Systemic Insulin Sensitivity Research Articles

Repetitive transcranial magnetic stimulation elicits weight loss and improved insulin sensitivity in type 2 diabetic rats.

Type 2 diabetes (T2D) accounts for the majority of diabetes incidences and remains a widespread global chronic disorder. Apart from early lifestyle changes, intervention options for T2D are mainly pharmaceutical. Repetitive transcranial magnetic stimulation (rTMS) has been approved by the FDA as a therapeutic intervention option for major depressive disorders, with further studies also indicating its role in energy metabolism and appetite. Considering its safe and non-invasive properties, we evaluated the effects of rTMS on systemic metabolism using T2D rats. We observed that rTMS improved glucose tolerance and insulin sensitivity in T2D rats after a 10-day exposure. Improved systemic insulin sensitivity was maintained after a 21-day treatment period, accompanied by modest yet significant weight loss. Circulating serum lipid levels, including those of cholesteryl ester, tryglyceride and ceramides, were also reduced following rTMS application. RNA-seq analyses further revealed a changed expression profile of hepatic genes that are related to sterol production and fatty acid metabolism. Altered expression of hypothalamic genes that are related to appetite regulation, neural activity and ether lipid metabolism were also implicated. In summary, our data report a positive impact of rTMS on systemic insulin sensitivity and weight management of T2D rats. The underlying mechanisms via which rTMS regulates systemic metabolic parameters partially involve lipid utilization in the periphery as well as central regulation of energy intake and lipid metabolism.

7624 m6A mRNA Methylation in Brown Adipose Tissue Regulates Systemic Insulin Sensitivity via an Inter-Organ Prostaglandin Signaling Axis

Abstract Disclosure: L. Xiao: None. D. F De Jesus: None. C. Ju: None. J. Wei: None. J. Hu: None. A. DiStefano-Forti: None. T. Tsuji: None. C. Cero: None. V. Männistö: None. S.M. Manninen: None. S. Wei: None. O. Ijaduola: None. M. Blüher: Consulting Fee; Self; Amgen Inc, AstraZeneca, Bayer, Inc., Boehringer Ingelheim, Lilly USA, LLC, Novo Nordisk, Pfizer, Inc., Sanofi. A.M. Cypess: None. J. Pihlajamäki: None. Y. Tseng: None. C. He: Advisory Board Member; Self; Accent Therapeutics. R.N. Kulkarni: Advisory Board Member; Self; Novo Nordisk, Biomea, Inversago, REDD. Brown adipose tissue (BAT) has the capacity to regulate systemic metabolism through the secretion of “Batokines” including signaling lipids. N6-methyladenosine (m6A) is the most prevalent and abundant post-transcriptional mRNA modification and has been reported to regulate BAT adipogenesis and energy expenditure. Here, we demonstrate that the absence of the m6A writer, methyltransferase-like 14 (METTL14), modifies the BAT secretome to initiate inter-organ communication to improve systemic insulin sensitivity. Importantly, these phenotypes are independent of UCP1-mediated energy expenditure and thermogenesis. Using lipidomics, we identified prostaglandin E2 (PGE2) and prostaglandin F2a (PGF2a) as M14KO-BAT-secreted insulin sensitizers. Notably, circulatory PGE2 and PGF2a levels are inversely correlated with insulin sensitivity in humans. Furthermore, in vivo administration of PGE2 and PGF2a in high-fat diet-induced insulin-resistant obese mice recapitulates the phenotypes of Mettl14-deficient animals. PGE2 or PGF2a improves insulin signaling by suppressing the expression of specific AKT phosphatases. Mechanistically, METTL14-mediated m6A installation promotes decay of transcripts encoding prostaglandin synthases and their regulators in human and mouse brown adipocytes in a YTHDF2/3-dependent manner. Collectively, these findings reveal a novel biological mechanism in the m6A-dependent regulation of the BAT secretome in modulating systemic insulin sensitivity in both mice and humans. Presentation: 6/1/2024

Cold Exposure Alleviates T2DM Through Plasma-Derived Extracellular Vesicles.

Anecdotal reports have praised the benefits of cold exposure, exemplified by activities like winter swimming and cold water immersion. Cold exposure has garnered acclaim for its potential to confer benefits and potentially alleviate diabetes. We posited that systemic cold temperature (CT, 4-8°C) likely influences the organism's blood components through ambient temperature, prompting our investigation into the effects of chronic cold exposure on type 2 diabetic (T2DM) mice and our initial exploration of how cold exposure mitigates the incidence of T2DM. The effects of CT (4-8°C) or room temperature (RT, 22-25°C) on T2DM mice were investigated. Mice blood and organ specimens were collected for fully automated biochemical testing, ELISA, HE staining, immunohistochemistry, and immunofluorescence. Glucose uptake was assessed using flow cytometry with 2-NBDG. Changes in potential signaling pathways such as protein kinase B (AKT), phosphorylated AKT (p-AKT), insulin receptor substrates 1 (IRS1), and phosphorylated IRS1 (p-IRS1) were evaluated by Western blot. CT or CT mice plasma-derived extracellular vesicles (CT-EVs) remarkably reduced blood glucose levels and improved insulin sensitivity in T2DM mice. This treatment enhanced glucose metabolism, systemic insulin sensitivity, and insulin secretion function while promoting glycogen accumulation in the liver and muscle. Additionally, CT-EVs treatment protected against the streptozocin (STZ)-induced destruction of islets in T2DM mice by inhibiting β-cell apoptosis. CT-EVs also shielded islets from destruction and increased the expression of p-IRS1 and p-AKT in adipocytes and hepatocytes. In vitro experiments further confirmed its pro-insulin sensitivity effect. Our data indicate that cold exposure may have a potentially beneficial effect on the development of T2DM, mainly through the anti-diabetic effect of plasma-derived EVs released during cold stimulation. This phenomenon could significantly contribute to understanding the lower prevalence of diabetes in colder regions.

Chromium and Palmitic Acid Supplementation Modulate Adipose Tissue Insulin Sensitivity in Postpartum Dairy Cows

Periparturient dairy cows exhibit intense lipolysis driven by reduced dry matter intake, enhanced energy needs, and the loss of adipose tissue (AT) insulin sensitivity. Extended periods of low insulin sensitivity and negative energy balance induce lipolysis dysregulation, leading to increased disease susceptibility and poor lactation performance. Chromium (Cr) supplementation improves systemic insulin sensitivity, while palmitic acid (PA) increases energy availability for milk production. However, the effect of supplementing Cr and PA alone or in combination on insulin sensitivity in AT is unknown. Thirty-two multiparous cows were used in a randomized complete block design experiment and randomly assigned to one of 4 diets fed from 1 to 24 DIM. Diets included: control, no supplementation (CON, n = 8); Cr (Cr-propionate at 0.45 ppm Cr/kg DM, n = 8); PA (1.5% DM, n = 8); or Cr+PA (n = 8). Plasma samples were collected at -13 ± 5.1 d prepartum (PreP), and 14.4 ± 1.9d (PP1) and 21 ± 1.9d (PP2) after calving for albumin, BHB, BUN, calcium, cholesterol, glucose, nonesterified fatty acids (NEFA), total protein, iron, transferrin, triglycerides, and oxylipids quantification. Subcutaneous AT (SCAT) explants were collected at PreP, PP1 and PP2 and incubated in the presence of the lipolytic agent isoproterenol (ISO = 1 µM, BASAL = 0 µM) for 3 h. The antilipolytic effect of insulin (1µL/L) on SCAT explants was evaluated during ISO stimulation (IN+ISO). Lipolysis was quantified by glycerol release in the media (nmol glycerol/mg AT). Macrophage infiltration and adipocyte size were measured using hematoxylin and eosin-stained AT sections and immunohistochemistry. Cr tended to reduce postpartum NEFA concentrations when compared with CON, PA, and Cr+PA. Likewise, Cr increased the percentage of large adipocytes (>9000 µm2) postpartum compared with other diets. In line with higher lipid content, Cr-fed cows had higher ex-vivo BASAL lipolysis at PP2 when compared with PA and Cr+PA. ISO induced higher lipolysis at PP1 and PP2 but it was not affected by Cr and PA. IN+ISO reduced lipolysis by 29.91 ± 11% in Cr compared with ISO. In contrast, IN+ISO did not affect ISO lipolysis in CON, PA, and Cr+PA. Plasma transferrin was reduced by Cr. At PP2, PA cows had 3.3-fold higher macrophage infiltration in SCAT when compared with CON and Cr. Plasma 9-HODE and 9-oxoODE were increased by Cr+PA. PA increased plasma 13-oxoODE and Cr increased the ratio of 13-HODE:13-oxoODE. PA increased 5-iso Prostaglandin F2α-VI. Our results demonstrate that supplementing Cr during the immediate postpartum enhances SCAT insulin sensitivity and lipid accumulation. Further studies should determine the effects and mechanisms of action of Cr and PA on AT lipogenesis, adipogenesis, and their impact on lactation performance.

Fiery Connections: Macrophage-Mediated Inflammation, the Journey from Obesity to Type 2 Diabetes Mellitus and Diabetic Kidney Disease.

The high prevalence of diabetes mellitus (DM) poses a significant public health challenge, with diabetic kidney disease (DKD) as one of its most serious consequences. It has become increasingly clear that type 2 DM (T2D) and the complications of DKD are not purely metabolic disorders. This review outlines emerging evidence related to the step-by-step contribution of macrophages to the development and progression of DKD in individuals who specifically develop T2D as a result of obesity. The macrophage is a prominent inflammatory cell that contributes to obesity, where adipocyte hypertrophy leads to macrophage recruitment and eventually to the expansion of adipose tissue. The recruited macrophages secrete proinflammatory cytokines, which cause systemic inflammation, glucose dysregulation, and insulin sensitivity, ultimately contributing to the development of T2D. Under such pathological changes, the kidney is susceptible to elevated glucose and thereby activates signaling pathways that ultimately drive monocyte recruitment. In particular, the early recruitment of proinflammatory macrophages in the diabetic kidney produces inflammatory cytokines/chemokines that contribute to inflammation and tissue damage associated with DKD pathology. Macrophage activation and recruitment are crucial inciting factors that also persist as DKD progresses. Thus, targeting macrophage activation and function could be a promising therapeutic approach, potentially offering significant benefits for managing DKD at all stages of progression.

Adipose tissue insulin resistance in young Japanese women is associated with metabolic abnormalities and dehydroepiandrosterone-sulfate.

The proportion of young Japanese women who are underweight is exceptionally high. We previously showed that the prevalence of impaired glucose tolerance (IGT) was high in underweight young Japanese women, and that IGT was characterized by high free fatty acid levels and adipose tissue insulin resistance (ATIR). As the next step, this study aimed to explore factors associated with elevated ATIR in this population. Ninety-eight young, healthy, underweight women participated in this study. To investigate the relationship between ATIR and metabolic parameters, participants were divided into three groups (Low, Medium, and High) according to ATIR level. Body composition examination, oral glucose tolerance testing, and blood biochemical analysis were performed; Adipo-IR and the Matsuda index were used as indices of ATIR and systemic insulin sensitivity, respectively. Participants in the High ATIR group had the highest prevalence of IGT (25%), and significantly higher body fat percentage, whole-body insulin resistance, and levels of insulin-like growth factor-1 and dehydroepiandrosterone sulfate (DHEA-S) than the other two groups. They were also significantly younger and had higher systolic blood pressure than the Low ATIR group. Multiple regression analysis showed that DHEA-S, which is known to enhance lipolysis in adipose tissue, was an independent correlate of ATIR. Underweight Japanese women with high ATIR had impaired metabolism, a higher prevalence of IGT, higher systemic insulin resistance, and higher systolic blood pressure. DHEA-S was a determinant of high ATIR levels.

Long-term swimming exercise attenuates right ventricular hypertrophy via modulating meta-inflammation in monocrotaline-induced pulmonary hypertensive rats

Pulmonary arterial hypertension (PAH) is a complex disease characterized by elevated pulmonary vascular resistance, resulting in right ventricular (RV) hypertrophy and, eventually, failure, which remains the primary cause of mortality in PAH patients. While current PAH therapies primarily target vascular abnormalities, most fail to address RV dysfunction. Therefore, improving RV function is a critical treatment goal. Exercise has emerged as an effective intervention for PAH, but the specific impact of swimming exercise on this disease and its associated pathological changes has been less extensively studied. In this study, we investigated the effects of swimming training (60 min/day, 5 days/week for 4 weeks) on monocrotaline (MCT; 60 mg/kg, i. p.)-induced PAH in rats. Our findings demonstrate that swimming significantly attenuates RV hypertrophy and reduces mean pulmonary arterial pressure (MPAP), mitigating the detrimental effects of PAH. Furthermore, we observed structural remodeling in the right ventricle, including increased myocardial necrosis, collagen deposition, and fibrosis-related protein expression. Swimming exercise training was found to reduce these pathological changes, suggesting a protective effect on the right ventricle. Mechanistically, our study revealed the crucial role of meta-inflammation in PAH and the anti-PAH effects of exercise. Swimming training attenuated macrophage accumulation, reduced serum inflammatory cytokines, and improved systemic and RV insulin sensitivity, highlighting its potential to modulate meta-inflammatory processes. In summary, our study suggests that swimming training exerts a beneficial effect on RV function and hypertrophy in MCT-induced PAH rats by targeting meta-inflammation. These results underscore the potential value of exercise-based rehabilitation as a complementary therapy for PAH patients.

M6A mRNA methylation in brown fat regulates systemic insulin sensitivity via an inter-organ prostaglandin signaling axis independent of UCP1

Brown adipose tissue (BAT) regulates systemic metabolism by releasing signaling lipids. N6-methyladenosine (m6A) is the most prevalent and abundant post-transcriptional mRNA modification and has been reported to regulate BAT adipogenesis and energy expenditure. Here, we demonstrate that the absence of m6A methyltransferase-like 14 (METTL14) modifies the BAT secretome to improve systemic insulin sensitivity independent of UCP1. Using lipidomics, we identify prostaglandin E2 (PGE2) and prostaglandin F2a (PGF2a) as BAT-secreted insulin sensitizers. PGE2 and PGF2a inversely correlate with insulin sensitivity in humans and protect mice from high-fat-diet-induced insulin resistance by suppressing specific AKT phosphatases. Mechanistically, METTL14-mediated m6A promotes the decay of PTGES2 and CBR1, the genes encoding PGE2 and PGF2a biosynthesis enzymes, in brown adipocytes via YTHDF2/3. Consistently, BAT-specific knockdown of Ptges2 or Cbr1 reverses the insulin-sensitizing effects in M14KO mice. Overall, these findings reveal a novel biological mechanism through which m6A-dependent regulation of the BAT secretome regulates systemic insulin sensitivity.

Pulmo-protection of long-term swimming exercise via improving insulin sensitivity in monocrotaline-induced pulmonary hypertensive rats

Exercise has been recognized as an effective intervention in the treatment of pulmonary arterial hypertension (PAH), supported by numerous studies. However, the precise effects of exercise on pulmonary function remain to be fully elucidated. In this study, using a rat model of swimming exercise training and monocrotaline-induced PAH, we aimed to explore its impact on pulmonary morphology and function. Our investigations revealed that MCT-treated rats exhibited augmented mean pulmonary arterial pressure (MPAP) and pulmonary vascular remodeling, which can be attenuated by 4 weeks of swimming exercise training (60 min/day, 5 days/week). Notably, MCT-treated rats showed impaired pulmonary function, as manifested by decreased tidal volume and dynamic compliance, which were reversed by exercise training. Assessment of pulmonary substrate in PAH rats indicated a prominent pro-inflammatory substrate, evidenced by macrophage accumulation through quantitative immunohistological analysis of macrophage-like cell expression (CD68), and extracellular matrix remodeling, evaluated by Masson staining. Importantly, both the pro-inflammatory substrate and extracellular matrix remodeling were ameliorated by swimming exercise training. Additionally, serum biochemical analysis demonstrated elevated levels of low-density lipoprotein cholesterol and Apolipoprotein B following MCT treatment, which were reduced with exercise intervention. Moreover, exercise enhanced systemic insulin sensitivity in both MCT-treated and untreated rats. Notably, MCT and exercise treatment both decreased fasting blood glucose (FBG) levels in rats, whereas exercise training reinstated FBG levels to normal in MCT-treated rats. In summary, our study suggests that swimming exercise confers a pulmonary protective effect in MCT-induced PAH rats, highlighting the potential importance of exercise-based rehabilitation in the management of PAH.

Abstract 3025: Association Of Systemic Insulin Sensitivity With Walking Distance In Peripheral Artery Disease

Background: Skeletal muscle in patients with peripheral artery disease (PAD) is subjected to chronic ischemia and is known to be insulin resistant. The association of insulin resistance with walking distance in unclear. Research Question: Does systemic insulin sensitivity (assessed by Homeostatic Model Assessment of Insulin Resistance [HOMA-IR] and Adipose tissue insulin resistance index [Adipo-IR]) associate with 6-minute walk test distance (6MWT)? Aims: To understand the role insulin resistance plays in ambulatory impairment in PAD. Methods: Patients with PAD (defined as ABI <0.85) and age-matched controls (ABI 1.00-1.40) were recruited and underwent measurements of fasting glucose, free fatty acids (FFA), and insulin followed by 6-minute walk testing. HOMA-IR was calculated as (glucose [mg/dL] x insulin [uU/mL])/405 and Adipo-IR was calculated as FFA (mmol/L) x insulin (uU/mL). Comparisons between controls and those with PAD were done with Mann-Whitney U tests. Linear regression modeling was used to assess the association of insulin sensitivity with 6MWT. Results: Seventy subjects (median [IQR] age 67.5 [61.0, 73.0] years, 45 (64.3%) males) were recruited, including 20 controls and 50 with PAD. Insulin levels were significantly high in those with PAD (9.6 vs 12.1 uU/mL, p=0.05) while FFA (0.37 vs 0.34 mmol/L, p=0.04) levels were lower. Glucose levels were similar (77.9 vs 79.5 mg/dL, p=0.53). HOMA-IR was significantly higher in PAD (2.4 vs 2.0, p=0.03) while Adipo-IR was similar (3.9 vs 3.7, p=2.42). Insulin level, HOMA-IR, and Adipo-IR were significantly associated with 6MWT distance in univariate analysis, but no association was seen after adjusting for ABI, which strongly associated with walking distance. Conclusion: Patients with PAD exhibit systemic insulin resistance, although ABI was more strongly associated with 6MWT distance than the degree of insulin sensitivity.

Adipose tissue macrophage–derived microRNA-210-3p disrupts systemic insulin sensitivity by silencing GLUT4 in obesity

Management of chronic obesity-associated metabolic disorders is a key challenge for biomedical researchers. During chronic obesity, visceral adipose tissue (VAT) undergoes substantial transformation characterized by a unique lipid-rich hypoxic AT microenvironment (ATenv) which plays a crucial role in VAT dysfunction, leading to insulin resistance (IR) and type 2 diabetes(T2D). Here, we demonstrate that obese ATenv triggers the release of miR-210-3p microRNA-loaded extracellular vesicles (EVs) from adipose tissue macrophages (ATMs), which disseminate miR-210-3p to neighboring adipocytes, skeletal muscle cells, and hepatocytes through paracrine and endocrine actions, thereby influencing insulin sensitivity. Moreover, EVs collected from Dicer-silenced miR-210-3p-overexpressed bone marrow-derived macrophages (BMDMs), induce glucose intolerance and IR in lean mice. Mechanistically, miR-210-3p interacts with the 3′-UTR of GLUT4 mRNA and silences its expression, compromising cellular glucose uptake and insulin sensitivity. Therapeutic inhibition of miR-210-3p in VAT notably rescues high-fat diet (HFD)-fed mice from obesity-induced systemic glucose intolerance. Thus, targeting ATM-specific miR-210-3p during obesity could be a promising strategy for managing IR and T2D.

TM4SF19-mediated control of lysosomal activity in macrophages contributes to obesity-induced inflammation and metabolic dysfunction

Adipose tissue (AT) adapts to overnutrition in a complex process, wherein specialized immune cells remove and replace dysfunctional and stressed adipocytes with new fat cells. Among immune cells recruited to AT, lipid-associated macrophages (LAMs) have emerged as key players in obesity and in diseases involving lipid stress and inflammation. Here, we show that LAMs selectively express transmembrane 4 L six family member 19 (TM4SF19), a lysosomal protein that represses acidification through its interaction with Vacuolar-ATPase. Inactivation of TM4SF19 elevates lysosomal acidification and accelerates the clearance of dying/dead adipocytes in vitro and in vivo. TM4SF19 deletion reduces the LAM accumulation and increases the proportion of restorative macrophages in AT of male mice fed a high-fat diet. Importantly, male mice lacking TM4SF19 adapt to high-fat feeding through adipocyte hyperplasia, rather than hypertrophy. This adaptation significantly improves local and systemic insulin sensitivity, and energy expenditure, offering a potential avenue to combat obesity-related metabolic dysfunction.

Reciprocal activity of AgRP and POMC neurons governs coordinated control of feeding and metabolism

Agouti-related peptide (AgRP)-expressing and proopiomelanocortin (POMC)-expressing neurons reciprocally regulate food intake. Here, we combine non-interacting recombinases to simultaneously express functionally opposing chemogenetic receptors in AgRP and POMC neurons for comparing metabolic responses in male and female mice with simultaneous activation of AgRP and inhibition of POMC neurons with isolated activation of AgRP neurons or isolated inhibition of POMC neurons. We show that food intake is regulated by the additive effect of AgRP neuron activation and POMC neuron inhibition, while systemic insulin sensitivity and gluconeogenesis are differentially modulated by isolated-versus-simultaneous regulation of AgRP and POMC neurons. We identify a neurocircuit engaging Npy1R-expressing neurons in the paraventricular nucleus of the hypothalamus, where activated AgRP neurons and inhibited POMC neurons cooperate to promote food consumption and activate Th+ neurons in the nucleus tractus solitarii. Collectively, these results unveil how food intake is precisely regulated by the simultaneous bidirectional interplay between AgRP and POMC neurocircuits.

Adipocyte p53 coordinates the response to intermittent fasting by regulating adipose tissue immune cell landscape

In obesity, sustained adipose tissue (AT) inflammation constitutes a cellular memory that limits the effectiveness of weight loss interventions. Yet, the impact of fasting regimens on the regulation of AT immune infiltration is still elusive. Here we show that intermittent fasting (IF) exacerbates the lipid-associated macrophage (LAM) inflammatory phenotype of visceral AT in obese mice. Importantly, this increase in LAM abundance is strongly p53 dependent and partly mediated by p53-driven adipocyte apoptosis. Adipocyte-specific deletion of p53 prevents LAM accumulation during IF, increases the catabolic state of adipocytes, and enhances systemic metabolic flexibility and insulin sensitivity. Finally, in cohorts of obese/diabetic patients, we describe a p53 polymorphism that links to efficacy of a fasting-mimicking diet and that the expression of p53 and TREM2 in AT negatively correlates with maintaining weight loss after bariatric surgery. Overall, our results demonstrate that p53 signalling in adipocytes dictates LAM accumulation in AT under IF and modulates fasting effectiveness in mice and humans.

Crocus sativus tepals extract suppresses subcutaneous adipose tissue hypertrophy and improves systemic insulin sensitivity in mice on high-fat diet.

Obesity is a pressing problem worldwide for which standard therapeutic strategies have limited effectiveness. The use of natural products seems to be a promising approach to alleviate obesity and its associated complications. The tepals of Crocus sativus (Cr) plant, usually wasted in saffron production, are an unexplored source of bioactive compounds. Our aim was to elucidate the mechanisms of Cr tepals extract in obesity by investigating its effects on adipocyte differentiation, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) hypertrophy, and lipid metabolism in an animal model of diet-induced obesity. To this end, mouse 3T3-F442A preadipocytes were treated with Cr tepals extract and the expression of adipocyte differentiation genes was determined. Caloric intake, body mass, triglycerides, systemic insulin sensitivity, histology, insulin signaling, and lipid metabolism in VAT and SAT were analyzed in mice fed a 60% fat diet for 14 weeks and treated orally with Cr tepals extract during the last 5 weeks of the diet. We demonstrated for the first time that Cr tepals extract inhibits adipocyte differentiation in vitro. The animal model confirmed that oral treatment with Cr tepals extract results in weight loss, improved systemic insulin sensitivity, lower triglycerides, and improved lipid peroxidation. The suppressive effect of Cr tepals extract on adipocyte hypertrophy and inflammation was observed only in SAT, which, together with preserved SAT insulin signaling, most likely contributed to improved systemic insulin sensitivity. Our results suggest the functionality of SAT as a possible target for the treatment of obesity and its complications.

Ceramide on the road to insulin resistance and immunometabolic disorders in transition dairy cows: driver or passenger?

Dairy cows must undergo profound metabolic and endocrine adaptations during their transition period to meet the nutrient requirements of the developing fetus, parturition, and the onset of lactation. Insulin resistance in extrahepatic tissues is a critical component of homeorhetic adaptations in periparturient dairy cows. However, due to increased energy demands at calving that are not followed by a concomitant increase in dry matter intake, body stores are mobilized, and the risk of metabolic disorders dramatically increases. Sphingolipid ceramides involved in multiple vital biological processes, such as proliferation, differentiation, apoptosis, and inflammation. Three typical pathways generate ceramide, and many factors contribute to its production as part of the cell's stress response. Based on lipidomic profiling, there has generally been an association between increased ceramide content and various disease outcomes in rodents. Emerging evidence shows that ceramides might play crucial roles in the adaptive metabolic alterations accompanying the initiation of lactation in dairy cows. A series of studies also revealed a negative association between circulating ceramides and systemic insulin sensitivity in dairy cows experiencing severe negative energy balance. Whether ceramide acts as a driver or passenger in the metabolic stress of periparturient dairy cows is an unknown but exciting topic. In the present review, we discuss the potential roles of ceramides in various metabolic dysfunctions and the impacts of their perturbations. We also discuss how this novel class of bioactive sphingolipids has drawn interest in extrahepatic tissue insulin resistance and immunometabolic disorders in transition dairy cows. We also discuss the possible use of ceramide as a new biomarker for predicting metabolic diseases in cows and highlight the remaining problems.

The impact of bed rest on human skeletal muscle metabolism

Insulin sensitivity and metabolic flexibility decrease in response to bed rest, but the temporal and causal adaptations in human skeletal muscle metabolism are not fully defined. Here, we use an integrative approach to assess human skeletal muscle metabolism during bed rest and provide a multi-system analysis of how skeletal muscle and the circulatory system adapt to short- and long-term bed rest (German Clinical Trials: DRKS00015677). We uncover that intracellular glycogen accumulation after short-term bed rest accompanies a rapid reduction in systemic insulin sensitivity and less GLUT4 localization at the muscle cell membrane, preventing further intracellular glycogen deposition after long-term bed rest. We provide evidence of a temporal link between the accumulation of intracellular triglycerides, lipotoxic ceramides, and sphingomyelins and an altered skeletal muscle mitochondrial structure and function after long-term bed rest. An intracellular nutrient overload therefore represents a crucial determinant for rapid skeletal muscle insulin insensitivity and mitochondrial alterations after prolonged bed rest.

Reappraisal of Adipose Tissue Inflammation in Obesity.

Chronic low-grade inflammation is a central component in the pathogenesis of obesity-related expansion of adipose tissue and complications in other metabolic tissues. Five different signaling pathways are defined as dominant determinants of adipose tissue inflammation: These are increased circulating endotoxin due to dysregulation in the microbiota-gut-brain axis, systemic oxidative stress, macrophage accumulation, and adipocyte death. Finally, the nucleotide-binding and oligomerization domain (NOD) leucine-rich repeatfamily pyrin domain-containing 3 (NLRP3) inflammasome pathway is noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome and associated metabolic inflammation play an important role in the relationships among fatty acids and obesity. Several highly active molecules, including primarily leptin, resistin, adiponectin, visfatin, and classical cytokines, are abundantly released from adipocytes. The most important cytokines that are released by inflammatory cells infiltrating obese adipose tissue are tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1) (CCL-2), and IL-1. All these molecules mentioned above act on immune cells, causing local and then general inflammation. Three metabolic pathways are noteworthy in the development of adipose tissue inflammation: toll-like receptor 4 (TLR4)/phosphatidylinositol-3'-kinase (PI3K)/Protein kinase B (Akt) signaling pathway, endoplasmic reticulum (ER) stress-derived unfolded protein response (UPR), and inhibitor of nuclear factor kappa-B kinase beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway. In fact, adipose tissue inflammation is an adaptive response that contributes to a visceral depot barrier that effectively filters gut-derived endotoxin. Excessive fatty acid release worsens adipose tissue inflammation and contributes to insulin resistance. However, suppression of adipose inflammation in obesity with anti-inflammatory drugs is not a rational solution and paradoxically promotes insulin resistance, despite beneficial effects on weight gain. Inflammatory pathways in adipocytes are indeed indispensable for maintaining systemic insulin sensitivity. Cannabinoid type 1 receptor (CB1R) is important in obesity-induced pro-inflammatory response; however, blockade of CB1R, contrary to anti-inflammatory drugs, breaks the links between insulin resistance and adipose tissue inflammation. Obesity, however, could be decreased by improving leptin signaling, white adipose tissue browning, gut microbiota interactions, and alleviating inflammation. Furthermore, capsaicin synthesized by chilies is thought to be a new and promising therapeutic option in obesity, as it prevents metabolic endotoxemia and systemic chronic low-grade inflammation caused by high-fat diet.

Apolipoprotein E (ApoE) orchestrates adipose tissue inflammation and metabolic disorders through NLRP3 inflammasome

Obesity is a metabolic disorder characterized by the hypertrophy expansion of adipose tissue, resulting in dysregulated energy metabolism, and accompanied by chronic low-grade inflammation. Adipose tissue macrophages (ATMs), a principal component of inflammation, respond to microenvironment signals and modulate adipose tissue remodeling and metabolic processes situation-specific. However, the mechanisms governing how the organism maintains equilibrium between its chronic inflammation and metabolism still need to be understood. Here, we describe a novel role of apolipoprotein E (ApoE), which associated with lipid particles, in maintaining fat deposition and system metabolic inflammation. Using human samples and mouse models, we show that ApoE is robustly downregulated in obese individuals, db/db mice, and mice of high-fat diet (HFD) feeding and increased in obese subjects with diabetes. Furthermore, we found that ApoE deficiency mice globally prevented obesity by restraining adipose tissue expansion and improved systemic glucose tolerance and insulin sensitivity. However, macrophage contributed to metabolic inflammation due to increased IL-1β production in adipose tissue from ApoE-/- mice induced by HFD. Our results suggest that the role of ApoE in regulating obesity and obesity-associated glucose dysregulation is inconsistent. Mechanistically, ApoE modulates of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome priming and activation step. Thus, our studies might provide new sights into ApoE, which is required for obesity-induced hyperglycemia, hyperinsulinism, and adaptive inflammation responses but diminishes the tolerance towards a subsequent metabolic inflammatory challenge. Our study shed new light on the integral role of apolipoprotein APOE in immunometabolism and adipose tissue homeostasis.

SGLT2 inhibitor improves kidney function and morphology by regulating renal metabolism in mice with diabetic kidney disease

BackgroundDiabetic kidney disease (DKD) is a secondary complication of diabetes mellitus and a leading cause of chronic kidney disease. AimTo investigate the impact of long-term canagliflozin treatment on DKD and elucidate its underlying mechanism. MethodsDKD model was established using high-fat diet and streptozotocin in male C57BL/6J mice (n = 30). Mice were divided into five groups and treated for 12 weeks. 1) normal control mice, 2) DKD model, 3) mice treated low-dose of canagliflozin, 4) high-dose of canagliflozin and 5) β-hydroxybutyrate. Mice kidney morphology and function were evaluated, and a metabolomics analysis was performed. ResultsCanagliflozin treatment reduced blood creatinine and urine nitrogen levels and improved systemic insulin sensitivity and glucose tolerance in diabetic mice. Additionally, a decrease in histological lesions including collagen and lipid deposition in the kidneys was observed. β-hydroxybutyrate treatment did not yield a comparable outcome. The metabolomics analysis revealed that canagliflozin induced alterations in amino acid metabolism profiles in the renal tissue of diabetic mice. ConclusionCanagliflozin protects the kidneys of diabetic mice by increasing the levels of essential amino acids, promoting mitochondrial homeostasis, mitigating oxidative stress, and stimulating the amino acid-dependent tricarboxylic acid cycle.