Regulation of muscle and metabolic physiology by hypothalamic erythropoietin independently of its peripheral action

A direct effect of the hematocrit on blood glucose: Evidence from hypoxia- and erythropoietin-treated mice

Blood glucose is lower in mountain dwellers living under low partial oxygen pressure. We show that obese mice maintained under hypoxia exhibit a delayed but distinct decrease in blood glucose with improved insulin sensitivity, which is independent of changes in body weight. This effect of hypoxia is mediated by erythropoiesis and is a direct result of the rising hematocrit, which could be due to erythrocytes acting as carriers of glucose units in the blood. Glucose lowering by the red cell mass is evidenced by a prompt decrease in glycemia in mice receiving a blood transfusion. Furthermore, life under hypoxia as well as treatment with erythropoietin reduce glycemia also in mice expressing the erythropoietin receptor exclusively in hematopoietic cells, which contrasts with previous assumptions attributing metabolic actions of erythropoietin to direct action on nonhematopoietic tissues. Our results provide a rationale for associations between hematocrit and blood glucose in humans under anti-anemic therapy, polycythemia, smoking, and high-altitude exposure.

The Role of Erythropoietin in Metabolic Regulation

Erythropoietin (EPO) is a key regulator of erythrocyte production, promoting erythroid progenitor cell survival, division, and differentiation in the fetal liver and adult bone marrow. Mice lacking EPO or its receptor (EPOR) die in utero due to severe anemia. Beyond hematopoiesis, EPO influences non-hematopoietic tissues, including glucose and fat metabolism in adipose tissue, skeletal muscle, and the liver. EPO is used to treat anemia associated with chronic kidney disease clinically and plays a role in maintaining metabolic homeostasis and regulating fat mass. EPO enhances lipolysis while inhibiting lipogenic gene expression in white adipose tissue, brown adipose tissue, skeletal muscle, and the liver, acting through the EPO-EPOR-RUNX1 axis. The non-erythroid EPOR agonist ARA290 also improves diet-induced obesity and glucose tolerance providing evidence for EPO regulation of fat metabolism independent of EPO stimulated erythropoiesis. Therefore, in addition to the primary role of EPO to stimulate erythropoiesis, EPO contributes significantly to EPOR-dependent whole-body metabolic response.

Huaiyu pill alleviates inflammatory bowel disease in mice blocking toll like receptor 4/ myeloid differentiation primary response gene 88/ nuclear factor kappa B subunit 1 pathway

OBJECTIVE

To investigate the therapeutic effects of Huaiyu pill (, HYP) on inflammatory bowel disease (IBD) and the underlying mechanisms have not been elucidated.

METHODS

To establish the IBD model, mice were administered with dextran sulfate sodium (DSS). Mice were intragastrically pre-treated with sulfasalazine (SASP) and HYP. Disease activity index (DAI) and colon length were monitored, and the colonic tissues were subjected to hematoxylin-eosin staining. Pro-inflammatory factors and vascular inflammation-related proteins were determined using enzyme-linked immunosorbent assay (ELISA). The potential mechanisms of HYP were examined using network pharmacology analysis.The expressions of zona occludens 1 (ZO-1), occludin, toll like receptor 4 (TLR4), myeloid differentiation primary response gene 88 (MYD88), and nuclear factor kappa B p65 subunit (NF-κB p65) in colon tissues were examined using Western blotting or immunohistochemical analyses.

RESULTS

Pre-treatment with HYP enhanced the colon length, decreased DAI scores, and mitigated histopathological alterations in DSS-treated mice. HYP alleviated intestinal inflammation by downregulating the levels of interleukin 1 beta (IL-1β), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α) and interleukin 17 (IL-17). Additionally, HYP suppressed the disruption of the gut barrier by upregulating the ZO-1, occludin, and mucin 2 (MUC2) levels and downregulating the endothelin 1 (ET-1) and erythropoietin (EPO) levels. Network pharmacological analysis and experimental results revealed that HYP downregulated the colonic tissue levels of TLR4, MYD88, and NF-κB p65 in DSS-treated mice.

CONCLUSION

This study investigated the in vivotherapeutic effects of HYP on IBD and the underlying molecular mechanisms. These findings provide an experimental foundation for the clinical application of HYP.

Hypothalamic control of energy expenditure and thermogenesis

Energy expenditure and energy intake need to be balanced to maintain proper energy homeostasis. Energy homeostasis is tightly regulated by the central nervous system, and the hypothalamus is the primary center for the regulation of energy balance. The hypothalamus exerts its effect through both humoral and neuronal mechanisms, and each hypothalamic area has a distinct role in the regulation of energy expenditure. Recent studies have advanced the understanding of the molecular regulation of energy expenditure and thermogenesis in the hypothalamus with targeted manipulation techniques of the mouse genome and neuronal function. In this review, we elucidate recent progress in understanding the mechanism of how the hypothalamus affects basal metabolism, modulates physical activity, and adapts to environmental temperature and food intake changes.

The hypothalamus is a key regulator of metabolism, controlling resting metabolism, activity levels, and responses to external temperature and food intake. The balance between energy intake and expenditure must be tightly controlled, with imbalances resulting in metabolic disorders such as obesity or diabetes. Obin Kwon at Seoul National University College of Medicine and Ki Woo Kim at Yonsei University College of Dentistry, Seoul, both in South Korea, and coworkers reviewed how metabolism is regulated by the hypothalamus, a small hormone-producing brain region. They report that hormonal and neuronal signals from the hypothalamus influence the ratio of lean to fatty tissue, gender-based differences in metabolism, activity levels, and weight gain in response to food intake. They note that further studies to untangle cause-and-effect relationships and other genetic factors will improve our understanding of metabolic regulation.

The timeline of neuronal and glial alterations in experimental obesity

In experimental models, hypothalamic dysfunction is a key component of the pathophysiology of diet-induced obesity. Early after the introduction of a high-fat diet, neurons, microglia, astrocytes and tanycytes of the mediobasal hypothalamus undergo structural and functional changes that impact caloric intake, energy expenditure and systemic glucose tolerance. Inflammation has emerged as a central component of this response, and as in other inflammatory conditions, there is a time course of events that determine the fate of distinct cells involved in the central regulation of whole-body energy homeostasis. Here, we review the work that identified key mechanisms, cellular players and temporal features of diet-induced hypothalamic abnormalities.

Erythropoietin Non-hematopoietic Tissue Response and Regulation of Metabolism During Diet Induced Obesity

Erythropoietin (EPO) receptor (EPOR) determines EPO response. High level EPOR on erythroid progenitor cells gives rise to EPO regulated production of red blood cells. Animal models provide evidence for EPO activity in non-hematopoietic tissue mediated by EPOR expression. Beyond erythropoiesis, EPO activity includes neuroprotection in brain ischemia and trauma, endothelial nitric oxide production and cardioprotection, skeletal muscle wound healing, and context dependent bone remodeling affecting bone repair or bone loss. This review highlights examples of EPO protective activity in select non-hematopoietic tissue with emphasis on metabolic response mediated by EPOR expression in fat and brain and sex-specific regulation of fat mass and inflammation associated with diet induced obesity. Endogenous EPO maintains glucose and insulin tolerance and protects against fat mass accumulation and inflammation. Accompanying the increase in erythropoiesis with EPO treatment is improved glucose tolerance and insulin response. During high fat diet feeding, EPO also decreases fat mass accumulation in male mice. The increased white adipose tissue inflammation and macrophage infiltration associated with diet induced obesity are also reduced with EPO treatment with a shift toward an anti-inflammatory state and decreased inflammatory cytokine production. In female mice the protective effect of estrogen against obesity supersedes EPO regulation of fat mass and inflammation, and requires estrogen receptor alpha activity. In brain, EPOR expression in the hypothalamus localizes to proopiomelanocortin neurons in the arcuate nucleus that promotes a lean phenotype. EPO stimulation of proopiomelanocortin neurons increases STAT3 signaling and production of proopiomelanocortin. Cerebral EPO contributes to metabolic response, and elevated brain EPO reduces fat mass and hypothalamus inflammation during diet induced obesity in male mice without affecting EPO stimulated erythropoiesis. Ovariectomy abrogates the sex-specific metabolic response of brain EPO. The sex-dimorphic EPO metabolic response associated with fat mass accumulation and inflammation during diet induced obesity provide evidence for crosstalk between estrogen and EPO in their anti-obesity potential in female mice mediated in part via tissue specific response in brain and white adipose tissue. Endogenous and exogenous EPO response in non-hematopoietic tissue demonstrated in animal models suggests additional activity by which EPO treatment may affect human health beyond increased erythropoiesis.

BDNF corrects NLRP3 inflammasome-induced pyroptosis and glucose metabolism reprogramming through KLF2/HK1 pathway in vascular endothelial cells

NLRP3 inflammasome-mediated vascular EC pyroptosis is a key event in the pathogenesis of atherosclerosis. Dysregulation of glucose metabolism is involved in EC dysfunction. Although BDNF plays a protective role in vascular endothelium physiological activity, the mechanisms underlying this activity are not yet clear. In this study, we investigated the role of BDNF in NLRP3 inflammasome-mediated EC pyroptosis and its associated reprogramming of glucose metabolism. HUVECs were treated with human rBDNF under ox-LDL stimulation. rBDNF alleviated ox-LDL-induced NLRP3 inflammasome formation and HUVEC pyroptosis, as evaluated by NLRP3, caspase1-p10, interleukin-18, and interleukin-1β protein levels, co-localization of NLRP3 and apoptosis-associated speck-like protein, and lactate dehydrogenase release. These effects were prevented by tropomyosin receptor kinase B inhibition and KLF2 silencing. The hyper-activation of glycolysis induced by ox-LDL-induced was mitigated by rBDNF via KLF2 as assessed by glucose uptake, lactate production, and extracellular acidification rate. In addition, the BDNF/KLF2 pathway preserved the mitochondrial membrane potential, intracellular reactive oxygen species generation, electron transport chain processing, oxygen consumption rate, and adenosine triphosphate production. Furthermore, KLF2 interacted with HK1 and HK1 overexpression evoked NLRP3 inflammasome formation. At the clinical level, plasma BDNF and lactate levels were measured in 274 patients who underwent computed tomography and coronary angiography for CAD diagnosis. Patients with CAD had lower BDNF and increased lactate levels than those without CAD. In 94 patients with CAD, circulating BDNF levels were inversely associated with lactate levels. In the receiver operating characteristic analysis of CAD, the areas under the curves for 1/BDNF, lactate, and 1/BDNF+lactate were 0.707, 0.702, and 0.753 respectively. These results indicate that BDNF and lactate are linked in atherosclerotic patients, and BDNF inhibits ox-LDL induced NLRP3 inflammasome formation and pyroptosis in HUVECs via KLF2/HK1-mediated glucose metabolism modulation and mitochondrial homeostasis preservation.