Recent studies have shown that hyperinsulinemia and associated insulin resistance (IR) promote CS in both human adipose and liver cells. Similarly, increased CS promotes cellular IR, showing their interdependence. Furthermore, the increased adipose CS in T2D is independent of age, BMI, and degree of hyperinsulinemia, suggesting premature aging. These results suggest that senomorphic/senolytic therapy may become important for treating these common metabolic disorders.

PTPN2 targets TAK1 for dephosphorylation to improve cellular senescence and promote adipose tissue browning in T2DM

Introduction: The energy imbalance when energy intake exceeds expenditure acts as an essential factor in the development of insulin resistance (IR). The activity of brown adipose tissue, which is involved in the dissipation of energy via heat expenditure decreases under type 2 diabetic mellitus (T2DM) state when the number of pathological aging adipocytes increases. Protein tyrosine phosphatase non-receptor type 2 (PTPN2) regulates several biological processes by dephosphorylating several cellular substrates; however, whether PTPN2 regulates cellular senescence in adipocytes and the underlying mechanism has not been reported. Methods: We constructed a model of type 2 diabetic mice with PTPN2 overexpression to explore the role of PTPN2 in T2DM. Results: We revealed that PTPN2 facilitated adipose tissue browning by alleviating pathological senescence, thus improving glucose tolerance and IR in T2DM. Mechanistically, we are the first to report that PTPN2 could bind with transforming growth factor-activated kinase 1 (TAK1) directly for dephosphorylation to inhibit the downstream MAPK/NF-κB pathway in adipocytes and regulate cellular senescence and the browning process subsequently. Discussion: Our study revealed a critical mechanism of adipocytes browning progression and provided a potential target for the treatment of related diseases.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Liraglutide promotes angiogenesis in adipose tissue via suppression of adipocyte-derived IL-6

Accumulating evidence suggests that Liraglutide is a favorable treatment for obese people. Obesity induces cellular senescence and accumulated senescent adipocytes in adipose tissue. However, the role of Liraglutide in adipose tissue (AT) senescence and the underlying mechanisms remain obscure. In this study, we found that HFD induces adipocyte senescence and impaired angiogenesis in AT. The deleterious effects provoked unhealthy adipose tissue remodeling and metabolic disturbance. In contrast, treatment of Liraglutide promoted weight reduction, alleviated adipose tissue senescence, and improved angiogenesis in AT. Notably, we demonstrated that Liraglutide promotes angiogenesis in AT dependent on adipocyte-derived IL-6. These findings revealed distinctive roles of Liraglutide in the regulation of adipocyte senescence and provide a therapeutic potential to obesity-associated metabolic disorders.

Inflammation and DNA damage: cause, effect or both

Inflammation is a biological response involving immune cells, blood vessels and mediators induced by endogenous and exogenous stimuli, such as pathogens, damaged cells or chemicals. Unresolved (chronic) inflammation is characterized by the secretion of cytokines that maintain inflammation and redox stress. Mitochondrial or nuclear redox imbalance induces DNA damage, which triggers the DNA damage response (DDR) that is orchestrated by ATM and ATR kinases, which modify gene expression and metabolism and, eventually, establish the senescent phenotype. DDR-mediated senescence is induced by the signalling proteins p53, p16 and p21, which arrest the cell cycle in G1 or G2 and promote cytokine secretion, producing the senescence-associated secretory phenotype. Senescence and inflammation phenotypes are intimately associated, but highly heterogeneous because they vary according to the cell type that is involved. The vicious cycle of inflammation, DNA damage and DDR-mediated senescence, along with the constitutive activation of the immune system, is the core of an evolutionarily conserved circuitry, which arrests the cell cycle to reduce the accumulation of mutations generated by DNA replication during redox stress caused by infection or inflammation. Evidence suggests that specific organ dysfunctions in apparently unrelated diseases of autoimmune, rheumatic, degenerative and vascular origins are caused by inflammation resulting from DNA damage-induced senescence.

Cellular rejuvenation: molecular mechanisms and potential therapeutic interventions for diseases

The ageing process is a systemic decline from cellular dysfunction to organ degeneration, with more predisposition to deteriorated disorders. Rejuvenation refers to giving aged cells or organisms more youthful characteristics through various techniques, such as cellular reprogramming and epigenetic regulation. The great leaps in cellular rejuvenation prove that ageing is not a one-way street, and many rejuvenative interventions have emerged to delay and even reverse the ageing process. Defining the mechanism by which roadblocks and signaling inputs influence complex ageing programs is essential for understanding and developing rejuvenative strategies. Here, we discuss the intrinsic and extrinsic factors that counteract cell rejuvenation, and the targeted cells and core mechanisms involved in this process. Then, we critically summarize the latest advances in state-of-art strategies of cellular rejuvenation. Various rejuvenation methods also provide insights for treating specific ageing-related diseases, including cellular reprogramming, the removal of senescence cells (SCs) and suppression of senescence-associated secretory phenotype (SASP), metabolic manipulation, stem cells-associated therapy, dietary restriction, immune rejuvenation and heterochronic transplantation, etc. The potential applications of rejuvenation therapy also extend to cancer treatment. Finally, we analyze in detail the therapeutic opportunities and challenges of rejuvenation technology. Deciphering rejuvenation interventions will provide further insights into anti-ageing and ageing-related disease treatment in clinical settings.

Ablation of miRNA-22 protects against obesity-induced adipocyte senescence and ameliorates metabolic disorders in middle-aged mice

High-fat diet (HFD) promotes obesity-related metabolic complications by activating cellular senescence in white adipose tissue (WAT). Growing evidence supports the importance of microRNA-22 (miR-22) in metabolic disorders and cellular senescence. Recently, we showed that miR-22 deletion attenuates obesity-related metabolic abnormalities. However, whether miR-22 mediates HFD-induced cellular senescence of WAT remains unknown. Here, we uncovered that obese mice displayed increased pri-miR-22 levels and cellular senescence in WAT. However, miR-22 ablation protected mice against HFD-induced WAT senescence. In addition, in vitro studies showed that miR-22 deletion prevented preadipocyte senescence in response to Doxorubicin (Doxo). Loss-of-function studies in vitro and in vivo revealed that miR-22 increases H2ax mRNA and γH2ax levels in preadipocytes and WAT without inducing DNA damage. Intriguingly, miR-22 ablation prevented HFD-induced increase in γH2ax levels and DNA damage in WAT. Similarly, miR-22 deletion prevented Doxo-induced increase in γH2ax levels in preadipocytes. Adipose miR-22 levels were enhanced in middle-aged mice fed a HFD than those found in young mice. Furthermore, miR-22 deletion attenuated fat mass gain and glucose imbalance induced by HFD in middle-aged mice. Overall, our findings indicate that miR-22 is a key regulator of obesity-induced WAT senescence and metabolic disorders in middle-aged mice.

Heterogeneity of white adipocytes in metabolic disease

PURPOSE OF REVIEW

This review aims to discuss the most recent evidence identifying the presence of distinct white adipocyte subpopulations in white adipose tissue (WAT) and how these may be altered with increasing adiposity and/or metabolic disease. We conceptualize how changes in adipocyte subpopulations may contribute to alterations in WAT function and the development of metabolic diseases such as type 2 diabetes mellitus (T2DM), nonalcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD).

RECENT FINDINGS

Studies utilizing novel analytical approaches support the existence of distinct white adipocyte subpopulations in both human and murine WAT. Adipocyte subtypes are potentially functionally distinct and may have different roles in WAT function and obesity-associated metabolic diseases.

SUMMARY

The exploration of white adipocyte heterogeneity using novel analytical technologies, has unveiled a new layer of complexity in the study of WAT biology. Interrogation of potential functional differences between adipocyte subpopulations and their role in the function of different WAT depots is now needed. Through understanding the mechanisms regulating white adipocyte subtype development and potential pathophysiological consequences of changes in the presence of adipocyte subpopulations, studies could provide novel therapeutic targets for the treatment of T2DM, NAFLD, and CVD.

Mechanic Insight into the Distinct and Common Roles of Ovariectomy Versus Adrenalectomy on Adipose Tissue Remodeling in Female Mice

Dysfunctions of the ovaries and adrenal glands are both evidenced to cause aberrant adipose tissue (AT) remodeling and resultant metabolic disorders, but their distinct and common roles are poorly understood. In this study, through biochemical, histological and RNA-seq analyses, we comprehensively explored the mechanisms underpinning subcutaneous (SAT) and visceral adipose tissue (VAT) remodeling, in response to ovariectomy (OVX) versus adrenalectomy (ADX) in female mice. OVX promoted adipocyte differentiation and fat accumulation in both SAT and VAT, by potentiating the Pparg signaling, while ADX universally prevented the cell proliferation and extracellular matrix organization in both SAT and VAT, likely by inactivating the Nr3c1 signaling, thus causing lipoatrophy in females. ADX, but not OVX, exerted great effects on the intrinsic difference between SAT and VAT. Specifically, ADX reversed a large cluster of genes differentially expressed between SAT and VAT, by activating 12 key transcription factors, and thereby caused senescent cell accumulation, massive B cell infiltration and the development of selective inflammatory response in SAT. Commonly, both OVX and ADX enhance circadian rhythmicity in VAT, and impair cell proliferation, neurogenesis, tissue morphogenesis, as well as extracellular matrix organization in SAT, thus causing dysfunction of adipose tissues and concomitant metabolic disorders.

The Synergistic Protective Effect of γ-Oryzanol (OZ) and N-Acetylcysteine (NAC) against Experimentally Induced NAFLD in Rats Entails Hypoglycemic, Antioxidant, and PPARα Stimulatory Effects

This study estimated that the combined effect of γ-Oryzanol and N-acetylcysteine (NAC) against high-fat diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) in rats also estimated some of their mechanisms of action. Adult male rats were divided into seven groups (n = 8 each) as control, control + NAC, control + γ-Oryzanol, HFD, HFD + NAC, HFD + γ-Oryzanol, and HFD + NAC + γ-Oryzanol. NAC was administered orally at a final concentration of 200 mg/kg, whereas γ-Oryzanol was added to diets at a concentration of 0.16. All treatments were conducted for 17 weeks and daily. Both NAC and γ-Oryzanol were able to reduce final body weights, fat weights, fasting glucose, fasting insulin, serum, and serum levels of liver function enzymes as well as the inflammatory markers such as tumor necrosis factor-α (TNF-α), interleukine-6 (IL-6), and leptin in HFD-fed rats. They also improved hepatic structure and glucose tolerance, increased adiponectin levels, and reduced serum and hepatic levels of triglycerides (TGs) and cholesterol (CHOL) in these rats. These effects were concomitant with a reduction in the hepatic levels of lipid peroxides (MDA) and serum levels of LDL-C, but also with an increment in the hepatic levels of superoxide dismutase (SOD) and glutathione (GSH). Interestingly, only treatment with γ-Oryzanol stimulated the mRNA levels of proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase 1 (CPT1) in the liver and white adipose tissue (WAT) of rats. Of note, the combination therapy of both drugs resulted in maximum effects and restored almost normal liver structure and basal levels of all the above-mentioned metabolic parameters. In conclusion, a combination therapy of γ-Oryzanol and NAC is an effective therapy to treat NAFLD, which can act via several mechanisms on the liver and adipose tissue.

Cold-Brewed Jasmine Tea Attenuates High-Fat Diet-Induced Obesity and Gut Microbial Dysbiosis

Cold-brewed jasmine tea (CB-JT) is regarded to possess characteristic flavors and health benefits as a novel resource of functional tea beverages. To investigate the molecular mechanisms underlying CB-JT-mediated protective effects on obesity, we evaluated the serum biochemistry, histological condition, glucose tolerance, gene expression profile and intestinal microbial diversity in high-fat diet (HFD)-fed mice. Our results demonstrate that cold-brewed jasmine tea can significantly attenuate HFD-induced body weight gain, abnormal serum lipid levels, fat deposition, hepatic injury, inflammatory processes as well as metabolic endotoxemia. CB-JT also modified the microbial community composition in HFD-fed mice and altered the balance to one closely resembled that of the control group. The differential abundance of core microbes in obese mice was reversed by CB-JT treatment, including an increment in the abundance of Blautia, Mucispirillum, and Bilophila as well as a decrease in the abundance of Alloprevotella. CB-JT was proved to regulate the mRNA expression levels of lipid metabolism-related genes such as Leptin, Pgc1a Il6, and Il1b in the adipose tissue coupled with Cyp7a1, Lxra, Srebp1c, and Atgl in the liver. These findings indicate that cold-brewed jasmine tea might be served as a potential functional tea beverage to prevent obesity and gut microbiota dysbiosis.

OPA1 Regulates Lipid Metabolism and Cold-Induced Browning of White Adipose Tissue in Mice

Mitochondria play a vital role in white adipose tissue (WAT) homeostasis including adipogenesis, fatty acid synthesis, and lipolysis. We recently reported that the mitochondrial fusion protein optic atrophy 1 (OPA1) is required for induction of fatty acid oxidation and thermogenic activation in brown adipocytes. In the current study we investigated the role of OPA1 in WAT function in vivo. We generated mice with constitutive or inducible knockout of OPA1 selectively in adipocytes. Studies were conducted under baseline conditions, at thermoneutrality, following high-fat feeding or during cold exposure. OPA1 deficiency reduced mitochondrial respiratory capacity in white adipocytes, impaired lipolytic signaling, repressed expression of de novo lipogenesis and triglyceride synthesis pathways, and promoted adipose tissue senescence and inflammation. Reduced WAT mass was associated with hepatic triglycerides accumulation and glucose intolerance. Moreover, mice deficient for OPA1 in adipocytes had impaired adaptive thermogenesis and reduced cold-induced browning of subcutaneous WAT and were completely resistant to diet-induced obesity. In conclusion, OPA1 expression and function in adipocytes are essential for adipose tissue expansion, lipid biosynthesis, and fatty acid mobilization of WAT and brown adipocytes and for thermogenic activation of brown and beige adipocytes.

Epigenetic regulation of aging: implications for interventions of aging and diseases

Aging is accompanied by the decline of organismal functions and a series of prominent hallmarks, including genetic and epigenetic alterations. These aging-associated epigenetic changes include DNA methylation, histone modification, chromatin remodeling, non-coding RNA (ncRNA) regulation, and RNA modification, all of which participate in the regulation of the aging process, and hence contribute to aging-related diseases. Therefore, understanding the epigenetic mechanisms in aging will provide new avenues to develop strategies to delay aging. Indeed, aging interventions based on manipulating epigenetic mechanisms have led to the alleviation of aging or the extension of the lifespan in animal models. Small molecule-based therapies and reprogramming strategies that enable epigenetic rejuvenation have been developed for ameliorating or reversing aging-related conditions. In addition, adopting health-promoting activities, such as caloric restriction, exercise, and calibrating circadian rhythm, has been demonstrated to delay aging. Furthermore, various clinical trials for aging intervention are ongoing, providing more evidence of the safety and efficacy of these therapies. Here, we review recent work on the epigenetic regulation of aging and outline the advances in intervention strategies for aging and age-associated diseases. A better understanding of the critical roles of epigenetics in the aging process will lead to more clinical advances in the prevention of human aging and therapy of aging-related diseases.

Cellular Senescence: The Villain of Metabolic Disease?: Discovery of a distinct senescent cell population in obesity-induced metabolic dysfunction

Senescent p21high cells in epididymal white adipose tissue (eWAT) aggravate metabolic dysfunction in obese animals. In obesity, p21high cells are specifically accumulated in stromal vascular fraction of eWAT and they have increased expression of inflammatory genes and NFκB signaling pathway. Transplantation of p21high cells provokes glucose intolerance whereas clearance of p21high cells by senolytic agents relieves insulin resistance in obese animals.

The SREBP-dependent regulation of cyclin D1 coordinates cell proliferation and lipid synthesis

The sterol regulatory-element binding protein (SREBP) family of transcription factors regulates cholesterol, fatty acid, and triglyceride synthesis and metabolism. However, they are also targeted by the ubiquitin ligase Fbw7, a major tumor suppressor, suggesting that they could regulate cell growth. Indeed, enhanced lipid synthesis is a hallmark of many human tumors. Thus, the SREBP pathway has recently emerged as a potential target for cancer therapy. We have previously demonstrated that one of these transcription factors, SREBP1, is stabilized and remains associated with target promoters during mitosis, suggesting that the expression of these target genes could be important as cells enter G1 and transcription is restored. Activation of cyclin D-cdk4/6 complexes is critical for the phosphorylation and inactivation of the retinoblastoma protein (Rb) family of transcriptional repressors and progression through the G1 phase of the cell cycle. Importantly, the cyclin D-cdk4/6-Rb regulatory axis is frequently dysregulated in human cancer. In the current manuscript, we demonstrate that SREBP1 activates the expression of cyclin D1, a coactivator of cdk4 and cdk6, by binding to an E-box in the cyclin D1 promoter. Consequently, inactivation of SREBP1 in human liver and breast cancer cell lines reduces the expression of cyclin D1 and attenuates Rb phosphorylation. Rb phosphorylation in these cells can be rescued by restoring cyclin D1 expression. On the other hand, expression of active SREBP1 induced the expression of cyclin D1 and increased the phosphorylation of Rb in a manner dependent on cyclin D1 and cdk4/6 activity. Inactivation of SREBP1 resulted in reduced expression of cyclin D1, attenuated phosphorylation of Rb, and reduced proliferation. Inactivation of SREBP1 also reduced the insulin-dependent regulation of the cyclin D1 gene. At the same time, SREBP1 is known to play an important role in supporting lipid synthesis in cancer cells. Thus, we propose that the SREBP1-dependent regulation of cyclin D1 coordinates cell proliferation with the enhanced lipid synthesis required to support cell growth.

Obesity-related kidney disease: Beyond hypertension and insulin-resistance

Chronic kidney disease (CKD) causes considerable morbidity, mortality, and health expenditures worldwide. Obesity is a significant risk factor for CKD development, partially explained by the high prevalence of diabetes mellitus and hypertension in obese patients. However, adipocytes also possess potent endocrine functions, secreting a myriad of cytokines and adipokines that contribute to insulin resistance and induce a chronic low-grade inflammatory state thereby damaging the kidney. CKD development itself is associated with various metabolic alterations that exacerbate adipose tissue dysfunction and insulin resistance. This adipose-renal axis is a major focus of current research, given the rising incidence of CKD and obesity. Cellular senescence is a biologic hallmark of aging, and age is another significant risk factor for obesity and CKD. An elevated senescent cell burden in adipose tissue predicts renal dysfunction in animal models, and senotherapies may alleviate these phenotypes. In this review, we discuss the direct mechanisms by which adipose tissue contributes to CKD development, emphasizing the potential clinical importance of such pathways in augmenting the care of CKD.