Aging Reduces Insulin Clearance in Mice

The P300-ARRDC3 axis participates in maternal subclinical hypothyroidism and is involved in abnormal hepatic insulin sensitivity in adult offspring

Numerous studies have suggested potential associations between maternal subclinical hypothyroidism (SCH) and adverse metabolic outcomes in offspring, however, the underlying mechanism remains unclear. In this study, we generated a maternal SCH mouse model by administering 50 ppm 6-propyl-2-thiouracil (PTU) in the drinking water of pregnant mice until delivery. This model was used to investigate the mechanisms influencing glucose metabolism in offspring. RNA sequencing (RNA-seq) revealed a substantial increase in ARRDC3 expression in the livers of the offspring of the SCH model mice, which may contribute to insulin resistance. Additionally, the phosphorylation levels of key proteins in the insulin signalling pathway, such as protein kinase B (Akt), glycogen synthase kinase 3 beta (GSK-3β), and Forkhead box protein O1 (FoxO1), were correspondingly reduced in the SCH offspring. Moreover, overexpression of ARRDC3 in Hepa1‒6 cells suppressed the Akt/GSK-3β/FoxO1 signalling pathway and increased the expression of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), which was consistent with the molecular changes observed in SCH offspring. Our results also indicated that the upregulation of ARRDC3 in SCH offspring may result from increased H3K27 acetylation of the ARRDC3 promoter region, driven by elevated expression of P300. Importantly, adequate L-T4 supplementation during pregnancy improved insulin sensitivity and reversed the molecular alterations in the insulin signalling pathway observed in SCH offspring. In conclusion, exposure to intrauterine SCH resulted in altering the P300-ARRDC3 axis in offspring and impaired insulin sensitivity by disrupting the Akt/GSK-3β/FoxO1 signalling pathway. Timely L-T4 supplementation during pregnancy is an effective strategy to prevent insulin resistance in offspring of SCH mothers. This study elucidates potential molecular mechanisms behind insulin resistance in SCH offspring and suggests novel therapeutic targets for treating metabolic disorders related to maternal SCH.

Reduced insulin clearance in paediatric metabolic (dysfunction)-associated fatty liver disease and its dual role in beta-cell offload and diabetes risk

AIM

Diminished hepatic insulin clearance (HIC) is observed in obese adults and is presumed to be mediated by fatty liver. However, few reports have examined HIC in Chinese children with metabolic (dysfunction)-associated fatty liver disease (MAFLD). This study aimed to investigate the correlation between HIC, insulin sensitivity and β-cell function in obese Chinese children with MAFLD.

METHODS

In total, 204 obese children (74 MAFLD) aged 4-17 years were enrolled into this study. HIC, insulin sensitivity and β-cell function were calculated using the oral glucose tolerance test (1.75 g/kg body weight). Correlation analyses between the HIC and clinical variables were performed using Pearson's product-moment correlation coefficients. HIC and glucose homeostasis were assessed in a high-fat diet mouse model, and liver samples were collected for molecular analysis.

RESULTS

Obese children with MAFLD exhibited significantly lower HIC (AUCC-peptide/insulin ratio, p = 0.0019), higher insulin resistance (homeostatic model assessment of insulin resistance, p = 0.002), and increased compensatory β-cell function (homeostatic model assessment-β, p = 0.046) than obese children without liver involvement. Notably, HIC was negatively correlated with insulin sensitivity (r = -0.5035, p < 0.0001) and β-cell function (r = -0.4576, p < 0.0001). However, pancreatic β-cell dysfunction (p = 0.046) was accompanied by future reduced HIC (p = 0.034) in children with MAFLD in prediabetes. In a high-fat diet mouse model, MAFLD mice showed a 50% reduction in insulin-degrading enzyme expression, consistent with the observed decrease in HIC.

CONCLUSIONS

A lower HIC may offload pancreatic β-cells at an early stage. However, obese children with MAFLD are at risk of developing diabetes, and preventive efforts should be prioritized.

The onset and the development of cardiometabolic aging: an insight into the underlying mechanisms

Metabolic compromise is crucial in aggravating age-associated chronic inflammation, oxidative stress, mitochondrial damage, increased LDL and triglycerides, and elevated blood pressure. Excessive adiposity, hyperglycemia, and insulin resistance due to aging are associated with elevated levels of damaging free radicals, inducing a proinflammatory state and hampering immune cell activity, leading to a malfunctioning cardiometabolic condition. The age-associated oxidative load and redox imbalance are contributing factors for cardiometabolic morbidities via vascular remodelling and endothelial damage. Recent evidence has claimed the importance of gut microbiota in maintaining regular metabolic activity, which declines with chronological aging and cardiometabolic comorbidities. Genetic mutations, polymorphic changes, and environmental factors strongly correlate with increased vulnerability to aberrant cardiometabolic changes by affecting key physiological pathways. Numerous studies have reported a robust link between biological aging and cardiometabolic dysfunction. This review outlines the scientific evidence exploring potential mechanisms behind the onset and development of cardiovascular and metabolic issues, particularly exacerbated with aging.

The Oldest of Old Male C57B/6J Mice Are Protected from Sarcopenic Obesity: The Possible Role of Skeletal Muscle Protein Kinase B Expression

The impact of aging on body composition and glucose metabolism is not well established in C57BL/6J mice, despite being a common pre-clinical model for aging and metabolic research. The purpose of this study was to examine the effect of advancing age on body composition, in vivo glucose metabolism, and skeletal muscle AKT expression in young (Y: 4 months old, n = 7), old (O: 17-18 months old, n = 10), and very old (VO: 26-27 month old, n = 9) male C57BL/6J mice. Body composition analysis, assessed by nuclear magnetic resonance, demonstrated O mice had a significantly greater fat mass and body fat percentage when compared to Y and VO mice. Furthermore, VO mice had a significantly greater lean body mass than both O and Y mice. We also found that the VO mice had greater AKT protein levels in skeletal muscle compared to O mice, an observation that explains a portion of the increased lean body mass in VO mice. During glucose tolerance (GT) testing, blood glucose values were significantly lower in the VO mice when compared to the Y and O mice. No age-related differences were observed in insulin tolerance (IT). We also assessed the glucose response to AMPK activation by 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR). The change in blood glucose following AICAR administration was significantly reduced in VO mice compared to Y and AG mice. Our findings indicate that lean body mass and AKT2 protein expression in muscle are significantly increased in VO mice compared to O mice. The increase in AKT2 likely plays a role in the greater lean body mass observed in the oldest of old mice. Finally, despite the increased GT, VO mice appear to be resistant to AMPK-mediated glucose uptake.

The Influence of BMP6 on Serotonin and Glucose Metabolism

Previous studies have suggested a potential role of bone morphogenetic protein 6 (BMP6) in glucose metabolism, which also seems to be regulated by serotonin (5-hydroxytryptamine, 5HT), a biogenic amine with multiple roles in the organism. In this study, we explored possible interactions between BMP6, serotonin, and glucose metabolism regulation. The effect of BMP6 or 5HT on pancreatic β-cells has been studied in vitro using the INS-1 832/13 rat insulinoma cell line. Studies in vivo have been performed on mice with the global deletion of the Bmp6 gene (BMP6-/-) and included glucose and insulin tolerance tests, gene expression studies using RT-PCR, immunohistochemistry, and ELISA analyses. We have shown that BMP6 and 5HT treatments have the opposite effect on insulin secretion from INS-1 cells. The effect of BMP6 on the 5HT system in vivo depends on the tissue studied, with no observable systemic effect on peripheral 5HT metabolism. BMP6 deficiency does not cause diabetic changes, although a mild difference in insulin tolerance test between BMP6-/- and WT mice was observed. In conclusion, BMP6 does not directly influence glucose metabolism, but there is a possibility that its deletion causes slowly developing changes in glucose and serotonin metabolism, which would become more expressed with ageing.

Bone Marrow Mesenchymal Stem Cell-Derived Nanovesicles Containing H8 Improve Hepatic Glucose and Lipid Metabolism and Exert Ameliorative Effects in Type 2 Diabetes

Purpose

Nanovesicles (NVs) derived from bone mesenchymal stem cells (BMSCs) as drug delivery systems are considered an effective therapeutic strategy for diabetes. However, its mechanism of action remains unclear. Here, we evaluated the efficacy and molecular mechanism of BMSC-derived NVs carrying the curcumin analog H8 (H8-BMSCs-NVs) on hepatic glucose and lipid metabolism in type 2 diabetes (T2D).

Subjects and Methods

Mouse BMSCs were isolated by collagenase digestion and H8-BMSCs-NVs were prepared by microvesicle extrusion. The effects of H8-BMSCs-NVs on hepatic glucose and lipid metabolism were observed in a T2D mouse model and a HepG2 cell insulin resistance model. To evaluate changes in potential signaling pathways, the PI3K/AKT/AMPK signaling pathway and expression levels of G6P and PEPCK were assessed by Western blotting.

Results

H8-BMSCs-NVs effectively improved lipid accumulation in liver tissues and restored liver dysfunction in T2D mice. Meanwhile, H8-BMSCs-NVs effectively inhibited intracellular lipid accumulation in the insulin resistance models of HepG2 cells. Mechanistic studies showed that H8-BMSCs-NVs activated the PI3K/AKT/AMPK signaling pathway and decreased the expression levels of G6P and PEPCK.

Conclusion

These findings demonstrate that H8-BMSCs-NVs improved hepatic glucose and lipid metabolism in T2D mice by activating the PI3K/AKT/AMPK signaling pathway, which provides novel evidence suggesting the potential of H8-BMSCs-NVs in the clinically treatment of T2D patients.

Microglial SCAP deficiency protects against diabetes-associated cognitive impairment through inhibiting NLRP3 inflammasome-mediated neuroinflammation

Hyperglycemia-induced pathological microglial responses and subsequent neuronal damage are notable characteristics of diabetes-associated cognitive impairment (DACI). Cholesterol accumulation in the brain is a prevalent consequence of diabetes mellitus (DM), exacerbating pathological microglial responses. Regarding disordered glucose and lipid metabolism, the Sterol Regulatory Element-Binding Protein (SREBP) cleavage-activating protein (SCAP), a cholesterol sensor, exhibits increased expression and abnormal translocation from the endoplasmic reticulum to the Golgi, amplifying the inflammatory response. Therefore, we hypothesized that overexpression of microglia-SCAP and cholesterol accumulation in DM mice could induce pathological microglial responses associated with DACI. Our type 2 DM mice model presented an abnormal increase in microglial SCAP expression. The functional loss of microglia-specific SCAP in DM mice improved cognitive impairment, neuronal synaptic plasticity deficits, and abnormal microglial responses. Mechanistically, the accumulated SCAP directly bound to and enhanced the activation of the microglial-specific inflammatory amplifier, NLRP3 inflammasome, in Golgi, thereby increasing pathological microglial responses and promoting neuronal damage. These findings indicate an important regulatory axis of microglial responses from SCAP to the NLRP3 inflammasome pathway in microglia. These underscore the crosstalk between cholesterol disorders and pathological microglial responses, offering a promising avenue for pharmaceutical interventions in DACI.

Saturated fatty acid concentrations are predictive of insulin sensitivity and beta cell compensation in dogs

Chronic feeding of a high fat diet (HFD) in preclinical species induces broad metabolic dysfunction characterized by body weight gain, hyperinsulinemia, dyslipidemia and impaired insulin sensitivity. The plasma lipidome is not well characterized in dogs with HFD-induced metabolic dysfunction. We therefore aimed to describe the alterations that occur in the plasma lipid composition of dogs that are fed a HFD and examine the association of these changes with the clinical signs of metabolic dysfunction. Dogs were fed a normal diet (ND) or HFD for 12 weeks. Insulin sensitivity (SI) and beta cell compensation (AIRG) were assessed through an intravenous glucose tolerance test (IVGTT) and serum biochemistry was analyzed before the introduction of HFD and again after 12 weeks of continued ND or HFD feeding. Plasma lipidomics were conducted prior to the introduction of HFD and again at week 8 in both ND and HFD-fed dogs. 12 weeks of HFD feeding resulted in impaired insulin sensitivity and increased beta cell compensation measured by SI (ND mean: 11.5 [mU/l]-1 min-1, HFD mean: 4.7 [mU/l]-1 min-1) and AIRG (ND mean: 167.0 [mU/l]min, HFD mean: 260.2 [mU/l]min), respectively, compared to dogs fed ND over the same duration. Chronic HFD feeding increased concentrations of plasma lipid species and deleterious fatty acids compared to dogs fed a ND. Saturated fatty acid (SFA) concentrations were significantly associated with fasting insulin (R2 = 0.29), SI (R2 = 0.49) and AIRG (R2 = 0.37) in all dogs after 12 weeks, irrespective of diet. Our results demonstrate that chronic HFD feeding leads to significant changes in plasma lipid composition and fatty acid concentrations associated with metabolic dysfunction. High SFA concentrations may be predictive of deteriorated insulin sensitivity in dogs.

Gut microbiota dysbiosis and decreased levels of acetic and propionic acid participate in glucocorticoid-induced glycolipid metabolism disorder

Long-term/high-dose glucocorticoid (GC) use results in glycolipid metabolism disorder, which severely limits its clinical application. The role of the gut microbiota and its metabolites in GC-induced glycolipid metabolism disorder remains unclear. Our previous human study found that obvious gut microbiota dysbiosis characterized by an increasing abundance of Proteobacteria and a decreased abundance of Lachnospiraceae and Faecalibacterium were observed in patients with endogenous hypercortisolism. In this study, we established a mouse model of GC-induced glycolipid metabolism disorder (Dex group) and found that the relative abundances of Proteobacteria and Parasuttrerella were increased, while the abundances of Lachnospiraceae, Faecalibacterium, and Lachnospiraceae_NK4A136_group were decreased significantly in the Dex group. Compared with the control group, serum total short-chain fatty acids (SCFAs), acetic acid, propionic acid, and GLP-1 levels were all decreased in the Dex group. The mRNA expression of the GPR41 receptor and Pcsk1 in the colon was significantly decreased in the Dex group. Furthermore, GC-induced glycolipid metabolism disorder could be alleviated by depletion of the gut microbiota or fecal bacteria transplantation with control bacteria. The abundances of Lachnospiraceae_NK4A136_group and the serum GLP-1 levels were significantly increased, while the abundances of Proteobacteria and Parasutterella were significantly decreased after fecal bacteria transplantation with control bacteria. Our work indicates that gut microbiota dysbiosis and decreased levels of serum acetic acid and propionic acid may participate in GC-induced glycolipid metabolism disorder. These findings may provide novel insights into the prevention and treatment of GC-induced metabolic disorders.IMPORTANCEThe role of the gut microbiota in glucocorticoid (GC)-induced glycolipid metabolism disorder remains unclear. In our study, gut microbiota dysbiosis characterized by an increased abundance of Proteobacteria/Parasuttrerella and a decreased abundance of Lachnospiraceae_NK4A136_group was observed in mice with GC-induced glycolipid metabolism disorder. Some bacteria were shared in our previous study in patients with endogenous hypercortisolism and the mouse model used in the study. Furthermore, the depletion of the gut microbiota and fecal bacteria transplantation with control bacteria could alleviate GC-induced glycolipid metabolism disorder. Plasma acetic acid, propionic acid, and GLP-1 and the mRNA expression of the GPR41 receptor and Pcsk1 in the colon were decreased significantly in mice with GC-induced glycolipid metabolism disorder, which indicated that the gut microbiota/SCFA/GPR41/GLP-1 axis may participate in GC-induced glycolipid metabolism disorder. Our findings indicate that the gut microbiota may serve as a novel therapeutic target for GC-related metabolic disorders.

Long-term physical inactivity induces significant changes in biochemical pathways related to metabolism of proteins and glycerophospholipids in mice

Physical inactivity affects multiple organ systems, including the musculoskeletal system, which upsets the delicate balance of several secretory factors leading to metabolic derailment. This reduces contractile recruitment of the skeletal muscle with dampening of its oxidative capacity resulting in impaired intramuscular lipid metabolism and substrate utilization. We hypothesized that this altered phenotype would also have an indispensable effect on circulatory cytokines and the level of metabolic intermediates. In this study, comparison between sedentary (SED) and exercised (EXER) animal models showed that organismal metabolic parameters (body mass, oxygen utilization and glucose tolerance) are altered based on physical activity. Our data suggest that cytokines linked to glycemic excursions (insulin, c-peptide, glucagon) and their passive regulators (leptin, BDNF, active ghrelin, and GIP) exhibit changes in the SED group. Furthermore, some of the proinflammatory cytokines and myokines were upregulated in SED. Interestingly, serum metabolite analysis showed that the levels of glucogenic amino acids (alanine, glycine, tryptophan, proline and valine), nitrogenous amino acids (ornithine, asparagine, and glutamine) and myogenic metabolites (taurine, creatine) were altered due to the level of physical activity. A pyrimidine nucleoside (uridine), lipid metabolite (glycerol) and ketone bodies (acetoacetate and acetate) were found to be altered in SED. A Spearman rank correlation study between SED and CTRL showed that cytokines build a deformed network with metabolites in SED, indicating significant modifications in amino acids, phosphatidylinositol phosphate and glycerophospholipid metabolic pathways. Overall, long-term physical inactivity reorganizes the profile of proinflammatory cytokines, glucose sensing hormones, and protein and glycerophospholipid metabolism, which might be the initial factors of metabolic diseases due to SED.

Spatial omics: An innovative frontier in aging research

Disentangling the impact of aging on health and disease has become critical as population aging progresses rapidly. Studying aging at the molecular level is complicated by the diverse aging profiles and dynamics. However, the examination of cellular states within aging tissues in situ is hampered by the lack of high-resolution spatial data. Emerging spatial omics technologies facilitate molecular and spatial analysis of tissues, providing direct access to precise information on various functional regions and serving as a favorable tool for unraveling the heterogeneity of aging. In this review, we summarize the recent advances in spatial omics application in multi-organ aging research, which has enhanced the understanding of aging mechanisms from multiple standpoints. We also discuss the main challenges in spatial omics research to date, the opportunities for further developing the technology, and the potential applications of spatial omics in aging and aging-related diseases.

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

Inhibiting Rev-erbα-mediated ferroptosis alleviates susceptibility to myocardial ischemia-reperfusion injury in type 2 diabetes

The complex progression of type-2 diabetes (T2DM) may result in increased susceptibility to myocardial ischemia-reperfusion (IR) injury. IR injuries in multiple organs involves ferroptosis. Recently, the clock gene Rev-erbα has aroused considerable interest as a novel therapeutic target for metabolic and ischemic heart diseases. Herein, we investigated the roles of Rev-erbα and ferroptosis in myocardial IR injury during T2DM and its potential mechanisms. A T2DM model, myocardial IR and a tissue-specific Rev-erbα-/- mouse in vivo were established, and a high-fat high glucose environment with hypoxia-reoxygenation (HFHG/HR) in H9c2 were also performed. After myocardial IR, glycolipid profiles, creatine kinase-MB, AI, and the expression of Rev-erbα and ferroptosis-related proteins were increased in diabetic rats with impaired cardiac function compared to non-diabetic rats, regardless of the time at which IR was induced. The ferroptosis inhibitor ferrostatin-1 decreased AI in diabetic rats given IR and LPO levels in cells treated with HFHG/HR, as well as the expression of Rev-erbα and ACSL4. The ferroptosis inducer erastin increased AI and LPO levels and ACSL4 expression. Treatment with the circadian regulator nobiletin and genetically targeting Rev-erbα via siRNA or CRISPR/Cas9 technology both protected against severe myocardial injury and decreased Rev-erbα and ACSL4 expression, compared to the respective controls. Taken together, these data suggest that ferroptosis is involved in the susceptibility to myocardial IR injury during T2DM, and that targeting Rev-erbα could alleviate myocardial IR injury by inhibiting ferroptosis.

Supplementing L-Citrulline Can Extend Lifespan in C. elegans and Attenuate the Development of Aging-Related Impairments of Glucose Tolerance and Intestinal Barrier in Mice

L-Citrulline (L-Cit) is discussed to possess a protective effect on intestinal barrier dysfunction but also to diminish aging-associated degenerative processes. Here, the effects of L-Cit on lifespan were assessed in C. elegans, while the effects of L-Cit on aging-associated decline were determined in C57BL/6J mice. For lifespan analysis, C. elegans were treated with ±5 mM L-Cit. Twelve-month-old male C57BL/6J mice (n = 8-10/group) fed a standard chow diet received drinking water ± 2.5 g/kg/d L-Cit or 5 g/kg/d hydrolyzed soy protein (Iso-N-control) for 16 or 32 weeks. Additionally, 4-month-old C57BL/6J mice were treated accordingly for 8 weeks. Markers of senescence, glucose tolerance, intestinal barrier function, and intestinal microbiota composition were analyzed in mice. L-Cit treatment significantly extended the lifespan of C. elegans. The significant increase in markers of senescence and signs of impaired glucose tolerance found in 16- and 20-month-old control mice was attenuated in L-Cit-fed mice, which was associated with protection from intestinal barrier dysfunction and a decrease in NO2- levels in the small intestine, while no marked differences in intestinal microbiota composition were found when comparing age-matched groups. Our results suggest that pharmacological doses of L-Cit may have beneficial effects on lifespan in C. elegans and aging-associated decline in mice.

Protectin DX as a therapeutic strategy against frailty in mice

Frailty in aging is driven by the dysregulation of multiple biological pathways. Protectin DX (PDX) is a docosahexaenoic acid (DHA)-derived molecule that alleviates many chronic inflammatory disorders, but its potential effects on frailty remain unknown. Our goal is to identify age-related impairments in metabolic systems and to evaluate the therapeutic potential of PDX on frailty, physical performance, and health parameters. A set of 22-month-old C57BL/6 male and female mice were assigned to vehicle (Old) or PDX daily gavage treatment for 9 weeks, whereas 6-month-old (Adult) mice received only vehicle. Forelimb and hindlimb strength, endurance, voluntary wheel activity and walking speed determined physical performance and were combined with a frailty index score and body weight loss to determine frailty status. Our data shows that old vehicle-treated mice from both sexes had body weight loss paralleling visceromegaly, and Old females also had impaired insulin clearance as compared to the Adult group. Aging was associated with physical performance decline together with higher odds of frailty development. There was also age-driven mesangial expansion and glomerular hypertrophy as well as bone mineral density loss. All of the in vivo and in vitro impairments observed with aging co-occurred with upregulation of inflammatory pathways and Myc signaling as well as downregulation of genes related to adipogenesis and oxidative phosphorylation in liver. PDX attenuated the age-driven physical performance (strength, exhaustion, walking speed) decline, promoted robustness, prevented bone losses and partially reversed changes in hepatic expression of Myc targets and metabolic genes. In conclusion, our data provides evidence of the beneficial therapeutic effect of PDX against features of frailty in mice. Further studies are warranted to investigate the mechanisms of action and the potential for human translation.

Chronic inflammation and the hallmarks of aging

BACKGROUND

Recently, the hallmarks of aging were updated to include dysbiosis, disabled macroautophagy, and chronic inflammation. In particular, the low-grade chronic inflammation during aging, without overt infection, is defined as "inflammaging," which is associated with increased morbidity and mortality in the aging population. Emerging evidence suggests a bidirectional and cyclical relationship between chronic inflammation and the development of age-related conditions, such as cardiovascular diseases, neurodegeneration, cancer, and frailty. How the crosstalk between chronic inflammation and other hallmarks of aging underlies biological mechanisms of aging and age-related disease is thus of particular interest to the current geroscience research.

SCOPE OF REVIEW

This review integrates the cellular and molecular mechanisms of age-associated chronic inflammation with the other eleven hallmarks of aging. Extra discussion is dedicated to the hallmark of "altered nutrient sensing," given the scope of Molecular Metabolism. The deregulation of hallmark processes during aging disrupts the delicate balance between pro-inflammatory and anti-inflammatory signaling, leading to a persistent inflammatory state. The resultant chronic inflammation, in turn, further aggravates the dysfunction of each hallmark, thereby driving the progression of aging and age-related diseases.

MAIN CONCLUSIONS

The crosstalk between chronic inflammation and other hallmarks of aging results in a vicious cycle that exacerbates the decline in cellular functions and promotes aging. Understanding this complex interplay will provide new insights into the mechanisms of aging and the development of potential anti-aging interventions. Given their interconnectedness and ability to accentuate the primary elements of aging, drivers of chronic inflammation may be an ideal target with high translational potential to address the pathological conditions associated with aging.

Short-term physical exercise controls age-related hyperinsulinemia and improves hepatic metabolism in aged rodents

PURPOSE

Aging is associated with changes in glucose homeostasis related to both decreased insulin secretion and/or impaired insulin action, contributing to the high prevalence of type 2 diabetes (T2D) in the elderly population. Additionally, studies are showing that chronically high levels of circulating insulin can also lead to insulin resistance. In contrast, physical exercise has been a strategy used to improve insulin sensitivity and metabolic health. However, the molecular alterations resulting from the effects of physical exercise in the liver on age-related hyperinsulinemia conditions are not yet fully established. This study aimed to investigate the effects of 7 days of aerobic exercise on hepatic metabolism in aged hyperinsulinemic rats (i.e., Wistar and F344) and in Slc2a4^+/- mice (hyperglycemic and hyperinsulinemic mice).

RESULTS

Both aged models showed alterations in insulin and glucose tolerance, which were associated with essential changes in hepatic fat metabolism (lipogenesis, gluconeogenesis, and inflammation). In contrast, 7 days of physical exercise was efficient in improving whole-body glucose and insulin sensitivity, and hepatic metabolism. The Slc2a4^+/- mice presented significant metabolic impairments (insulin resistance and hepatic fat accumulation) that were improved by short-term exercise training. In this scenario, high circulating insulin may be an important contributor to age-related insulin resistance and hepatic disarrangements in some specific conditions.

CONCLUSION

In conclusion, our data demonstrated that short-term aerobic exercise was able to control mechanisms related to hepatic fat accumulation and insulin sensitivity in aged rodents. These effects could contribute to late-life metabolic health and prevent the development/progression of age-related T2D.

Antimicrobial protein REG3A regulates glucose homeostasis and insulin resistance in obese diabetic mice

Innate immune mediators of pathogen clearance, including the secreted C-type lectins REG3 of the antimicrobial peptide (AMP) family, are known to be involved in the regulation of tissue repair and homeostasis. Their role in metabolic homeostasis remains unknown. Here we show that an increase in human REG3A improves glucose and lipid homeostasis in nutritional and genetic mouse models of obesity and type 2 diabetes. Mice overexpressing REG3A in the liver show improved glucose homeostasis, which is reflected in better insulin sensitivity in normal weight and obese states. Delivery of recombinant REG3A protein to leptin-deficient ob/ob mice or wild-type mice on a high-fat diet also improves glucose homeostasis. This is accompanied by reduced oxidative protein damage, increased AMPK phosphorylation and insulin-stimulated glucose uptake in skeletal muscle tissue. Oxidative damage in differentiated C2C12 myotubes is greatly attenuated by REG3A, as is the increase in gp130-mediated AMPK activation. In contrast, Akt-mediated insulin action, which is impaired by oxidative stress, is not restored by REG3A. These data highlight the importance of REG3A in controlling oxidative protein damage involved in energy and metabolic pathways during obesity and diabetes, and provide additional insight into the dual function of host-immune defense and metabolic regulation for AMP.

Regulation of the immune system by the insulin receptor in health and disease

The signaling pathways downstream of the insulin receptor (InsR) are some of the most evolutionarily conserved pathways that regulate organism longevity and metabolism. InsR signaling is well characterized in metabolic tissues, such as liver, muscle, and fat, actively orchestrating cellular processes, including growth, survival, and nutrient metabolism. However, cells of the immune system also express the InsR and downstream signaling machinery, and there is increasing appreciation for the involvement of InsR signaling in shaping the immune response. Here, we summarize current understanding of InsR signaling pathways in different immune cell subsets and their impact on cellular metabolism, differentiation, and effector versus regulatory function. We also discuss mechanistic links between altered InsR signaling and immune dysfunction in various disease settings and conditions, with a focus on age related conditions, such as type 2 diabetes, cancer and infection vulnerability.

Insulin Clearance in Health and Disease

Insulin action is impaired in type 2 diabetes. The functions of the hormone are an integrated product of insulin secretion from pancreatic β-cells and insulin clearance by receptor-mediated endocytosis and degradation, mostly in liver (hepatocytes) and, to a lower extent, in extrahepatic peripheral tissues. Substantial evidence indicates that genetic or acquired abnormalities of insulin secretion or action predispose to type 2 diabetes. In recent years, along with the discovery of the molecular foundation of receptor-mediated insulin clearance, such as through the membrane glycoprotein CEACAM1, a consensus has begun to emerge that reduction of insulin clearance contributes to the disease process. In this review, we consider the evidence suggesting a pathogenic role for reduced insulin clearance in insulin resistance, obesity, hepatic steatosis, and type 2 diabetes.

Senolytic drugs, dasatinib and quercetin, attenuate adipose tissue inflammation, and ameliorate metabolic function in old age

Aging results in an elevated burden of senescent cells, senescence-associated secretory phenotype (SASP), and tissue infiltration of immune cells contributing to chronic low-grade inflammation and a host of age-related diseases. Recent evidence suggests that the clearance of senescent cells alleviates chronic inflammation and its associated dysfunction and diseases. However, the effect of this intervention on metabolic function in old age remains poorly understood. Here, we demonstrate that dasatinib and quercetin (D&Q) have senolytic effects, reducing age-related increase in senescence-associated β-galactosidase, expression of p16 and p21 gene and P16 protein in perigonadal white adipose tissue (pgWAT; all p ≤ 0.04). This treatment also suppressed age-related increase in the expression of a subset of pro-inflammatory SASP genes (mcp1, tnf-α, il-1α, il-1β, il-6, cxcl2, and cxcl10), crown-like structures, abundance of T cells and macrophages in pgWAT (all p ≤ 0.04). In the liver and skeletal muscle, we did not find a robust effect of D&Q on senescence and inflammatory SASP markers. Although we did not observe an age-related difference in glucose tolerance, D&Q treatment improved fasting blood glucose (p = 0.001) and glucose tolerance (p = 0.007) in old mice that was concomitant with lower hepatic gluconeogenesis. Additionally, D&Q improved insulin-stimulated suppression of plasma NEFAs (p = 0.01), reduced fed and fasted plasma triglycerides (both p ≤ 0.04), and improved systemic lipid tolerance (p = 0.006). Collectively, results from this study suggest that D&Q attenuates adipose tissue inflammation and improves systemic metabolic function in old age. These findings have implications for the development of therapeutic agents to combat metabolic dysfunction and diseases in old age.

The bile acid TUDCA reduces age-related hyperinsulinemia in mice

Aging is associated with glucose metabolism disturbances, such as insulin resistance and hyperinsulinemia, which contribute to the increased prevalence of type 2 diabetes (T2D) and its complications in the elderly population. In this sense, some bile acids have emerged as new therapeutic targets to treat TD2, as well as associated metabolic disorders. The taurine conjugated bile acid, tauroursodeoxycholic acid (TUDCA) improves glucose homeostasis in T2D, obesity, and Alzheimer's disease mice model. However, its effects in aged mice have not been explored yet. Here, we evaluated the actions of TUDCA upon glucose-insulin homeostasis in aged C57BL/6 male mice (18-month-old) treated with 300 mg/kg of TUDCA or its vehicle. TUDCA attenuated hyperinsulinemia and improved glucose homeostasis in aged mice, by enhancing liver insulin-degrading enzyme (IDE) expression and insulin clearance. Furthermore, the improvement in glucose-insulin homeostasis in these mice was accompanied by a reduction in adiposity, associated with adipocyte hypertrophy, and lipids accumulation in the liver. TUDCA-treated aged mice also displayed increased energy expenditure and metabolic flexibility, as well as a better cognitive ability. Taken together, our data highlight TUDCA as an interesting target for the attenuation of age-related hyperinsulinemia and its deleterious effects on metabolism.

Intersection of the Orphan G Protein-Coupled Receptor, GPR19, with the Aging Process

G protein-coupled receptors (GPCRs) represent one of the most functionally diverse classes of transmembrane proteins. GPCRs and their associated signaling systems have been linked to nearly every physiological process. They also constitute nearly 40% of the current pharmacopeia as direct targets of remedial therapies. Hence, their place as a functional nexus in the interface between physiological and pathophysiological processes suggests that GPCRs may play a central role in the generation of nearly all types of human disease. Perhaps one mechanism through which GPCRs can mediate this pivotal function is through the control of the molecular aging process. It is now appreciated that, indeed, many human disorders/diseases are induced by GPCR signaling processes linked to pathological aging. Here we discuss one such novel member of the GPCR family, GPR19, that may represent an important new target for novel remedial strategies for the aging process. The molecular signaling pathways (metabolic control, circadian rhythm regulation and stress responsiveness) associated with this recently characterized receptor suggest an important role in aging-related disease etiology.

Life without Proteinase Activated Receptor 2 (PAR2) Alters Body Composition and Glucose Tolerance in Mice

The potential role of proteinase activated receptor 2 (PAR2) in the development of age-related obesity and insulin resistance is not well-understood. To address the hypothesis that deletion of PAR2 might ameliorate age-related obesity and impaired glucose homeostasis, we assessed body composition and insulin action in 18-month-old male PAR2 knockout (PAR2KO-AG), age-matched (AG) and young C57BL6 (YG, 6-month-old) mice. Body composition was measured by magnetic resonance spectroscopy (MRS) and insulin action was assessed by glucose tolerance (GT), insulin tolerance (IT) and AICAR tolerance (AT) testing. AG mice weighed significantly more than YG mice (p = 0.0001) demonstrating age-related obesity. However, PAR2KO-AG mice weighed significantly more than AG mice (p = 0.042), indicating that PAR2 may prevent a portion of age-related obesity. PAR2KO-AG and AG mice had greater fat mass and body fat percentage than YG mice. Similar to body weight, fat mass was greater in PAR2KO-AG mice compared to AG mice (p = 0.045); however, only a trend for greater body fat percentage in PAR2KO-AG compared to AG mice was observed (p = 0.09). No differences existed in lean body mass among the PAR2KO-AG, AG, and YG mice (p = 0.58). With regard to insulin action, the area under the curve (AUC) for GT was lower in PAR2KO-AG compared to AG mice (p = 0.0003) and YG mice (p = 0.001); however, no differences existed for the AUC for IT or AT. Our findings indicate that age-related obesity is not dependent on PAR2 expression.

Pterostilbene Fails to Rescue Insulin Secretion and Sensitivity in Multiple Murine Models of Diabetes

Diabetes incidence is rising globally at an accelerating rate causing issues at both the individual and societal levels. However, partly inspired by Ayurvedic medicine, a naturally occurring compound called pterostilbene has been demonstrated to protect against diabetes symptoms, though mainly in rats. The purpose of this study was to investigate the putative protective effect of pterostilbene on the two main aspects of diabetes, namely insulin resistance and decreased insulin secretion, in mice. To accomplish this, we employed diet-induced obese as well as streptozotocin-induced diabetic C57BL/6NTac mice for fasting glucose homeostasis assessment, tolerance tests and pancreas perfusions. In addition, we used the polygenic model of diabetes TALLYHO/JngJ to assess for prevention of β-cell burnout. We found that the diet-induced obese C57BL/6NTac mice were insulin resistant, but that pterostilbene had no impact on this or on overall glucose regulation. We further found that the reported protective effect of pterostilbene against streptozotocin-induced diabetes was absent in C57BL/6NTac mice, despite a promising pilot experiment. Lastly, we observed that pterostilbene does not prevent or delay onset of β-cell burnout in TALLYHO/JngJ mice. In conjunction with the literature, our findings suggest variations in the response to pterostilbene between species or between strains of species.

Prolonged Consumption of glucose syrup enhances glucose tolerance in mice

There is debate about the metabolic impact of sugar-sweetened beverages. Here, we tested the hypothesis that ad lib consumption of glucose (Gluc) or high-fructose (HiFruc) syrups improves glucose tolerance in mice. We provided C57BL/6 mice with a control (chow and water) or experimental (chow, water and sugar solution) diet across two consecutive 28-day exposure periods, and monitored changes in body composition, glucose tolerance, cephalic-phase insulin release (CPIR) and insulin sensitivity. The sugar solutions contained 11% concentrations of Gluc or HiFruc syrup; these syrups were derived from either corn starch or cellulose. In Experiment 1, consumption of the Gluc diets reliably enhanced glucose tolerance, while consumption of the HiFruc diets did not. Mice on the Gluc diets exhibited higher CPIR (relative to baseline) by the end of exposure period 1, whereas mice on the control and HiFruc diets did not do so until the end of exposure period 2. Mice on the Gluc diets also exhibited higher insulin sensitivity than control mice at the end of exposure period 2, while mice on the HiFruc diets did not. In Experiment 2, we repeated the previous experiment, but limited testing to the corn-based Gluc and HiFruc syrups. We found, once again, that consumption of the Gluc (but not the HiFruc) diet enhanced glucose tolerance, in part by increasing CPIR and insulin sensitivity. These results show that mice can adapt metabolically to high glucose diets, and that this adaptation process involves upregulating at least two components of the insulin response system.

Strain and Age Dependent Entrainable Range of Circadian Behavior in C57BL/6 and BALB/c Mice

The mammalian circadian system has a plasticity in a certain range, rather than a strict 24-hour cycle, with considerable variations among species, strains, and ages. As the most widely used mouse strains in circadian research, C57BL/6 and BALB/c mice were well known to have different internal periods and responses to various non-24-hour light-dark cycles. However, their entrainable range of circadian behavior was not specifically studied, neither was the effect of aging. Besides, it is not well known if mice with appeared behavioral adaptation are really healthy. In the current study, we exposed C57BL/6 and BALB/c mice at 3 months and 18 months old to a series of short (T cycles < 24 h) and long (T cycles > 24 h) light-dark cycles. Wheel running activities were monitored continuously for calculation of the entrainable range and glucose homeostasis was investigated to reflect their health status. Our results showed that the range in both young and old C57BL/6 mice is between T23 and T26. By contrast, due to the strong adaptability to extreme LD cycles, the entrainable range on a circadian scale in both young and old BALB/c mice cannot be well determined. Despite the adaptation appeared at the behavioral level, glucose homeostasis revealed by glucose tolerance test and insulin tolerance test was impaired in mice upon T cycle treatment. In summary, our study explored the entrainment range in two popular mouse strains and suggested that behavioral adaptation may not well reflect their health status.

Long-Term Hypercaloric Diet Consumption Exacerbates Age-Induced Dysmetabolism and Carotid Body Dysfunction: Beneficial Effects of CSN Denervation

Carotid bodies (CBs) are metabolic sensors whose dysfunction is involved in the genesis of dysmetabolic states. Ageing induces significant alterations in CB function also prompting to metabolic deregulation. On the other hand, metabolic disease can accelerate ageing processes. Taking these into account, we evaluated the effect of long-term hypercaloric diet intake and CSN resection on age-induced dysmetabolism and CB function. Experiments were performed in male Wistar rats subjected to 14 or 44 weeks of high-fat high-sucrose (HFHSu) or normal chow (NC) diet and subjected to either carotid sinus nerve (CSN) resection or a sham procedure. After surgery, the animals were kept on a diet for more than 9 weeks. Metabolic parameters, basal ventilation, and hypoxic and hypercapnic ventilatory responses were evaluated. CB type I and type II cells, HIF-1α and insulin receptor (IR), and GLP-1 receptor (GLP1-R)-positive staining were analyzed by immunofluorescence. Ageing decreased by 61% insulin sensitivity in NC animals, without altering glucose tolerance. Short-term and long-term HFHSu intake decreased insulin sensitivity by 55 and 62% and glucose tolerance by 8 and 29%, respectively. CSN resection restored insulin sensitivity and glucose tolerance. Ageing decreased spontaneous ventilation, but short-term or long-term intake of HFHSu diet and CSN resection did not modify basal ventilatory parameters. HFHSu diet increased hypoxic ventilatory responses in young and adult animals, effects attenuated by CSN resection. Ageing, hypercaloric diet, and CSN resection did not change hypercapnic ventilatory responses. Adult animals showed decreased type I cells and IR and GLP-1R staining without altering the number of type II cells and HIF-1α. HFHSu diet increased the number of type I and II cells and IR in young animals without significantly changing these values in adult animals. CSN resection restored the number of type I cells in HFHSu animals and decreased IR-positive staining in all the groups of animals, without altering type II cells, HIF-1α, or GLP-1R staining. In conclusion, long-term hypercaloric diet consumption exacerbates age-induced dysmetabolism, and both short- and long-term hypercaloric diet intakes promote significant alterations in CB function. CSN resection ameliorates these effects. We suggest that modulation of CB activity is beneficial in exacerbated stages of dysmetabolism.

Paternal High-Fat Diet Altered Sperm 5'tsRNA-Gly-GCC Is Associated With Enhanced Gluconeogenesis in the Offspring

Background: Paternal lifestyle, stress and environmental exposures play a crucial role in the health of offspring and are associated with non-genetic inheritance of acquired traits, however the underlying mechanisms are unclear. In this study, we aimed to find out how the sperm tsRNA involved in paternal high-fat diet induced abnormal gluconeogenesis of F1 offspring, and explore the underlying molecular mechanism of its regulation.

Method: We generated a paternal high fat diet (42% kcal fat) model to investigate the mechanism by which paternal diet affects offspring metabolism. Four-week-old C57BL/6J male mice were randomly assigned into two groups to receive either a control diet (CD; 10% kcal fat) or a high-fat (HFD; 42% kcal fat) diet for 10 weeks, and mice from each group were then mated with 8-week-old females with control diet in a 1:2 ratio to generate F1. F0 sperms were isolated and small RNAs was sequenced by high-throughput sequencing. Metabolic phenotypes were examined with both F0 and F1.

Results: A significant increase in body weight was observed with HFD-F0 mice at 8 weeks of age as compared to CD mice at the same age. F0 mice showed impaired glucose tolerance (GTT), resistance to insulin tolerance (ITT) and increased pyruvate tolerance (PTT) at 14 weeks. HFD-F1 male mice showed no significant difference in body weight. An increase in PTT was found at 13 weeks of age and no significant changes in GTT and ITT. PEPCK and G6Pase that related to gluconeogenesis increased significantly in the liver of HFD-F1 male mice. Sperm sequencing results showed that 5′tsRNA-Gly-GCC derived from tRNA-Gly-GCC-2 specifically was remarkably upregulated in sperm of HFD F0 mice. Q-PCR further showed that this tsRNA was also increased in the liver of HFD-F1 comparison with CD-F1 mice. In addition, we found that 5′tsRNA-Gly-GCC can regulate Sirt6-FoxO1 pathway and be involved in the gluconeogenesis pathway in liver.

Conclusion: 5′tsRNA-Gly-GCC that increased in HFD mice mature sperms can promote gluconeogenesis in liver by regulating Sirt6-FoxO1 pathway, which might represent a potential paternal epigenetic factor mediating the intergenerational inheritance of diet-induced metabolic alteration.