Cold-Inducible Klf9 Regulates Thermogenesis of Brown and Beige Fat

Krüppel-like factor 9 alleviates Alzheimer's disease via IDE-mediated Aβ degradation

The deposition of β-amyloid (Aβ) in the brain is a crucial factor in the pathogenesis of Alzheimer's disease (AD). Insulin-degrading enzyme (IDE) plays a critical role in the balance between Aβ production and degradation. However, the regulatory mechanisms of IDE are not yet fully understood. Therefore, uncovering additional IDE regulatory mechanisms will help elucidate the pathogenesis of AD and identify key therapeutic targets for this disease. This study revealed that global Krüppel-like factor 9-mutant (Klf9-/-) mice exhibited impaired cognitive function. Additionally, we found that Klf9 expression in hippocampal tissue was reduced in APPswe/PS1dE9 (APP/PS1) mice. This study also showed that Klf9 stimulates IDE expression and promotes the Aβ degradation process by directly binding to IDE and activating its transcription. Silencing IDE blocked the Klf9-induced Aβ degradation process. We stereotactically injected an adeno-associated virus to selectively overexpress IDE (AAV-IDE) in the hippocampal neurons of Klf9-/- mice and found that the overexpression of IDE in hippocampal neurons ameliorated cognitive deficits and reduced the Aβ content in Klf9-/- mice. Additionally, we also stereotactically injected AAV-Klf9 into the hippocampal neurons of APP/PS1 mice and found that overexpression of Klf9 in hippocampal neurons ameliorated cognitive deficits and reduced Aβ levels in APP/PS1 mice. These findings suggest that downregulation of Klf9 may be a key factor in AD progression, as it reduces Aβ clearance by decreasing IDE expression. Overexpression or activation of Klf9 may be a potential strategy for preventing the pathogenesis of AD.

Proteomics reveals genetic mechanisms of cold resistance in Hezuo pig liver tissue

Cold stress poses a significant challenge to pig farming in northern China, leading to reduced productivity and, in severe cases, even mortality. However, the mechanisms underlying cold resistance in pigs are not well understood. To explore the genetic mechanism of cold resistance in pigs under low-temperature conditions, the cold-tolerant Hezuo pig was selected as a model. DIA proteomics analysis was performed on liver tissues from Hezuo pigs after 24 h of exposure to low-temperature treatments. The results showed that approximately 149 differential abundance proteins (DAPs) were detected (95 up-regulated and 54 down-regulated). GO analysis showed that these DAPs were mainly associated with lipid metabolism, vesicle fusion, and membrane function. KEGG analysis showed that these DAPs were primarily enriched in lipid metabolism-related pathways such as cholesterol metabolism and vitamin digestion and absorption. Comprehensive analysis identified APOA4, APOA2, SREBF2, ATP23, STX2, USO1, ETFA, RAB11FIP1, ETNPPL, and SGMS1 as potential key proteins involved in cold resistance mechanisms. The mRNA expression of the genes for two key candidate proteins (APOA4 and SREBF2), which are involved in lipid metabolism, was analyzed using qRT-PCR, revealing a significant up-regulation after low-temperature treatment. These findings provide significant insights into the mechanisms of cold resistance in animals and may serve as candidate markers for further studies on cold tolerance. SIGNIFICANCE: Cold resistance is one of the key traits in pigs and involves multiple complex coordinated regulatory mechanisms. However, its genetic mechanisms are not completely understood. In this study, a DIA proteomics approach was used to identify proteins and pathways associated with cold resistance in the liver of low-temperature-treated Hezuo pigs. These findings offer novel candidate proteins and key pathways for investigating the molecular mechanisms of cold resistance in Hezuo pigs, providing a base for further elucidating the mechanisms of cold tolerance in pigs.

Klf9 promotes the repair of myocardial infarction by regulating macrophage recruitment and polarization

The inflammatory response after myocardial infarction (MI) is a precisely regulated process that greatly affects subsequent wound healing and remodeling. However, understanding about the process is still limited. Macrophages are critically involved in inflammation resolution after MI. Krüppel-like factor 9 (Klf9) is a C2H2 zinc finger-containing transcription factor that has been implicated in glucocorticoid regulation of macrophages. However, the contribution of Klf9 to macrophage phenotype and function in the context of MI remains unclear. Our study revealed that KLF9 deficiency resulted in higher mortality and cardiac rupture rate, as well as a considerable exacerbation in cardiac function. Single-cell RNA sequencing and flow cytometry analyses revealed that, compared with WT mice, Klf9-/- mice displayed excessive neutrophil infiltration, insufficient macrophage infiltration, and a reduced proportion of monocyte-derived CD206+ macrophages after MI. Moreover, the expression of IFN-γ/STAT1 pathway genes in Klf9-/- cardiac macrophages was dysregulated, characterized by insufficient expression at 1 day post-MI and excessive expression at day 3 post-MI. Mechanistically, Klf9 directly binds to the promoters of Stat1 gene, regulating its transcription. Overall, these findings indicate that Klf9 beneficially influences wound healing after MI by modulating macrophage recruitment and differentiation by regulating the IFN-γ/STAT1 signaling pathway.

Short-term heat exposure affects thermogenesis and mitophagy in goat brown adipocytes

BACKGROUND

Brown adipose tissue (BAT) has a significant impact in newborn goats on maintaining body temperature through non-shivering thermogenesis in response to cold exposure. However, the roles of heat treatment on BAT thermogenesis are still limited.

RESULTS

This study focused on the effects of short-term heat exposure on goat brown adipocytes. We found that the content of mitochondria and the proteins of UCP1 and PGC1α were increased after 12 h of heat exposure. Additionally, the triglyceride (TG) content was significantly decreased after 1, 2, 6 h of heat exposure. Furthermore, RNA-seq analysis of brown adipocytes after 12 h of heat exposure identified 1091 differentially expressed genes (DEGs). The KEGG enrichment analysis were mainly enriched in thermogenesis, fatty acid metabolism and mitophagy. In addition, we found that the amount of mitophagosomes and expression levels of mitophagy-related protein (LC3BII/LC3BI, BNIP3, and BECN) were elevated after 12 h of heat treatment.

CONCLUSION

These findings collectively indicate that heat exposure enhances the thermogenic capacity and mitophagy level of goat brown adipocytes. Our study provides evidence that heat exposure facilitates adaptive thermogenesis in goat brown adipocytes.

Downregulation of KLF9 alleviates tubulointerstitial fibrosis by modulating FABP4-mediated lipid accumulation

Tubulointerstitial fibrosis (TIF) is a significant determinant in the pathogenesis of chronic kidney disease (CKD) and is commonly concurrent with lipid infiltration in the renal tubules. Nonetheless, the precise regulatory mechanism of this phenomenon remains incompletely understood. This research sought to uncover the involvement and underlying mechanism of KLF9 in the accumulation of lipids linked to TIF. As renal fibrosis models, TGF-β1 treated HK-2 cells and a unilateral ureteral obstruction (UUO) mouse model were utilized. Histopathological analysis of kidney tissues were evaluated by hematoxylin eosin (HE), periodic acid schiff (PAS), and Masson's trichrome staining. The levels of KLF9 protein and mRNA were quantified through western blot and real-time quantitative PCR, respectively, while triglyceride (TG) levels and lipid accumulation were evaluated using a TG assay kit and Oil Red O staining, respectively. The Pearson correlation coefficient was employed to assess the relationship between KLF9 levels and lipid accumulation. To elucidate the mechanisms underlying KLF9's regulation of lipid accumulation in TIF, luciferase reporter assays, chromatin immunoprecipitation (ChIP), and rescue experiments were performed. This research identified a significant increase in KLF9 expression in TIF, correlating with lipid accumulation. The inhibition of KLF9 in HK-2 cells significantly mitigated TGF-β1 triggered fibrosis and lipid accumulation. Subsequent animal studies corroborated these findings, showing that downregulating KLF9 mitigated fibrosis and lipid accumulation. The expression level of FABP4 was considerably higher in TIF models both in vitro and in vivo. Mechanistically, KLF9 bound to the FABP4 promoter region and positively regulated the expression of FABP4. The KLF9-FABP4 pathway regulated lipid synthesis and promoted lipid accumulation, which in turn promotes the progression of TIF. Our study has unveiled the involvement of KLF9 in driving FABP4 expression at the transcriptional level, culminating in lipid accumulation and subsequent fibrosis in TIF. These findings propose that targeting lipid deposition as a therapeutic strategy may hold promise for addressing TIF.

Systematic functional characterization of non-coding regulatory SNPs associated with central obesity

Central obesity is associated with higher risk of developing a wide range of diseases independent of overall obesity. Genome-wide association studies (GWASs) have identified more than 300 susceptibility loci associated with central obesity. However, the functional understanding of these loci is limited by the fact that most loci are in non-coding regions. To address this issue, our study first prioritized 2,034 single-nucleotide polymorphisms (SNPs) based on fine-mapping and epigenomic annotation analysis. Subsequently, we employed self-transcribing active regulatory region sequencing (STARR-seq) to systematically evaluate the enhancer activity of these prioritized SNPs. The resulting data analysis identified 141 SNPs with allelic enhancer activity. Further analysis of allelic transcription factor (TF) binding prioritized 20 key TFs mediating the central-obesity-relevant genetic regulatory network. Finally, as an example, we illustrate the molecular mechanisms of how rs8079062 acts as an allele-specific enhancer to regulate the expression of its targeted RNF157. We also evaluated the role of RNF157 in the adipogenic differentiation process. In conclusion, our results provide an important resource for understanding the genetic regulatory mechanisms underlying central obesity.

Tissue adaptation to metabolic stress: insights from SUMOylation

Post-translational modification (PTM) plays a crucial role in adaptation of mammals to environmental changes, enabling them to survive in stressful situations. One such PTM is SUMO modification, which is evolutionarily conserved. It involves the covalent and reversible attachment of a small ubiquitin-like modifier (SUMO) to lysine (Lys) residues in the target protein. SUMOylation regulates various functions, including cell proliferation, differentiation, apoptosis, senescence, and maintenance of specific cellular activities. It achieves this by influencing protein-protein interactions, subcellular localization, protein stability, and DNA binding activity. Mounting evidence suggests that SUMOylation is implicated in the pathogenesis of metabolic disorders such as obesity, insulin resistance, and fatty liver. This review aims to provide an overview of the role of SUMOylation in regulating tissue adaptation to metabolic stress. Recent advancements in spectroscopic techniques have shed light on potential targets of SUMOylation and the underlying regulatory mechanisms have been elucidated, laying the theoretical foundation for the development of targeted SUMOylation interventions for metabolic syndrome while minimizing side effects.

Klf9 is essential for cardiac mitochondrial homeostasis

Mitochondrial dynamics and mitophagy are intimately linked physiological processes that are essential for cardiac homeostasis. Here we show that cardiac Krüppel-like factor 9 (Klf9) is dysregulated in human and rodent cardiomyopathy. Both global and cardiac-specific Klf9-deficient mice displayed hypertrophic cardiomyopathy. Klf9 knockout led to mitochondrial disarray and fragmentation, impairing mitochondrial respiratory function in cardiomyocytes. Furthermore, cardiac Klf9 deficiency inhibited mitophagy, thereby causing accumulation of dysfunctional mitochondria and acceleration of heart failure in response to angiotensin II treatment. In contrast, cardiac-specific Klf9 transgene improved cardiac systolic function. Mechanistically, Klf9 knockout decreased the expression of PGC-1α and its target genes involved in mitochondrial energy metabolism. Moreover, Klf9 controlled the expression of Mfn2, thereby regulating mitochondrial dynamics and mitophagy. Finally, adeno-associated virus-mediated Mfn2 rescue in Klf9-CKO hearts improved cardiac mitochondrial and systolic function. Thus, Klf9 integrates cardiac energy metabolism, mitochondrial dynamics and mitophagy. Modulating Klf9 activity may have therapeutic potential in the treatment of heart failure.

Subcutaneously transplanted xenogeneic protein recruits treg cells and M2 macrophages to induce browning of inguinal white adipose tissue

OBJECTIVE

To study whether subcutaneously embedding xenogeneic protein threads or synthetic polymer absorbable threads can improve obesity phenotypes and metabolic conditions, and to further explore its underlying mechanism.

METHODS

Thirty-six 8-week-old ob/ob mice were randomly allocated to three groups, respectively, receiving catgut embedding, PGA thread embedding or sham treatment bilaterally to the groin. Individual parameters including weight, food intake, and core temperature are recorded and metabolism assessment, energy expenditure analysis, and PET/CT scanning are also performed at fixed timepoints. After surgical incision, the inguinal white adipose tissue was histologically examined and its expression profile was tested and compared among groups 4 weeks and 12 weeks after operation.

RESULTS

Catgut embedding reduced weight gain and improved metabolic status in ob/ob mice. Browning of bilateral inguinal WAT (white adipose tissue) was induced after catgut embedding, with massive infiltration of Treg cells and M2 macrophages in the tissue slices of fat pads. IL-10 and TGF-β released by Treg cells targeted macrophages and the induced M2 macrophages increased the expression of thermogenic and anti-inflammatory genes in fat. The secretion of catecholamines by polarized M2 macrophages led to the activation of β3-AR-related pathways in adipocytes and the browning of adipose tissue.

CONCLUSIONS

Abdominal subcutaneous catgut embedding has the potential to combat obesity through the induction of WAT browning mediated by infiltrated Treg cells and macrophages.

Methyltransferase-like 3 modifications of RNAs: Implications for the pathology in the endocrine system

Methyltransferase-like 3 (METTL3) is the most well-known element of N6-methyladenosine modification on RNAs. METTL3 deposits a methyl group onto target RNAs to modify their expression, ultimately regulating various physiological and pathological events. Numerous studies have suggested the significant role of METTL3 in endocrine dysfunction and related disorders. However, reviews that summarize and interpret these studies are lacking. In this review, we systematically analyze such studies, including obesity, type 2 diabetes mellitus (T2DM), T2DM-induced diseases, pancreatic cancer, and thyroid carcinoma. This review indicates that METTL3 contributes remarkably to the endocrine dysfunction and progression of obesity, T2DM, T2DM-induced diseases, pancreatic cancer, and thyroid carcinoma. In conclusion, this review provides a comprehensive interpretation of the mechanism via which METTL3 functions on RNAs and regulates various endocrine dysfunction events and suggest potential associated correlations. Our review, thus, provides a valuable reference for further fundamental studies and clinical applications.

Glucocorticoids increase adiposity by stimulating Krüppel-like factor 9 expression in macrophages

The mechanisms underlying glucocorticoid (GC)-induced obesity are poorly understood. Macrophages are the primary targets by which GCs exert pharmacological effects and perform critical functions in adipose tissue homeostasis. Here, we show that macrophages are essential for GC-induced obesity. Dexamethasone (Dex) strongly induced Krüppel-like factor 9 (Klf9) expression in macrophages. Similar to Dex, lentivirus-mediated Klf9 overexpression inhibits M1 and M2a markers expression, causing macrophage deactivation. Furthermore, the myeloid-specific Klf9 transgene promotes obesity. Conversely, myeloid-specific Klf9-knockout (mKlf9KO) mice are lean. Moreover, myeloid Klf9 knockout largely blocks obesity induced by chronic GC treatment. Mechanistically, GC-inducible KLF9 recruits the SIN3A/HDAC complex to the promoter regions of Il6, Ptgs2, Il10, Arg1, and Chil3 to inhibit their expression, subsequently reducing thermogenesis and increasing lipid accumulation by inhibiting STAT3 signaling in adipocytes. Thus, KLF9 in macrophages integrates the beneficial anti-inflammatory and adverse metabolic effects of GCs and represents a potential target for therapeutic interventions.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

Time-restricted feeding alleviates metabolic implications of circadian disruption by regulating gut hormone release and brown fat activation

Individuals with rotating and night shift work are highly susceptible to developing metabolic disorders such as obesity and diabetes. This is primarily attributed to disruptions in the circadian rhythms caused by activities and irregular eating habits. Time-restricted feeding (tRF) limits the daily eating schedules and has been demonstrated to markedly improve several metabolic disorders. Although an intricate relationship exists between tRF and circadian rhythms, the underlying specific mechanism remains elusive. We used a sleep disruption device for activity interference and established a model of circadian rhythm disorder in mice with different genetic backgrounds. We found that circadian rhythm disruption led to abnormal hormone secretion in the gut and elevated insulin resistance. tRF improved metabolic abnormalities caused by circadian rhythm disruption, primarily by restoring the gut hormone secretion rhythm and activating brown fat thermogenesis. The crucial function of brown fat in tRF was confirmed using a mouse model with brown fat removal. We demonstrated that chenodeoxycholic acid (CDCA) effectively improved circadian rhythm disruption-induced metabolic disorders by restoring brown fat activation. Our findings demonstrate the potential benefits of CDCA in reversing metabolic disadvantages associated with irregular circadian rhythms.

Loss of Krüppel-like factor 9 deregulates both physiological gene expression and development

Krüppel-like factor 9 (Klf9) is a ubiquitously expressed transcription factor that is a feedforward regulator of multiple stress-responsive and endocrine signaling pathways. We previously described how loss of Klf9 function affects the transcriptome of zebrafish larvae sampled at a single time point 5 days post-fertilization (dpf). However, klf9 expression oscillates diurnally, and the sampled time point corresponded to its expression nadir. To determine if the transcriptomic effects of the klf9-/- mutation vary with time of day, we performed bulk RNA-seq on 5 dpf zebrafish embryos sampled at three timepoints encompassing the predawn peak and midmorning nadir of klf9 expression. We found that while the major effects of the klf9-/- mutation that we reported previously are robust to time of day, the mutation has additional effects that manifest only at the predawn time point. We used a published single-cell atlas of zebrafish development to associate the effects of the klf9-/- mutation with different cell types and found that the mutation increased mRNA associated with digestive organs (liver, pancreas, and intestine) and decreased mRNA associated with differentiating neurons and blood. Measurements from confocally-imaged larvae suggest that overrepresentation of liver mRNA in klf9-/- mutants is due to development of enlarged livers.

Progress and obstacles in transplantation of brown adipose tissue or engineered cells with thermogenic potential for metabolic benefits

Transplantation of brown adipose tissue (BAT), engineered thermogenic progenitor cells, and adipocytes have received much attention for the improvement of obesity and metabolic disorders. However, even though the thermogenic and metabolic potential exists early after transplantation, the whitening of the brown fat graft occurs with metabolic function significantly impaired. In this review, specific experiment designs, graft outcomes, and metabolic benefits for the transplantation of BAT or engineered cells will be discussed. The current advancements will offer guidance to further investigation, and the obstacles appearing in previous studies will require innovation of BAT transplantation methods.

Stress-inducible IL-6 is regulated by KLF7 in brown adipocytes

Stress-inducible interleukin 6 (IL-6) is generated in brown adipocytes via beta-3 adrenergic receptor (ADRB3) signaling, which is necessary in stress hyperglycemia, the kind of metabolic adaptation enabling "fight or flight" response by means of liver gluconeogenesis. Nevertheless, the mechanism of ADRB3 signaling mediates IL-6 in brown adipocytes remains unclear. As a result, it is critical to understand how brown adipocytes produce IL-6 via ADRB3 signaling. We found that the ADRB3 agonist and cold stimulation promoted the expression of KLF7 and IL-6 in brown adipocytes of mice. In parallel to these results in vivo, treatment with ADRB3 agonist promoted the expression of KLF7 and the release of IL-6 in primary brown adipocytes of mice. Notably, we discovered that KLF7 positively controls the expression of IL-6 and downregulated KLF7 largely blunted ADRB3 agonist induced IL-6 expressions in brown adipocytes. Our findings suggest that KLF7 is required for the generation of IL-6 when ADRB3 signaling is activated in brown adipocytes.

Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity

BACKGROUND

The triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes.

APPROACH AND RESULTS

We demonstrated that MTP is present on lipid droplets in human adipocytes. Adipose-specific MTP deficient (A-Mttp^-/-) male and female mice fed an obesogenic diet gained less weight than Mttp^f/f mice, had less fat mass, smaller adipocytes and were insulin sensitive. A-Mttp^-/- mice showed higher energy expenditure than Mttp^f/f mice. During a cold challenge, A-Mttp^-/- mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL.

CONCLUSION

Our findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP.

Exercise training rescues adipose tissue spexin expression and secretion in diet-induced obese mice

Exercise training improves obesity-induced metabolic diseases through regulation of adipokines. Previous studies have shown that adipocyte-spexin participates in metabolic diseases such as obesity and diabetes via the modulation of energy homeostasis and insulin resistance. The objective of this research was to investigate the effects of swimming exercise on the levels of adipocyte-spexin and the underlying mechanisms. The normal chow diet (NC)-fed and high-fat diet (HFD)-fed mice were divided into exercise or sedentary groups. The expression and secretion of spexin in adipose tissue were assessed by quantitative real-time PCR and ELISA. The present findings uncovered the effect of exercise-induced spexin expression in the adipose tissue of obese mice. Besides, chronic exercise-induced upregulation of adipose spexin may be mediated by COUP-TF2 and KLF9. In addition, constant-moderate intensity exercise increased the levels of GLUT4, SIRT1 and PGC-1α in the skeletal muscles of mice. These results suggest that spexin is a potential mediator for exercise to ameliorate obesity-induced insulin resistance, namely, the beneficial effect of exercise on insulin sensitivity is at least partly mediated by spexin. Thus, exercise restores spexin production and release, which increases insulin sensitivity and maintains metabolic balance in the adipose tissues of HFD-induced obese mice.

Transcription factor Klf9 controls bile acid reabsorption and enterohepatic circulation in mice via promoting intestinal Asbt expression

Bile acid (BA) homeostasis is regulated by the extensive cross-talk between liver and intestine. Many bile-acid-activated signaling pathways have become attractive therapeutic targets for the treatment of metabolic disorders. In this study we investigated the regulatory mechanisms of BA in the intestine. We showed that the BA levels in the gallbladder and faeces were significantly increased, whereas serum BA levels decreased in systemic Krüppel-like factor 9 (Klf9) deficiency (Klf9-/-) mice. These phenotypes were also observed in the intestine-specific Klf9-deleted (Klf9vil-/-) mice. In contrast, BA levels in the gallbladder and faeces were reduced, whereas BA levels in the serum were increased in intestinal Klf9 transgenic (Klf9Rosa26+/+) mice. By using a combination of biochemical, molecular and functional assays, we revealed that Klf9 promoted the expression of apical sodium-dependent bile acid transporter (Asbt) in the terminal ileum to enhance BA absorption in the intestine. Reabsorbed BA affected liver BA synthetic enzymes by regulating Fgf15 expression. This study has identified a previously neglected transcriptional pathway that regulates BA homeostasis.

Krüppel-like Factor 9 (KLF9) Suppresses Hepatocellular Carcinoma (HCC)-Promoting Oxidative Stress and Inflammation in Mice Fed High-Fat Diet

Obesity, oxidative stress, and inflammation are risk factors for hepatocellular carcinoma (HCC). We examined, in mice, the effects of Krüppel-like factor 9 (KLF9) knockout on: adiposity, hepatic and systemic oxidative stress, and hepatic expression of pro-inflammatory and NOX/DUOX family genes, in a high-fat diet (HFD) context. Male and female Klf9^+/+ (wild type, WT) and Klf9^-/- (knockout, KO) mice were fed HFD (beginning at age 35 days) for 12 weeks, after which liver and adipose tissues were obtained, and serum adiponectin and leptin levels, liver fat content, and markers of oxidative stress evaluated. Klf9^-/- mice of either sex did not exhibit significant alterations in weight gain, adipocyte size, adipokine levels, or liver fat content when compared to WT counterparts. However, Klf9^-/- mice of both sexes had increased liver weight/size (hepatomegaly). This was accompanied by increased hepatic oxidative stress as indicated by decreased GSH/GSSG ratio and increased homocysteine, 3-nitrotyrosine, 3-chlorotyrosine, and 4HNE content. Decreased GSH to GSSG ratio and a trend toward increased homocysteine levels were observed in the corresponding Klf9^-/- mouse serum. Gene expression analysis showed a heightened pro-inflammatory state in livers from Klf9^-/- mice. KLF9 suppresses hepatic oxidative stress and inflammation, thus identifying potential mechanisms for KLF9 suppression of HCC and perhaps cancers of other tissues.

Adipose tissue spexin in physical exercise and age-associated diseases

It is known that a strong association exists between a suboptimal lifestyle (physical inactivity and sedentary behavior and/or high calorie diet) and increased propensity of developing age-associated diseases, such as obesity and T2DM. Physical exercise can alleviate obesity-induced insulin resistance and T2DM, however, the precise mechanism for this outcome is not fully understood. The endocrine disorder of adipose tissue in obesity plays a critical role in the development of insulin resistance. In this regard, spexin has been recently described as an adipokine that plays an important role in the pathophysiology of obesity-induced insulin resistance and T2DM. In obese states, expression of adipose tissue spexin is reduced, inducing the adipose tissue and skeletal muscle more susceptible to insulin resistance. Emerging evidences point out that exercise can increase spexin expression. In return, spexin could exert the exercise-protective roles to ameliorate insulin resistance, suggesting that spexin is a potential mediator for exercise to ameliorate obesity-induced insulin resistance and T2DM, namely, the beneficial effect of exercise on insulin sensitivity is at least partly mediated by spexin. This review summarizes our and others' recent studies regarding the effects of obesity on adipose tissue spexin induction, along with the potential effect of exercise on this response in obese context, and provides a new insight into the multivariate relationship among exercise, spexin and T2DM. It should be therefore taken into account that a combination of spexin and exercise training is an effective therapeutic strategy for age-associated diseases.

miR-27a Regulates Sheep Adipocyte Differentiation by Targeting CPT1B Gene

Simple Summary

The content of intramuscular fat (IMF) is the main determinant of the nutritional and economic value of sheep meat. Therefore, lipid synthesis in sheep longissimus lumborum (LL) has become an important research focus. MicroRNA-27a (miR-27a) has been shown to play a crucial role in the proliferation and differentiation of adipocyte progenitor cells. In this study, we revealed that miR-27a significantly inhibited the formation of lipid droplets by targeting CPT1B to inhibit genes involved in lipid synthesis including PPAR γ, SCD, LPL, and FABP4. Here, we constructed a miR-27a-CPT1B regulatory network map, which revealed the interaction between miR-27a and CPT1B in lipid synthesis in ovine preadipocytes.

Abstract

MiRNAs are vital regulators and play a major role in cell differentiation, biological development, and disease occurrence. In recent years, many studies have found that miRNAs are involved in the proliferation and differentiation of adipocytes. The objective of this study was to evaluate the effect of miR-27a and its target gene CPT1B on ovine preadipocytes differentiation in Small-tailed Han sheep (Ovis aries). Down-regulation of miR-27a significantly promoted the production of lipid droplets, while overexpression of miR-27a led to a reduction in lipid droplet production. In addition, inhibition of miR-27a led to a significant increase in the expression of genes involved in lipid synthesis, including PPAR γ, SCD, LPL, and FABP4. Target Scan software predicted that CPT1B is a new potential target gene of miR-27a. Further experiments revealed that CPT1B gene expression and protein levels were negatively correlated with miR-27a expression. Overexpression of miR-27a led to a significant decrease in CPT1B mRNA levels and inhibited the accumulation of lipid droplets and vice versa. Moreover, overexpression of CPT1B promoted the synthesis of lipid droplets in ovine preadipocytes. Furthermore, luciferase reporter assays confirmed CPT1B to be a miR-27a direct target gene. This study confirmed that miR-27a increases the expression of genes related to lipid synthesis in ovine preadipocytes by targeting CPT1B, thereby promoting the synthesis of lipid droplets. The results of this study can be used to be exploited in devising novel approaches for improving the IMF content of sheep.

Glucocorticoid-Mediated Developmental Programming of Vertebrate Stress Responsivity

Glucocorticoids, vertebrate steroid hormones produced by cells of the adrenal cortex or interrenal tissue, function dynamically to maintain homeostasis under constantly changing and occasionally stressful environmental conditions. They do so by binding and thereby activating nuclear receptor transcription factors, the Glucocorticoid and Mineralocorticoid Receptors (MR and GR, respectively). The GR, by virtue of its lower affinity for endogenous glucocorticoids (cortisol or corticosterone), is primarily responsible for transducing the dynamic signals conveyed by circadian and ultradian glucocorticoid oscillations as well as transient pulses produced in response to acute stress. These dynamics are important determinants of stress responsivity, and at the systemic level are produced by feedforward and feedback signaling along the hypothalamus-pituitary-adrenal/interrenal axis. Within receiving cells, GR signaling dynamics are controlled by the GR target gene and negative feedback regulator fkpb5. Chronic stress can alter signaling dynamics via imperfect physiological adaptation that changes systemic and/or cellular set points, resulting in chronically elevated cortisol levels and increased allostatic load, which undermines health and promotes development of disease. When this occurs during early development it can "program" the responsivity of the stress system, with persistent effects on allostatic load and disease susceptibility. An important question concerns the glucocorticoid-responsive gene regulatory network that contributes to such programming. Recent studies show that klf9, a ubiquitously expressed GR target gene that encodes a Krüppel-like transcription factor important for metabolic plasticity and neuronal differentiation, is a feedforward regulator of GR signaling impacting cellular glucocorticoid responsivity, suggesting that it may be a critical node in that regulatory network.

Glucocorticoid-Responsive Transcription Factor Krüppel-Like Factor 9 Regulates fkbp5 and Metabolism

Krüppel-like factor 9 (Klf9) is a feedforward regulator of glucocorticoid receptor (GR) signaling. Here we show that in zebrafish klf9 is expressed with GR-dependent oscillatory dynamics in synchrony with fkbp5, a GR target that encodes a negative feedback regulator of GR signaling. We found that fkbp5 transcript levels are elevated in klf9 -/- mutants and that Klf9 associates with chromatin at the fkbp5 promoter, which becomes hyperacetylated in klf9 -/ - mutants, suggesting that the GR regulates fkbp5 via an incoherent feedforward loop with klf9. As both the GR and Fkbp5 are known to regulate metabolism, we asked how loss of Klf9 affects metabolic rate and gene expression. We found that klf9 -/- mutants have a decreased oxygen consumption rate (OCR) and upregulate glycolytic genes, the promoter regions of which are enriched for potential Klf9 binding motifs. Our results suggest that Klf9 functions downstream of the GR to regulate cellular glucocorticoid responsivity and metabolic homeostasis.

Tripartite motif 16 ameliorates nonalcoholic steatohepatitis by promoting the degradation of phospho-TAK1

Nonalcoholic steatohepatitis (NASH)-related hepatocellular carcinoma and liver disorders have become the leading causes for the need of liver transplantation in developed countries. Lipotoxicity plays a central role in NASH progression by causing endoplasmic reticulum stress and disrupting protein homeostasis. To identify key molecules that mitigate the detrimental consequences of lipotoxicity, we performed integrative multiomics analysis and identified the E3 ligase tripartite motif 16 (TRIM16) as a candidate molecule. In particular, we found that lipid accumulation and inflammation in a mouse NASH model is mitigated by TRIM16 overexpression but aggravated by its depletion. Multiomics analysis showed that TRIM16 suppressed NASH progression by attenuating the activation of the mitogen-activated protein kinase (MAPK) signaling pathway; specifically, by preferentially interacting with phospho-TAK1 to promote its degradation. Together, these results identify TRIM16 as a promising therapeutic target for the treatment of NASH.

Thermogenic Fat: Development, Physiological Function, and Therapeutic Potential

The concerning worldwide increase of obesity and chronic metabolic diseases, such as T2D, dyslipidemia, and cardiovascular disease, motivates further investigations into preventive and alternative therapeutic approaches. Over the past decade, there has been growing evidence that the formation and activation of thermogenic adipocytes (brown and beige) may serve as therapy to treat obesity and its associated diseases owing to its capacity to increase energy expenditure and to modulate circulating lipids and glucose levels. Thus, understanding the molecular mechanism of brown and beige adipocytes formation and activation will facilitate the development of strategies to combat metabolic disorders. Here, we provide a comprehensive overview of pathways and players involved in the development of brown and beige fat, as well as the role of thermogenic adipocytes in energy homeostasis and metabolism. Furthermore, we discuss the alterations in brown and beige adipose tissue function during obesity and explore the therapeutic potential of thermogenic activation to treat metabolic syndrome.

Glycerol Monocaprylate Modulates Gut Microbiota and Increases Short-Chain Fatty Acids Production without Adverse Effects on Metabolism and Inflammation

Glycerol monocaprylate (GMC) is a glycerol derivative of medium-chain fatty acids (MCFAs) and is widely used as a preservative in food processing. However, GMC and its hydrolytic acid (octylic acid) have antibacterial properties that may affect the physiology and intestinal microecology of the human body. Therefore, in this study, the effects of two different dosages of GMC (150 and 1600 mg kg-1) on glucose, lipid metabolism, inflammation, and intestinal microecology of normal diet-fed C57BL/6 mice were comprehensively investigated. The obtained results showed that the level of triglycerides (TGs) in the low-dose group down-regulated significantly, and the anti-inflammatory cytokine interleukin 10 (IL-10) significantly increased, while the pro-inflammatory cytokines monocyte chemotactic protein 1 (MCP-1) and interleukin 1beta (IL-1β) in the high-dose group were significantly decreased. Importantly, GMC promoted the α-diversity of gut microbiota in normal-diet-fed mice, regardless of dosages. Additionally, it was found that the low-dose treatment of GMC significantly increased the abundance of Lactobacillus, while the high-dose treatment of GMC significantly increased the abundance of SCFA-producers such as Clostridiales, Lachnospiraceae, and Ruminococcus. Moreover, the content of short-chain fatty acids (SCFAs) was significantly increased by GMC supplementation. Thus, our research provides a novel insight into the effects of GMC on gut microbiota and physiological characteristics.