High-Fat Diet-Induced Obesity Alters Dendritic Cell Homeostasis by Enhancing Mitochondrial Fatty Acid Oxidation

NaHS alters synaptic plasticity proteins and enhances dendritic arborization to improve cognitive and motor deficits after traumatic brain injury in mice

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) is a complex medical condition affecting people globally. Hydrogen sulfide (H2S) is a recently discovered gaseous mediator and is dysregulated in the brain after TBI. Sodium hydrogen sulfide (NaHS), a known donor of H2S, is beneficial in various biological processes involving aging and diseases, including injury. It is neuroprotective against oxidative stress, neuroinflammation, and other secondary injury processes. However, the NaHS-H2S system has not been investigated as a regulator of injury-mediated synaptic plasticity proteins and the underlying mechanisms after TBI.

EXPERIMENTAL APPROACH

We developed a model of TBI in Swiss albino mice to study the effects of exogenous H2S, administered as NaHS. We assessed cognitive function (Barnes maze and novel object recognition) and motor function (rotarod). Brain tissue was analysed with ELISA, qRT-PCR, immunoblotting, Golgi-cox staining, and immunofluorescence.

KEY RESULTS

NaHS administration restored the injury-caused decline in H2S levels. Injury-mediated oxidative stress parameters were improved following NaHS. It down-regulated TBI biomarkers, ameliorated the synaptic marker proteins, and improved cognitive and motor deficits. These changes were accompanied by enhanced dendritic arborization and spine number. Restoration of N-methyl D-aspartate receptor subunits and diminished glutamate and calcium levels, along with marked changes in microtubule-associated protein 2 A and calcium/calmodulin-dependent protein kinase II, formed the basis of the underlying mechanism(s).

CONCLUSION AND IMPLICATIONS

Our findings suggest that NaHS could have therapeutic activity against TBI, as it ameliorated cognitive and motor deficits caused by changes in synaptic plasticity proteins and dendritic arborisation, in our model.

Characterization of small RNAs in the spleen of MASH in a non-human primate model

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its advanced stage, metabolic dysfunction-associated steatohepatitis (MASH), are increasingly recognized as a global health issue. This study examines the role of small RNAs in the spleen of MASH using a non-human primate model. We performed high-throughput small RNA sequencing on spleen tissues from MASH-primates, revealing significant alterations in the expression of small non-coding RNAs, especially miRNAs. Notably, miR-96, miR-182, miR-183, and miR-122 showed differential expression in MASH spleens. Predictive and validation studies have identified potential target genes, such as PTX3 and NFIX, that were significantly dysregulated in spleens of MASH. These findings characterized small RNAs in spleen of MASH and offer a novel insight for further research for MASH.

Macrophages and T cells in metabolic disorder-associated cancers

Cancer and metabolic disorders have emerged as major global health challenges, reaching epidemic levels in recent decades. Often viewed as separate issues, metabolic disorders are shown by mounting evidence to heighten cancer risk and incidence. The intricacies underlying this connection are still being unraveled and encompass a complex interplay between metabolites, cancer cells and immune cells within the tumour microenvironment (TME). Here, we outline the interplay between metabolic and immune cell dysfunction in the context of three highly prevalent metabolic disorders, namely obesity; two associated liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH); and type 2 diabetes. We focus primarily on macrophages and T cells, the critical roles of which in dictating inflammatory response and immune surveillance in metabolic disorder-associated cancers are widely reported. Moreover, considering the ever-increasing number of patients prescribed with metabolism disorder-altering drugs and diets in recent years, we discuss how these therapies modulate systemic and local immune phenotypes, consequently impacting cancer malignancy. Collectively, unraveling the determinants of metabolic disorder-associated immune landscape and their role in fuelling cancer malignancy will provide a framework essential to therapeutically address these highly prevalent diseases.

Metabolic regulation of the immune system in health and diseases: mechanisms and interventions

Metabolism, including glycolysis, oxidative phosphorylation, fatty acid oxidation, and other metabolic pathways, impacts the phenotypes and functions of immune cells. The metabolic regulation of the immune system is important in the pathogenesis and progression of numerous diseases, such as cancers, autoimmune diseases and metabolic diseases. The concept of immunometabolism was introduced over a decade ago to elucidate the intricate interplay between metabolism and immunity. The definition of immunometabolism has expanded from chronic low-grade inflammation in metabolic diseases to metabolic reprogramming of immune cells in various diseases. With immunometabolism being proposed and developed, the metabolic regulation of the immune system can be gradually summarized and becomes more and more clearer. In the context of many diseases including cancer, autoimmune diseases, metabolic diseases, and many other disease, metabolic reprogramming occurs in immune cells inducing proinflammatory or anti-inflammatory effects. The phenotypic and functional changes of immune cells caused by metabolic regulation further affect and development of diseases. Based on experimental results, targeting cellular metabolism of immune cells becomes a promising therapy. In this review, we focus on immune cells to introduce their metabolic pathways and metabolic reprogramming, and summarize how these metabolic pathways affect immune effects in the context of diseases. We thoroughly explore targets and treatments based on immunometabolism in existing studies. The challenges of translating experimental results into clinical applications in the field of immunometabolism are also summarized. We believe that a better understanding of immune regulation in health and diseases will improve the management of most diseases.

Adipocyte metabolic state regulates glial phagocytic function

Obesity and type 2 diabetes are well-established risk factors for neurodegenerative disorders1-4, yet the underlying mechanisms remain poorly understood. The adipocyte-brain axis is crucial for brain function, as adipocytes secrete signaling molecules, including lipids and adipokines, that impinge on neural circuits to regulate feeding and energy expenditure5. Disruptions in the adipocyte-brain axis are associated with neurodegenerative conditions6, but the causal links are not fully understood. Neural debris accumulates with age and injury, and glial phagocytic function is crucial for clearing this debris and maintaining a healthy brain microenvironment7-9. Using adult Drosophila, we investigate how adipocyte metabolism influences glial phagocytic activity in the brain. We demonstrate that a prolonged obesogenic diet increases adipocyte fatty acid oxidation and ketogenesis. Genetic manipulations that mimic obesogenic diet-induced changes in adipocyte lipid and mitochondrial metabolism unexpectedly reduce the expression of the phagocytic receptor Draper in Drosophila microglia-like cells in the brain. We identify Apolpp-the Drosophila equivalent of human apolipoprotein B (ApoB)-as a critical adipocyte-derived signal that regulates glial phagocytosis. Additionally, we show that Lipoprotein Receptor 1 (LpR1), the LDL receptor on phagocytic glia, is required for glial capacity to clear injury-induced neuronal debris. Our findings establish that adipocyte-brain lipoprotein signaling regulates glial phagocytic function, revealing a novel pathway that links adipocyte metabolic disorders with neurodegeneration.

Obesity-induced chronic low-grade inflammation in adipose tissue: A pathway to Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of cognitive impairment worldwide. Overweight and obesity are strongly associated with comorbidities, such as hypertension, diabetes, and insulin resistance (IR), which contribute substantially to the development of AD and subsequent morbidity and mortality. Adipose tissue (AT) is a highly dynamic organ composed of a diverse array of cell types, which can be classified based on their anatomic localization or cellular composition. The expansion and remodeling of AT in the context of obesity involves immunometabolic and functional shifts steered by the intertwined actions of multiple immune cells and cytokine signaling within AT, which contribute to the development of metabolic disorders, IR, and systemic markers of chronic low-grade inflammation. Chronic low-grade inflammation, a prolonged, low-dose stimulation by specific immunogens that can progress from localized sites and affect multiple organs throughout the body, leads to neurodystrophy, increased apoptosis, and disruption of homeostasis, manifesting as brain atrophy and AD-related pathology. In this review, we sought to elucidate the mechanisms by which AT contributes to the onset and progression of AD in obesity through the mediation of chronic low-grade inflammation, particularly focusing on the roles of adipokines and AT-resident immune cells.

Histone demethylase JARID1C/KDM5C regulates Th17 cells by increasing IL-6 expression in diabetic plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are first responders to tissue injury, where they prime naive T cells. The role of pDCs in physiologic wound repair has been examined, but little is known about pDCs in diabetic wound tissue and their interactions with naive CD4+ T cells. Diabetic wounds are characterized by increased levels of inflammatory IL-17A cytokine, partly due to increased Th17 CD4+ cells. This increased IL-17A cytokine, in excess, impairs tissue repair. Here, using human tissue and murine wound healing models, we found that diabetic wound pDCs produced excess IL-6 and TGF-β and that these cytokines skewed naive CD4+ T cells toward a Th17 inflammatory phenotype following cutaneous injury. Further, we identified that increased IL-6 cytokine production by diabetic wound pDCs is regulated by a histone demethylase, Jumonji AT-rich interactive domain 1C histone demethylase (JARID1C). Decreased JARID1C increased IL-6 transcription in diabetic pDCs, and this process was regulated upstream by an IFN-I/TYK2/JAK1,3 signaling pathway. When inhibited in nondiabetic wound pDCs, JARID1C skewed naive CD4+ T cells toward a Th17 phenotype and increased IL-17A production. Together, this suggests that diabetic wound pDCs are epigenetically altered to increase IL-6 expression that then affects T cell phenotype. These findings identify a therapeutically manipulable pathway in diabetic wounds.

Reduced Branched-Chain Amino Acid Intake Improved High-Fat Diet-Induced Nonalcoholic Fatty Pancreas Disease in Mice

OBJECTIVE

To explore the effects of branched-chain amino acids (BCAAs) on nonalcoholic fatty pancreas disease (NAFPD) and its possible mechanism in high-fat diet (HFD) induced mice.

MATERIALS AND METHODS

Pancreatic morphology and lipid infiltration was assessed by hematoxylin-eosin staining and immunohistochemistry, and lipid levels in the pancreas were determined using colorimetric enzymatic method. Relevant mechanism was investigated using western blotting and biochemical test.

RESULTS

In HFD-fed mice, dietary BCAAs restriction could attenuate body weight increase, improve glucose metabolism, and reduce excessive lipid accumulation in the pancreas. Furthermore, expression of AMPKα and downstream uncoupling protein 1 were upregulated, while genes related to mammalian target of rapamycin complex 1 (mTORC1) signal pathway and lipid de novo synthesis were suppressed in HFD-BCAA restriction group compared with HFD and HFD-high BCAAs fed mice. In addition, BCAA restriction upregulated expression of BCAAs related metabolic enzymes including PPM1K and BCKDHA, and decreased the levels of BCAAs and branched chain keto acid in the pancreas. However, there was no difference in levels of lipid content in the pancreas and gene expression of AMPKα and mTORC1 between HFD and HFD-high BCAAs groups.

CONCLUSIONS

Branched-chain amino acid restriction ameliorated HFD-induced NAFPD in mice by activation of AMPKα pathway and suppression of mTORC1 pathway.

Sexual dimorphism of osteoclast reliance on mitochondrial oxidation of energy substrates in the mouse

Osteoclasts specialize in bone resorption and are critical for bone remodeling. Previous studies have shown that osteoclasts possess abundant mitochondria and derive most energy through oxidative phosphorylation (OXPHOS). However, the energy substrates fueling OXPHOS in osteoclasts remain to be fully defined. Here, we showed that osteoclast differentiation was coupled with increased oxidation of glucose, glutamine, and oleate. Transcriptomic analyses with RNA sequencing revealed marked upregulation of genes participating in OXPHOS and mitochondrial fatty acid oxidation, during osteoclast differentiation. Increased mitochondrial oxidation of long-chain fatty acids was required for osteoclast differentiation in vitro. However, blocking fatty acid oxidation in vivo, by deletion of carnitine palmitoyltransferase 1a (Cpt1a) in osteoclast progenitors, impaired osteoclast formation only in the female mice. The Cpt1a-deficient females were further protected from osteoclast activation by a high-fat diet. The males, on the contrary, exhibited normal bone resorption despite Cpt1a deletion, regardless of the dietary fat content. Moreover, concurrent deletion of mitochondrial pyruvate carrier 1 and Cpt1a, blocking mitochondrial oxidation of both glucose and fatty acids in the osteoclast lineage, failed to impede bone resorption in the males. The study therefore uncovers a female-specific dependence on mitochondrial oxidation of fatty acids and glucose in osteoclasts in vivo.

Dietary fat and lipid metabolism in the tumor microenvironment

Metabolic reprogramming has been considered a core hallmark of cancer, in which excessive accumulation of lipids promote cancer initiation, progression and metastasis. Lipid metabolism often includes the digestion and absorption of dietary fat, and the ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment. Among multiple cancer risk factors, obesity has a positive association with multiple cancer types, while diets like calorie restriction and fasting improve health and delay cancer. Impact of these diets on tumorigenesis or cancer prevention are generally studied on cancer cells, despite heterogeneity of the tumor microenvironment. Cancer cells regularly interact with these heterogeneous microenvironmental components, including immune and stromal cells, to promote cancer progression and metastasis, and there is an intricate metabolic crosstalk between these compartments. Here, we focus on discussing fat metabolism and response to dietary fat in the tumor microenvironment, focusing on both immune and stromal components and shedding light on therapeutic strategies surrounding lipid metabolic and signaling pathways.

Immunometabolism of dendritic cells in health and disease

Dendritic cells (DCs) are crucial mediators that bridge the innate and adaptive immune responses. Cellular rewiring of metabolism is an emerging regulator of the activation, migration, and functional specialization of DC subsets in specific microenvironments and immunological conditions. DCs undergo metabolic adaptation to exert immunogenic or tolerogenic effects in different contexts. Also, beyond their intracellular metabolic and signaling roles, metabolites and nutrients mediate the intercellular crosstalk between DCs and other cell types, and such crosstalk orchestrates DC function and immune responses. Here, we provide a comprehensive review of the metabolic regulation of DC biology in various contexts and summarize the current understanding of such regulation in directing immune homeostasis and inflammation, specifically with respect to infections, autoimmunity, tolerance, cancer, metabolic diseases, and crosstalk with gut microbes. Understanding context-specific metabolic alterations in DCs may identify mechanisms for physiological and pathological functions of DCs and yield potential opportunities for therapeutic targeting of DC metabolism in many diseases.

Neuroinflammation: A Modifiable Pathway Linking Obesity, Alzheimer's disease, and Depression

Obesity, depression and Alzheimer's disease (AD) are three major interrelated modern health conditions with complex relationships. Early-life depression may serve as a risk factor for AD, while late-life depression may be a prodrome of AD. Depression affects approximately 23% of obese individuals, and depression itself raises the risk of obesity by 37%. Mid-life obesity independently increases AD risk, while late-life obesity, particularly metabolically healthy obesity, may offer protection against AD pathology. Chronic inflammation serves as a key mechanism linking obesity, AD, and depression, encompassing systemic inflammation from metabolic disturbances, immune dysregulation through the gut microbiome, and direct interactions with amyloid pathology and neuroinflammation. In this review, we explore the biological mechanisms of neuroinflammation in relation to obesity, AD, and depression. We assess the efficacy of therapeutic interventions targeting neuroinflammation and discuss current and future radiological imaging initiatives for studying neuroinflammation. By comprehending the intricate interplay among depression, obesity, and AD, especially the role of neuroinflammation, we can advance our understanding and develop innovative strategies for prevention and treatment.

Lipid Metabolism Reprogramming of Immune Cells in Acne: An Update

Acne vulgaris is one of the most widespread skin conditions and the main reason for visiting a dermatologist. Inflammatory response and abnormal infiltrations of immune cells are the main pathogenesis of acne. The increased lipid is the prerequisite for the acne, and the perturbation of lipid composition and content is consistent with the severity of acne. Furthermore, the increased lipid production not only contributes to the occurrence and development of acne, but also sensitizes the function of immune cells. The lipid metabolic dysfunction aggravates the severity of local tissue and provides pro-inflammatory-cytokine cues, which indicates the crucial roles of lipid metabolism on immune cells. Recent advances have demonstrated the lipid metabolism reprogramming of various immune cells in acne lesion. The abnormal lipid accumulation, lipolysis, and fatty acid oxidation lead to the activation and differentiation of immune cells, which promotes the pro-inflammatory cytokines production. Thus, this review discusses the emerging role of lipid metabolism reprogramming of immune cells in the progress of acne and aims to constitute food for others' projects involved in acne research.

Lipid metabolism in dendritic cell biology

Dendritic cells (DCs) are innate immune cells that detect and process environmental signals and communicate them with T cells to bridge innate and adaptive immunity. Immune signals and microenvironmental cues shape the function of DC subsets in different contexts, which is associated with reprogramming of cellular metabolic pathways. In addition to integrating these extracellular cues to meet bioenergetic and biosynthetic demands, cellular metabolism interplays with immune signaling to shape DC-dependent immune responses. Emerging evidence indicates that lipid metabolism serves as a key regulator of DC responses. Here, we summarize the roles of fatty acid and cholesterol metabolism, as well as selective metabolites, in orchestrating the functions of DCs. Specifically, we highlight how different lipid metabolic programs, including de novo fatty acid synthesis, fatty acid β oxidation, lipid storage, and cholesterol efflux, influence DC function in different contexts. Further, we discuss how dysregulation of lipid metabolism shapes DC intracellular signaling and contributes to the impaired DC function in the tumor microenvironment. Finally, we conclude with a discussion on key future directions for the regulation of DC biology by lipid metabolism. Insights into the connections between lipid metabolism and DC functional specialization may facilitate the development of new therapeutic strategies for human diseases.

Immunometabolism at the Heart of Cardiovascular Disease

Immune cell function among the myocardium, now more than ever, is appreciated to regulate cardiac function and pathophysiology. This is the case for both innate immunity, which includes neutrophils, monocytes, dendritic cells, and macrophages, as well as adaptive immunity, which includes T cells and B cells. This function is fueled by cell-intrinsic shifts in metabolism, such as glycolysis and oxidative phosphorylation, as well as metabolite availability, which originates from the surrounding extracellular milieu and varies during ischemia and metabolic syndrome. Immune cell crosstalk with cardiac parenchymal cells, such as cardiomyocytes and fibroblasts, is also regulated by complex cellular metabolic circuits. Although our understanding of immunometabolism has advanced rapidly over the past decade, in part through valuable insights made in cultured cells, there remains much to learn about contributions of in vivo immunometabolism and directly within the myocardium. Insight into such fundamental cell and molecular mechanisms holds potential to inform interventions that shift the balance of immunometabolism from maladaptive to cardioprotective and potentially even regenerative. Herein, we review our current working understanding of immunometabolism, specifically in the settings of sterile ischemic cardiac injury or cardiometabolic disease, both of which contribute to the onset of heart failure. We also discuss current gaps in knowledge in this context and therapeutic implications.

Reshaping immunometabolism in the tumour microenvironment to improve cancer immunotherapy

The evolving understanding of cellular metabolism has revealed a the promise of strategies aiming to modulate anticancer immunity by targeting metabolism. The combination of metabolic inhibitors with immune checkpoint blockade (ICB), chemotherapy and radiotherapy may offer new approaches to cancer treatment. However, it remains unclear how these strategies can be better utilized despite the complex tumour microenvironment (TME). Oncogene-driven metabolic changes in tumour cells can affect the TME, limiting the immune response and creating many barriers to cancer immunotherapy. These changes also reveal opportunities to reshape the TME to restore immunity by targeting metabolic pathways. Further exploration is required to determine how to make better use of these mechanistic targets. Here, we review the mechanisms by which tumour cells reshape the TME and cause immune cells to transition into an abnormal state by secreting multiple factors, with the ultimate goal of proposing targets and optimizing the use of metabolic inhibitors. Deepening our understanding of changes in metabolism and immune function in the TME will help advance this promising field and enhance immunotherapy.

Diverse effects of obesity on antitumor immunity and immunotherapy

Currently, obesity is one of the biggest health burdens facing society because it causes several comorbidities, such as type 2 diabetes, atherosclerosis, and heart disease. Obesity is also linked to multiple types of cancer. Obesity is the second most common preventable cause of cancer after smoking; the rates of obesity are increasing worldwide, as are the rates of obesity-associated cancer. Multiple factors link obesity to cancer, such as increased levels of growth hormones and adipokines, gut dysbiosis, altered tumor metabolism, and chronic low-grade inflammation. More recently, obesity has been shown to also affect the immune response against cancer. In this review we discuss the interplay between obesity, the immune system, and cancer.

Tumor Microenvironment and Metabolism: Role of the Mitochondrial Melatonergic Pathway in Determining Intercellular Interactions in a New Dynamic Homeostasis

There is a growing interest in the role of alterations in mitochondrial metabolism in the pathoetiology and pathophysiology of cancers, including within the array of diverse cells that can form a given tumor microenvironment. The 'exhaustion' in natural killer cells and CD8+ t cells as well as the tolerogenic nature of dendritic cells in the tumor microenvironment seems determined by variations in mitochondrial function. Recent work has highlighted the important role played by the melatonergic pathway in optimizing mitochondrial function, limiting ROS production, endogenous antioxidants upregulation and consequent impacts of mitochondrial ROS on ROS-dependent microRNAs, thereby impacting on patterned gene expression. Within the tumor microenvironment, the tumor, in a quest for survival, seeks to 'dominate' the dynamic intercellular interactions by limiting the capacity of cells to optimally function, via the regulation of their mitochondrial melatonergic pathway. One aspect of this is the tumor's upregulation of kynurenine and the activation of the aryl hydrocarbon receptor, which acts to metabolize melatonin and increase the N-acetylserotonin/melatonin ratio, with effluxed N-acetylserotonin acting as a brain-derived neurotrophic factor (BDNF) mimic via its activation of the BDNF receptor, TrkB, thereby increasing the survival and proliferation of tumors and cancer stem-like cells. This article highlights how many of the known regulators of cells in the tumor microenvironment can be downstream of the mitochondrial melatonergic pathway regulation. Future research and treatment implications are indicated.