The Mechanism of Leptin on Inhibiting Fibrosis and Promoting Browning of White Fat by Reducing ITGA5 in Mice

Impact of leptin on postoperative peritoneal adhesion formations in colorectal resection

PURPOSE

Postoperative peritoneal adhesion formation (PAF) is a distressing complication. Leptin, secreted by fat tissues, may be associated with PAF. However, the relationships between PAF and leptin are unclear. This study investigated the impact of leptin on PAF after colorectal tumor resection.

METHODS

A cecum cauterization mouse model was used to investigate PAF and its association with leptin. Mice adhesion score (AS) was evaluated on day 7 after treatment. The clinical study included patients who underwent elective colorectal resection with temporary ileostomy between April 2021 and December 2024. The AS was evaluated at the time of ileostomy closure. Patients with the highest AS quartile were classified into the high-AS group; clinical factors associated with PAF were examined. An enzyme-linked immunosorbent assay was used to measure human and murine serum leptin concentrations.

RESULTS

The animal experiment revealed that serum leptin levels on postoperative day 7 were negatively correlated with mice ASs (P = 0.0043, r = -0.6241). In a clinical study, eight patients had a high AS (27.6%). Visceral fat mass and preoperative serum leptin levels were higher in the high-AS group than in the low-AS group. The serum leptin ratio (postoperative value to preoperative value) on postoperative day 7 was lower in the high-AS group. In multivariate analysis, the serum leptin ratio was an independent factor for classifying into the high-AS group.

CONCLUSIONS

A decrease in postoperative serum leptin levels was associated with severe PAF. Leptin may be a novel key molecule in PAF.

Impact of age on cardiometabolic health in children at adiposity rebound: the role of genetic mechanisms

BACKGROUND

Identifying effective predictors early in life is crucial to enable timely prevention and intervention to improve cardiometabolic health outcomes. Adiposity rebound (AR) is an important period in early life, with earlier AR increasing the risk of cardiometabolic abnormalities. However, the role and mechanism of genetic factors in this association are unclear. Therefore, this study reviews the potential genetic mechanisms influencing the age at AR, as well as the genetic mechanisms linking earlier AR with cardiometabolic abnormalities.

DATA SOURCES

A comprehensive literature search was conducted in PubMed and China National Knowledge Infrastructure databases using a combination of medical subject headings terms and related keywords, including "adiposity rebound", "cardiometabolic", "obesity", "BMI trajectory", "diabetes mellitus", "dyslipidemias", "hypertension", "metabolic syndrome", "genetics", and "epigenetic". Citation tracking was performed as a supplementary search strategy. All potentially relevant articles were subsequently subjected to full-text evaluation for eligibility assessment.

RESULTS

Polymorphisms in the DMRT1, FTO, LEPR, and TFAP2B genes, along with obesity susceptibility, can influence the age at AR. Single-nucleotide polymorphisms associated with the age at AR are enriched in the insulin-like growth factor 1 (IGF-1) signaling pathway, which can be modulated by the LEPR and TFAP2B genes. Shared genetic mechanisms between cardiometabolic abnormalities and the age at AR are influenced by obesity-related genetic variants. These variants regulate the growth hormone (GH)/IGF-1 axis, advancing AR and leading to cardiometabolic abnormalities. Earlier AR alters adiponectin and leptin levels, further activating the GH/IGF-1 axis and creating a vicious cycle. Long-term breastfeeding can counteract the adverse effects of obesity-related genetic susceptibility on AR timing, thereby reducing the genetic risk of cardiometabolic abnormalities.

CONCLUSIONS

Our results support earlier AR as a marker for identifying cardiometabolic risk and screening high-risk populations at the genetic level.

Elevated PRELP expression in heart and liver fibrosis promotes collagen production

Fibrosis results from the excessive production of extracellular matrix proteins by myofibroblasts. It has recently been reported that in the heart, myofibroblasts develop chondrocyte-like properties following myocardial infarction as fibrosis progresses and tissues stiffen. However, the nature of these chondrocyte-like myofibroblasts remains unclear. In this study, we found that the expression of the proline- and arginine-rich end leucine-rich repeat protein (PRELP) was upregulated in hearts and livers stiffened by fibrosis with chronic inflammation. Moreover, we established that Prelp was specifically expressed in chondrocyte-like myofibroblasts. Prelp expression was found to be regulated by the transcription factor SOX9, and in cardiac and liver myofibroblasts, Prelp-knockdown was observed to reduce collagen expression. These findings reveal that PRELP is specifically expressed in chondrocyte-like myofibroblasts and that it promotes collagen production. PRELP could thus serve as a novel therapeutic target for treating fibrosis.

TGF-β antagonism synergizes with PPARγ agonism to reduce fibrosis and enhance beige adipogenesis

OBJECTIVES

Adipose tissue depots vary markedly in their ability to store and metabolize triglycerides, undergo beige adipogenesis and susceptibility to metabolic disease. The molecular mechanisms that underlie such heterogeneity are not entirely clear. Previously, we showed that TGF-β signaling suppresses beige adipogenesis via repressing the recruitment of dedicated beige progenitors. Here, we find that TGF-β signals dynamically regulate the balance between adipose tissue fibrosis and beige adipogenesis.

METHODS

We investigated adipose tissue depot-specific differences in activation of TGF-β signaling in response to dietary challenge. RNA-seq and fluorescence activated cell sorting was performed to identify and characterize cells responding to changes in TGF-β signaling status. Mouse models, pharmacological strategies and human adipose tissue analyses were performed to further define the influence of TGF-β signaling on fibrosis and functional beige adipogenesis.

RESULTS

Elevated basal and high-fat diet inducible activation of TGF-β/Smad3 signaling was observed in the visceral adipose tissue depot. Activation of TGF-β/Smad3 signaling was associated with increased adipose tissue fibrosis. RNA-seq combined with fluorescence-activated cell sorting of stromal vascular fraction of epididymal white adipose tissue depot resulted in identification of TGF-β/Smad3 regulated ITGA5+ fibrogenic progenitors. TGF-β/Smad3 signal inhibition, genetically or pharmacologically, reduced fibrosis and increased functional beige adipogenesis. TGF-β/Smad3 antagonized the beneficial effects of PPARγ whereas TGF-β receptor 1 inhibition synergized with actions of rosiglitazone, a PPARγ agonist, to dampen fibrosis and promote beige adipogenesis. Positive correlation between TGF-β activation and ITGA5 was observed in human adipose tissue, with visceral adipose tissue depots exhibiting higher fibrosis potential than subcutaneous or brown adipose tissue depots.

CONCLUSIONS

Basal and high-fat diet inducible activation of TGF-β underlies the heterogeneity of adipose tissue depots. TGF-β/Smad3 activation promotes adipose tissue fibrosis and suppresses beige progenitors. Together, these dual mechanisms preclude functional beige adipogenesis. Controlled inhibition of TβRI signaling and concomitant PPARγ stimulation can suppress adipose tissue fibrosis and promote beige adipogenesis to improve metabolism.

Role of miRNA-mRNA Interactome in Pathophysiology of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy is an inherited entity characterized by irregular cell-cell adhesion, cardiomyocyte death and fibro-fatty replacement of ventricular myocytes, leading to malignant ventricular arrythmias, contractile dysfunction and sudden cardiac death. Pathogenic variants in genes that encode desmosome are the predominant cause of arrhythmogenic cardiomyopathy. Moreover, signalling pathways such as Wnt/ß-catenin and transforming growth factor-β have been involved in the disease progression. However, still little is known about the molecular pathophysiological mechanisms that underlie arrhythmogenic cardiomyopathy pathogenesis. We used mRNA and small RNA sequencing to analyse the transcriptome of health and arrhythmogenic cardiomyopathy of autopsied human hearts. Our results showed 697 differentially expressed genes and eight differentially expressed miRNAs. Functional enrichment revealed mitochondrial respiratory-related pathways, impaired response to oxidative stress, apoptotic signalling pathways and inflammatory response-related and extracellular matrix response pathways. Furthermore, analysis of the miRNA-mRNA interactome identified eleven negatively correlated miRNA-target pairs for arrhythmogenic cardiomyopathy. Our finding revealed novel arrhythmogenic cardiomyopathy-related miRNAs with important regulatory function in disease pathogenesis, highlighting their value as potential key targets for therapeutic approaches.

A Preliminary Study on Factors That Drive Patient Variability in Human Subcutaneous Adipose Tissues

Adipose tissue is a dynamic regulatory organ that has profound effects on the overall health of patients. Unfortunately, inconsistencies in human adipose tissues are extensive and multifactorial, including large variability in cellular sizes, lipid content, inflammation, extracellular matrix components, mechanics, and cytokines secreted. Given the high human variability, and since much of what is known about adipose tissue is from animal models, we sought to establish correlations and patterns between biological, mechanical, and epidemiological properties of human adipose tissues. To do this, twenty-six independent variables were cataloged for twenty patients, which included patient demographics and factors that drive health, obesity, and fibrosis. A factorial analysis for mixed data (FAMD) was used to analyze patterns in the dataset (with BMI > 25), and a correlation matrix was used to identify interactions between quantitative variables. Vascular endothelial growth factor A (VEGFA) and actin alpha 2, smooth muscle (ACTA2) gene expression were the highest loadings in the first two dimensions of the FAMD. The number of adipocytes was also a key driver of patient-related differences, where a decrease in the density of adipocytes was associated with aging. Aging was also correlated with a decrease in overall lipid percentage of subcutaneous tissue, with lipid deposition being favored extracellularly, an increase in transforming growth factor-β1 (TGFβ1), and an increase in M1 macrophage polarization. An important finding was that self-identified race contributed to variance between patients in this study, where Black patients had significantly lower gene expression levels of TGFβ1 and ACTA2. This finding supports the urgent need to account for patient ancestry in biomedical research to develop better therapeutic strategies for all patients. Another important finding was that TGFβ induced factor homeobox 1 (TGIF1), an understudied signaling molecule, which is highly correlated with leptin signaling, was correlated with metabolic inflammation. Furthermore, this study draws attention to what we define as "extracellular lipid droplets", which were consistently found in collagen-rich regions of the obese adipose tissues evaluated here. Reduced levels of TGIF1 were correlated with higher numbers of extracellular lipid droplets and an inability to suppress fibrotic changes in adipose tissue. Finally, this study indicated that M1 and M2 macrophage markers were correlated with each other and leptin in patients with a BMI > 25. This finding supports growing evidence that macrophage polarization in obesity involves a complex, interconnecting network system rather than a full switch in activation patterns from M2 to M1 with increasing body mass. Overall, this study reinforces key findings in animal studies and identifies important areas for future research, where human and animal studies are divergent. Understanding key drivers of human patient variability is required to unravel the complex metabolic health of unique patients.

Challenges and opportunities in obesity: the role of adipocytes during tissue fibrosis

Obesity is a chronic disease that affects the energy balance of the whole body. In addition to increasing fat mass, tissue fibrosis occurred in white adipose tissue in obese condition. Fibrosis is the over-activation of fibroblasts leading to excessive accumulation of extracellular matrix, which could be caused by various factors, including the status of adipocytes. The morphology of adipocytes responds rapidly and dynamically to nutrient fluctuations. Adaptive hypertrophy of normal adipocytes protects peripheral organs from damage from lipotoxicity. However, the biological behavior of hypertrophic adipocytes in chronic obesity is abnormally altered. Adipocytes lead to fibrotic remodeling of the extracellular matrix by inducing unresolved chronic inflammation, persistent hypoxia, and increasing myofibroblast numbers. Moreover, adipocyte-induced fibrosis not only restricts the flexible expansion and contraction of adipose tissue but also initiates the development of various diseases through cellular autonomic and paracrine effects. Regarding anti-fibrotic therapy, dysregulated intracellular signaling and epigenetic changes represent potential candidate targets. Thus, modulation of adipocytes may provide potential therapeutic avenues for reversing pathological fibrosis in adipose tissue and achieving the anti-obesity purpose.

MHO or MUO? White adipose tissue remodeling

In this review, we delve into the intricate relationship between white adipose tissue (WAT) remodeling and metabolic aspects in obesity, with a specific focus on individuals with metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUO). WAT is a highly heterogeneous, plastic, and dynamically secreting endocrine and immune organ. WAT remodeling plays a crucial role in metabolic health, involving expansion mode, microenvironment, phenotype, and distribution. In individuals with MHO, WAT remodeling is beneficial, reducing ectopic fat deposition and insulin resistance (IR) through mechanisms like increased adipocyte hyperplasia, anti-inflammatory microenvironment, appropriate extracellular matrix (ECM) remodeling, appropriate vascularization, enhanced WAT browning, and subcutaneous adipose tissue (SWAT) deposition. Conversely, for those with MUO, WAT remodeling leads to ectopic fat deposition and IR, causing metabolic dysregulation. This process involves adipocyte hypertrophy, disrupted vascularization, heightened pro-inflammatory microenvironment, enhanced brown adipose tissue (BAT) whitening, and accumulation of visceral adipose tissue (VWAT) deposition. The review underscores the pivotal importance of intervening in WAT remodeling to hinder the transition from MHO to MUO. This insight is valuable for tailoring personalized and effective management strategies for patients with obesity in clinical practice.

Leptin deficiency impairs adipogenesis and browning response in mouse mesenchymal progenitors

Although phenotypically different, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) are able to produce heat through non-shivering thermogenesis due to the presence of mitochondrial uncoupling protein 1 (UCP1). The appearance of thermogenically active beige adipocytes in iWAT is known as browning. Both brown and beige cells originate from mesenchymal stem cells (MSCs), and in culture conditions a browning response can be induced with hypothermia (i.e. 32 °C) during which nuclear leptin immunodetection was observed. The central role of leptin in regulating food intake and energy consumption is well recognised, but its importance in the browning process at the cellular level is unclear. Here, immunocytochemical analysis of MSC-derived adipocytes established nuclear localization of both leptin and leptin receptor suggesting an involvement of the leptin pathway in the browning response. In order to elucidate whether leptin modulates the expression of brown and beige adipocyte markers, BAT and iWAT samples from leptin-deficient (ob/ob) mice were analysed and exhibited reduced brown/beige marker expression compared to wild-type controls. When MSCs were isolated and differentiated into adipocytes, leptin deficiency was observed to induce a white phenotype, especially when incubated at 32 °C. These adaptations were accompanied with morphological signs of impaired adipogenic differentiation. Overall, our results indicate that leptin supports adipocyte browning and suggest a potential role for leptin in adipogenesis and browning.

Comparative study of lung toxicity of E-cigarette ingredients to investigate E-cigarette or vaping product associated lung injury

No comparative study has yet been performed on the respiratory effects of individual E-cigarette ingredients. Here, lung toxicity of individual ingredients of E-cigarette products containing nicotine or tetrahydrocannabinol was investigated. Mice were intratracheally administered propylene glycol (PG), vegetable glycerin (VG), vitamin E acetate (VEA), or nicotine individually for two weeks. Cytological and histological changes were noticed in PG- and VEA-treated mice that exhibited pathophysiological changes which were associated with symptoms seen in patients with symptoms of E-cigarette or Vaping Use-Associated Lung Injuries (EVALI) or E-cigarette users. Compared to potential human exposure situations, while the VEA exposure condition was similar to the dose equivalent of VEA content in E-cigarettes, the PG condition was about 47-137 times higher than the dose equivalent of the daily PG intake of E-cigarette users. These results reveal that VEA exposure is much more likely to cause problems related to EVALI in humans than PG. Transcriptomic analysis revealed that PG exposure was associated with fibrotic lung injury via the AKT signaling pathway and M2 macrophage polarization, and VEA exposure was associated with asthmatic airway inflammation via the mitogen-activated protein kinase signaling pathway. This study provides novel insights into the pathophysiological effects of individual ingredients of E-cigarettes.

Loss of C3a and C5a receptors promotes adipocyte browning and attenuates diet-induced obesity via activating inosine/A2aR pathway

Complement activation is thought to underline the pathologic progression of obesity-related metabolic disorders; however, its role in adaptive thermogenesis has scarcely been explored. Here, we identify complement C3a receptor (C3aR) and C5a receptor (C5aR) as critical switches to control adipocyte browning and energy balance in male mice. Loss of C3aR and C5aR in combination, more than individually, increases cold-induced adipocyte browning and attenuates diet-induced obesity in male mice. Mechanistically, loss of C3aR and C5aR increases regulatory T cell (Treg) accumulation in the subcutaneous white adipose tissue during cold exposure or high-fat diet. Activated Tregs produce adenosine, which is converted to inosine by adipocyte-derived adenosine deaminases. Inosine promotes adipocyte browning in a manner dependent on activating adenosine A2a receptor. These data reveal a regulatory mechanism of complement in controlling adaptive thermogenesis and suggest that targeting the C3aR/C5aR pathways may represent a therapeutic strategy in treating obesity-related metabolic diseases.

The Combined Partial Knockdown of CBS and MPST Genes Induces Inflammation, Impairs Adipocyte Function-Related Gene Expression and Disrupts Protein Persulfidation in Human Adipocytes

Recent studies in mice and humans demonstrated the relevance of H₂S synthesising enzymes, such as CTH, CBS, and MPST, in the physiology of adipose tissue and the differentiation of preadipocyte into adipocytes. Here, our objective was to investigate the combined role of CTH, CBS, and MPST in the preservation of adipocyte protein persulfidation and adipogenesis. Combined partial CTH, CBS, and MPST gene knockdown was achieved treating fully human adipocytes with siRNAs against these transcripts (siRNA_MIX). Adipocyte protein persulfidation was analyzed using label-free quantitative mass spectrometry coupled with a dimedone-switch method for protein labeling and purification. Proteomic analysis quantified 216 proteins with statistically different levels of persulfidation in KD cells compared to control adipocytes. In fully differentiated adipocytes, CBS and MPST mRNA and protein levels were abundant, while CTH expression was very low. It is noteworthy that siRNA_MIX administration resulted in a significant decrease in CBS and MPST expression, without impacting on CTH. The combined partial knockdown of the CBS and MPST genes resulted in reduced cellular sulfide levels in parallel to decreased expression of relevant genes for adipocyte biology, including adipogenesis, mitochondrial biogenesis, and lipogenesis, but increased proinflammatory- and senescence-related genes. It should be noted that the combined partial knockdown of CBS and MPST genes also led to a significant disruption in the persulfidation pattern of the adipocyte proteins. Although among the less persulfidated proteins, we identified several relevant proteins for adipocyte adipogenesis and function, among the most persulfidated, key mediators of adipocyte inflammation and dysfunction as well as some proteins that might play a positive role in adipogenesis were found. In conclusion, the current study indicates that the combined partial elimination of CBS and MPST (but not CTH) in adipocytes affects the expression of genes related to the maintenance of adipocyte function and promotes inflammation, possibly by altering the pattern of protein persulfidation in these cells, suggesting that these enzymes were required for the functional maintenance of adipocytes.