Multifaceted mitochondrial quality control in brown adipose tissue

Intercellular Mitochondrial transfer: Therapeutic implications for energy metabolism in heart failure

Heart failure (HF) remains one of the leading causes of high morbidity and mortality globally. Impaired cardiac energy metabolism plays a critical role in the pathological progression of HF. Various forms of HF exhibit marked differences in energy metabolism, particularly in mitochondrial function and substrate utilization. Recent studies have increasingly highlighted that improving energy metabolism in HF patients as a crucial treatment strategy. Mitochondrial transfer is emerging as a promising and precisely regulated therapeutic strategy for treating metabolic disorders. This paper specifically reviews the characteristics of mitochondrial energy metabolism across different types of HF and explores the modes and mechanisms of mitochondrial transfer between different cell types in the heart, such as cardiomyocytes, fibroblasts, and immune cells. We focused on the therapeutic potential of intercellular mitochondrial transfer in improving energy metabolism disorders in HF. We also discuss the role of signal transduction in mitochondrial transfer, highlighting that mitochondria not only function as energy factories but also play crucial roles in intercellular communication, metabolic regulation, and tissue repair. This study provides new insights into improving energy metabolism in heart failure patients and proposes promising new therapeutic strategies.

Transfer and fates of damaged mitochondria: role in health and disease

Intercellular communication is pivotal in mediating the transfer of mitochondria from donor to recipient cells. This process orchestrates various biological functions, including tissue repair, cell proliferation, differentiation and cancer invasion. Typically, dysfunctional and depolarized mitochondria are eliminated through intracellular or extracellular pathways. Nevertheless, increasing evidence suggests that intercellular transfer of damaged mitochondria is associated with the pathogenesis of diverse diseases. This review investigates the prevalent triggers of mitochondrial damage and the underlying mechanisms of mitochondrial transfer, and elucidates the role of directional mitochondrial transfer in both physiological and pathological contexts. Additionally, we propose potential previously unknown mechanisms mediating mitochondrial transfer and explore their prospective roles in disease prevention and therapy.

Discussion on the treatment of diabetic kidney disease based on the "gut-fat-kidney" axis

Diabetic kidney disease is the main cause of end-stage renal disease, and its prevention and treatment are still a major clinical problem. The human intestine has a complex flora of hundreds of millions of microorganisms, and intestinal microorganisms, and their derivatives are closely related to renal inflammatory response, immune response, and material metabolism. Brown adipose tissue is the main part of adaptive thermogenesis. Recent studies have shown that activating brown fat by regulating intestinal flora has good curative effects in diabetic kidney disease-related diseases. As an emerging medical concept, the "gut-fat-kidney" axis has received increasing attention in diabetic kidney disease and related diseases. However, the specific mechanism involved needs further study. A new theoretical basis for the prevention and treatment of diabetic kidney disease is presented in this article, based on the "gut-fat-kidney" axis.

Taraxacum Mongolicum Polysaccharides Reverses Mice Obesity via Activation of AKT/mTOR Pathway

BACKGROUND/OBJECTIVES

The global prevalence of obesity and its associated health complications represent significant public health concerns. Plant polysaccharides have been demonstrated to possess a range of beneficial pharmacological effects. This experiment was designed to elucidate the mechanisms of dietary Taraxacum mongolicum polysaccharides involved in the regulation of obesity and fat browning.

METHODS

Male C57BL/6J mice were randomly divided into three groups: a control group, a high-fat diet (HFD) group, and an HFD group supplemented with 0.3% TMPs. The mice were fed their respective diets for 10 weeks, after which their body weight, food consumption, and serum lipid levels were measured. Histological analysis was performed to assess lipid deposition in adipose tissue and liver. Western blot was used to assess the expression of proteins involved in the AKT/mTOR pathway.

RESULTS

The results show that compared with the HFD group, the TMP supplementation group's body-weight gain (12.17 ± 1.77) significantly decreased. TMPs also reduced serum levels of total cholesterol, triglycerides, and low-density lipoprotein cholesterol. Histological analysis showed that TMPs reduced lipid deposition in both adipose tissue and the liver.

CONCLUSIONS

In addition, TMPs increased the expression of phosphorylated AKT and the mechanistic target of rapamycin (mTOR), indicating that TMPs exert their beneficial effects on lipid metabolism via the AKT/mTOR pathway.

Irisin Protects Musculoskeletal Homeostasis via a Mitochondrial Quality Control Mechanism

Irisin, a myokine derived from fibronectin type III domain-containing 5 (FNDC5), is increasingly recognized for its protective role in musculoskeletal health through the modulation of mitochondrial quality control. This review synthesizes the current understanding of irisin's impact on mitochondrial biogenesis, dynamics, and autophagy in skeletal muscle, elucidating its capacity to bolster muscle strength, endurance, and resilience against oxidative-stress-induced muscle atrophy. The multifunctional nature of irisin extends to bone metabolism, where it promotes osteoblast proliferation and differentiation, offering a potential intervention for osteoporosis and other musculoskeletal disorders. Mitochondrial quality control is vital for cellular metabolism, particularly in energy-demanding tissues. Irisin's influence on this process is highlighted, suggesting its integral role in maintaining cellular homeostasis. The review also touches upon the regulatory mechanisms of irisin secretion, predominantly induced by exercise, and its systemic effects as an endocrine factor. While the therapeutic potential of irisin is promising, the need for standardized measurement techniques and further elucidation of its mechanisms in humans is acknowledged. The collective findings underscore the burgeoning interest in irisin as a keystone in musculoskeletal health and a candidate for future therapeutic strategies.

Lipid-associated macrophages reshape BAT cell identity in obesity

Obesity and type 2 diabetes cause a loss in brown adipose tissue (BAT) activity, but the molecular mechanisms that drive BAT cell remodeling remain largely unexplored. Using a multilayered approach, we comprehensively mapped a reorganization in BAT cells. We uncovered a subset of macrophages as lipid-associated macrophages (LAMs), which were massively increased in genetic and dietary model of BAT expansion. LAMs participate in this scenario by capturing extracellular vesicles carrying damaged lipids and mitochondria released from metabolically stressed brown adipocytes. CD36 scavenger receptor drove LAM phenotype, and CD36-deficient LAMs were able to increase brown fat genes in adipocytes. LAMs released transforming growth factor β1 (TGF-β1), which promoted the loss of brown adipocyte identity through aldehyde dehydrogenase 1 family member A1 (Aldh1a1) induction. These findings unfold cell dynamic changes in BAT during obesity and identify LAMs as key responders to tissue metabolic stress and drivers of loss of brown adipocyte identity.

Hydrogen Gas Inhalation Treatment for Coronary Artery Lesions in a Kawasaki Disease Mouse Model

BACKGROUND

Kawasaki disease (KD) is a syndrome primarily affecting young children, typically under the age of five, and is characterized by the development of acute vasculitis. Through extensive research conducted on both murine and human subjects, it has been demonstrated that heightened levels of reactive oxygen species (ROS) play a pivotal role in the development of KD, especial coronary artery lesions (CALs). Hydrogen gas exhibits potent antioxidant properties that effectively regulate ROS production and the inflammatory response.

METHODS

We used Lactobacillus casei cell wall extract (LCWE)-induced vasculitis in mice as an animal model of KD and treated the mice with hydrogen gas inhalation.

RESULTS

We observed significant dilatation and higher Z scores in the left coronary artery (LCA) in D21 and D28 in mice after LCWE treatment compared to the control group (p < 0.001) and a significant resolution of LCA diameters (p < 0.01) and Z scores (p < 0.01) after treatment with inhaled hydrogen gas. We further demonstrated that serum IL-6 expression was higher in mice after LCWE treatment (p < 0.01) and IL-6 significantly decreased after inhaled hydrogen gas therapy (p < 0.001).

CONCLUSION

According to our literature review, this is the first report where hydrogen gas inhalation has been demonstrated to be effective for the treatment of coronary artery dilatation in a KD murine model.

Myostatin regulates energy homeostasis through autocrine- and paracrine-mediated microenvironment communication

Myostatin (MSTN) has long been recognized as a critical regulator of muscle mass. Recently, there has been increasing interest in its role in metabolism. In our study, we specifically knocked out MSTN in brown adipose tissue (BAT) from mice (MSTNΔUCP1) and found that the mice gained more weight than did controls when fed a high-fat diet, with progressive hepatosteatosis and impaired skeletal muscle activity. RNA-Seq analysis indicated signatures of mitochondrial dysfunction and inflammation in the MSTN-ablated BAT. Further studies demonstrated that Kruppel-like factor 4 (KLF4) was responsible for the metabolic phenotypes observed, whereas fibroblast growth factor 21 (FGF21) contributed to the microenvironment communication between adipocytes and macrophages induced by the loss of MSTN. Moreover, the MSTN/SMAD2/3-p38 signaling pathway mediated the expression of KLF4 and FGF21 in adipocytes. In summary, our findings suggest that brown adipocyte-derived MSTN regulated BAT thermogenesis via autocrine and paracrine effects on adipocytes or macrophages, ultimately regulating systemic energy homeostasis.

Dynamic changes of immunocyte subpopulations in thermogenic activation of adipose tissues

Objectives

The effects of cold exposure on whole-body metabolism in humans have gained increasing attention. Brown or beige adipose tissues are crucial in cold-induced thermogenesis to dissipate energy and thus have the potential to combat metabolic disorders. Despite the immune regulation of thermogenic adipose tissues, the overall changes in vital immune cells during distinct cold periods remain elusive. This study aimed to discuss the overall changes in immune cells under different cold exposure periods and to screen several potential immune cell subpopulations on thermogenic regulation.

Methods

Cibersort and mMCP-counter algorithms were employed to analyze immune infiltration in two (brown and beige) thermogenic adipose tissues under distinct cold periods. Changes in some crucial immune cell populations were validated by reanalyzing the single-cell sequencing dataset (GSE207706). Flow cytometry, immunofluorescence, and quantitative real-time PCR assays were performed to detect the proportion or expression changes in mouse immune cells of thermogenic adipose tissues under cold challenge.

Results

The proportion of monocytes, naïve, and memory T cells increased, while the proportion of NK cells decreased under cold exposure in brown adipose tissues.

Conclusion

Our study revealed dynamic changes in immune cell profiles in thermogenic adipose tissues and identified several novel immune cell subpopulations, which may contribute to thermogenic activation of adipose tissues under cold exposure.

The molecular mechanism of macrophage-adipocyte crosstalk in maintaining energy homeostasis

Interactions between macrophages and adipocytes in adipose tissue are critical for the regulation of energy metabolism and obesity. Macrophage polarization induced by cold or other stimulations can drive metabolic reprogramming of adipocytes, browning, and thermogenesis. Accordingly, investigating the roles of macrophages and adipocytes in the maintenance of energy homeostasis is critical for the development of novel therapeutic approaches specifically targeting macrophages in metabolic disorders such as obesity. Current review outlines macrophage polarization not only regulates the release of central nervous system and inflammatory factors, but controls mitochondrial function, and other factor that induce metabolic reprogramming of adipocytes and maintain energy homeostasis. We also emphasized on how the adipocytes conversely motivate the polarization of macrophage. Exploring the interactions between adipocytes and macrophages may provide new therapeutic strategies for the management of obesity-related metabolic diseases.

Xiasangju alleviate metabolic syndrome by enhancing noradrenaline biosynthesis and activating brown adipose tissue

Metabolic syndrome (MetS) is a clinical condition associated with multiple metabolic risk factors leading to type 2 diabetes mellitus and other metabolic diseases. Recent evidence suggests that modulating adipose tissue to adaptive thermogenesis may offer therapeutic potential for MetS. Xiasangju (XSJ) is a marketed drug and dietary supplement used for the treatment of metabolic disease with anti-inflammatory activity. This study investigated the therapeutic effects of XSJ and the underlying mechanisms affecting the activation of brown adipose tissue (BAT) in MetS. The results revealed that XSJ ameliorated MetS by enhancing glucose and lipid metabolism, leading to reduced body weight and abdominal circumference, decreased adipose tissue and liver index, and improved blood glucose tolerance. XSJ administration stimulated catecholamine biosynthesis, increasing noradrenaline (NA) levels and activating NA-mediated proteins in BAT. Thus, BAT enhanced thermogenesis and oxidative phosphorylation (OXPHOS). Moreover, XSJ induced changes in gut microbiota composition, with an increase in Oscillibacter abundance and a decrease in Bilophila, Candidatus Stoquefichus, Holdemania, Parasutterella and Rothia. XSJ upregulated the proteins associated with intestinal tight junctions corresponding with lower serum lipopolysaccharide (LPS), tumor necrosis factor α (TNF-α) monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) levels to maintain NA signaling transport. In summary, XSJ may alleviate MetS by promoting thermogenesis in BAT to ultimately boost energy metabolism through increasing NA biosynthesis, strengthening intestinal barrier integrity and reducing low-grade inflammation. These findings suggest XSJ has potential as a natural therapeutic agent for the treatment of MetS.

Deciphering the relationship between temperature and immunity

Fever is a hallmark symptom of disease across the animal kingdom. Yet, despite the evidence linking temperature fluctuation and immune response, much remains to be discovered about the molecular mechanisms governing these interactions. In patients with rheumatoid arthritis, for instance, it is clinically accepted that joint temperature can predict disease progression. But it was only recently demonstrated that the mitochondria of stimulated T cells can rise to an extreme 50°C, potentially indicating a cellular source of these localized 'fevers'. A challenge to dissecting these mechanisms is a bidirectional interplay between temperature and immunity. Heat shock response is found in virtually all organisms, activating protective pathways when cells are exposed to elevated temperatures. However, the temperature threshold that activates these pathways can vary within the same organism, with human immune cells, in particular, demonstrating differential sensitivity to heat. Such inter-cellular variation may be clinically relevant given the small but significant temperature differences seen between tissues, ages, and sexes. Greater understanding of how such small temperature perturbations mediate immune responses may provide new explanations for persistent questions in disease such as sex disparity in disease prevalence. Notably, the prevalence and severity of many maladies are rising with climate change, suggesting temperature fluctuations can interact with disease on multiple levels. As global temperatures are rising, and our body temperatures are falling, questions regarding temperature-immune interactions are increasingly critical. Here, we review this aspect of environmental interplay to better understand temperature's role in immune variation and subsequent risk of disease.

GPR84-mediated signal transduction affects metabolic function by promoting brown adipocyte activity

The G protein-coupled receptor 84 (GPR84), a medium-chain fatty acid receptor, has garnered attention because of its potential involvement in a range of metabolic conditions. However, the precise mechanisms underlying this effect remain elusive. Our study has shed light on the pivotal role of GPR84, revealing its robust expression and functional significance within brown adipose tissue (BAT). Mice lacking GPR84 exhibited increased lipid accumulation in BAT, rendering them more susceptible to cold exposure and displaying reduced BAT activity compared with their WT counterparts. Our in vitro experiments with primary brown adipocytes from GPR84-KO mice revealed diminished expression of thermogenic genes and reduced O2 consumption. Furthermore, the application of the GPR84 agonist 6-n-octylaminouracil (6-OAU) counteracted these effects, effectively reinstating the brown adipocyte activity. These compelling in vivo and in vitro findings converge to highlight mitochondrial dysfunction as the primary cause of BAT anomalies in GPR84-KO mice. The activation of GPR84 induced an increase in intracellular Ca2+ levels, which intricately influenced mitochondrial respiration. By modulating mitochondrial Ca2+ levels and respiration, GPR84 acts as a potent molecule involved in BAT activity. These findings suggest that GPR84 is a potential therapeutic target for invigorating BAT and ameliorating metabolic disorders.

Fundamental and Applicative Aspects of the Unfolded Protein Response in Yeasts

Upon the dysfunction or functional shortage of the endoplasmic reticulum (ER), namely, ER stress, eukaryotic cells commonly provoke a protective gene expression program called the unfolded protein response (UPR). The molecular mechanism of UPR has been uncovered through frontier genetic studies using Saccharomyces cerevisiae as a model organism. Ire1 is an ER-located transmembrane protein that directly senses ER stress and is activated as an RNase. During ER stress, Ire1 promotes the splicing of HAC1 mRNA, which is then translated into a transcription factor that induces the expression of various genes, including those encoding ER-located molecular chaperones and protein modification enzymes. While this mainstream intracellular UPR signaling pathway was elucidated in the 1990s, new intriguing insights have been gained up to now. For instance, various additional factors allow UPR evocation strictly in response to ER stress. The UPR machineries in other yeasts and fungi, including pathogenic species, are another important research topic. Moreover, industrially beneficial yeast strains carrying an enforced and enlarged ER have been produced through the artificial and constitutive induction of the UPR. In this article, we review canonical and up-to-date insights concerning the yeast UPR, mainly from the viewpoint of the functions and regulation of Ire1 and HAC1.

The Emerging Importance of Mitochondria in White Adipocytes: Neither Last nor Least

The growing recognition of mitochondria's crucial role in the regulation of white adipose tissue remodeling and energy balance underscores its significance. The marked metabolic diversity of mitochondria provides the molecular and cellular foundation for enabling adipose tissue plasticity in response to various metabolic cues. Effective control of mitochondrial function at the cellular level, not only in thermogenic brown and beige adipocytes but also in energy-storing white adipocytes, exerts a profound influence on adipose homeostasis. Furthermore, mitochondria play a pivotal role in intercellular communication within adipose tissue via production of metabolites with signaling properties. A more comprehensive understanding of mitochondrial regulation within white adipocytes will empower the development of targeted and efficacious strategies to enhance adipose function, leading to advancements in overall metabolic health.