Skeletal muscle mitoribosomal defects are linked to low bone mass caused by bone marrow inflammation in male mice

Skeletal muscle proteome differs between young APOE3 and APOE4 targeted replacement mice in a sex-dependent manner

Introduction

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for Alzheimer's disease (AD), yet it's unclear how this allele mediates risk. APOE4 carriers experience reduced mobility and faster decline in muscle strength, suggesting skeletal muscle involvement. Mitochondria are critical for muscle function and although we have reported defects in muscle mitochondrial respiration during early cognitive decline, APOE4-mediated effects on muscle mitochondria are unknown.

Methods

Here, we sought to determine the impact of APOE4 on skeletal muscle bioenergetics using young, male and female APOE3 (control) and APOE4 targeted replacement mice (n = 8 per genotype/sex combination). We examined the proteome, mitochondrial respiration, fiber size, and fiber-type distribution in skeletal muscle.

Results

We found that APOE4 alters mitochondrial pathway expression in young mouse muscle in a sex-dependent manner without affecting respiration and fiber size or composition relative to APOE3. In both sexes, the expression of mitochondrial pathways involved in electron transport, ATP synthesis, and heat production by uncoupling proteins and mitochondrial dysfunction significantly differed between APOE4 and APOE3 muscle. For pathways with predicted direction of activation, electron transport and oxidative phosphorylation were upregulated while mitochondrial dysfunction and sirtuin signaling were downregulated in female APOE4 vs. APOE3 muscle. In males, sulfur amino acid metabolism was upregulated in APOE4 vs. APOE3 muscle.

Discussion

This work highlights early involvement of skeletal muscle in a mouse model of APOE4-linked AD, which may contribute to AD pathogenesis or serve as a biomarker for brain health.

Brown fat-specific mitoribosomal function is crucial for preventing cold exposure-induced bone loss

This study examines the interplay between ambient temperature, brown adipose tissue (BAT) function, and bone metabolism, emphasizing the effects of cold exposure and BAT mitochondrial activity on bone health. Utilizing ovariectomized (OVX) mice to model primary osteoporosis and BAT-specific mitochondrial dysfunction (BKO) mice, we evaluated the impact of housing temperature on bone density, immune modulation in bone marrow, and the protective role of BAT against bone loss. Cold exposure was found to universally reduce bone mass, enhance osteoclastogenesis, and alter bone marrow T-cell populations, implicating the immune system in bone remodeling under cold stress. The thermogenic function of BAT, driven by mitochondrial oxidative phosphorylation, was crucial in protecting against bone loss. Impaired BAT function, through surgical removal or mitochondrial dysfunction, exacerbated bone loss in cold environments, highlighting BAT's metabolic role in maintaining bone health. Furthermore, cold-induced changes in BAT function led to systemic metabolic shifts, including elevated long-chain fatty acids, which influenced osteoclast differentiation and activity. These findings suggest a systemic mechanism connecting environmental temperature and BAT metabolism with bone physiology, providing new insights into the metabolic and environmental determinants of bone health. Future research could lead to novel bone disease therapies targeting these pathways.

Exploring mechanisms of insulin action and strategies to treat diabetes

Insulin is a hormone that positively regulates anabolism and cell growth, whereas diabetes mellitus is a disease characterized by hyperglycemia associated with impaired insulin action. My colleagues and I have elucidated multifaceted insulin action in various tissues mainly by means of model mice. In the liver, insulin regulates endoplasmic reticulum (ER) stress response during feeding, whereas ER stress 'response failure' contributes to the development of steatohepatitis comorbid with diabetes. Not only the liver but also the proximal tubules of the kidney are important in the regulation of gluconeogenesis, and we revealed that insulin suppresses gluconeogenesis in accordance with absorbed glucose in the latter tissue. In skeletal muscle, another important insulin-targeted tissue, impaired insulin/IGF-1 signaling leads not only to sarcopenia, an aging-related disease of skeletal muscle, but also to osteopenia and shorter longevity. Aging is regulated by adipokines as well, and it should be considered that aging could be accelerated by 'imbalanced adipokines' in patients with a genetic background of progeria. Moreover, we reported the effects of intensive multifactorial intervention on diabetic vascular complications and mortality in patients with type 2 diabetes in a large-scale clinical trial, the J-DOIT3, and the results of subsequent sub-analyses of renal events and fracture events. Various approaches of research enable us of endocrinologists to elucidate the physiology of hormone signaling, the mechanisms underlying the development of endocrine diseases, and the appropriate treatment measures. These approaches also raise fundamental questions, but addressing them in an appropriate manner will surely contribute to the further development of endocrinology.

Crosstalk between muscle and bone

Clinical studies revealed a relationship between osteoporosis and sarcopenia. Based on this background, crosstalk between muscle and bone has emerged as a novel research field in the past decade. Among the interactions that occur between muscle and bone, humoral factors, such as osteokines and myokines, affect distant muscles and bones, respectively. Recent studies proposed several important myokines that have an impact on bone, such as myostatin and irisin. Signaling by these myokines has potential as a target for drug development and biomarkers for exercise. Mechanical stress, endocrine disorders, and chronic kidney disease partly affect bone through various myokines in crosstalk between muscle and bone. Moreover, the involvement of extracellular vesicles from bone or muscle as communication tools in the interactions between muscle and bone was recently proposed. Further clinical studies are needed to clarify the significance of myokine regulation under physiological and pathophysiological states in humans.

Differences in Type 2 Fiber Composition in the Vastus Lateralis and Gluteus Maximus of Patients with Hip Fractures

BACKGRUOUND

Aging leads to sarcopenia, which is characterized by reduced muscle mass and strength. Many factors, including altered muscle protein turnover, diminished neuromuscular function, hormonal changes, systemic inflammation, and the structure and composition of muscle fibers, play a crucial role in age-related muscle decline. This study explored differences in muscle fiber types contributing to overall muscle function decline in aging, focusing on individuals with hip fractures from falls.

METHODS

A pilot study at Chungnam National University Hospital collected muscle biopsies from hip fracture patients aged 20 to 80 undergoing surgical treatment. Muscle biopsies from the vastus lateralis and gluteus maximus were obtained during hip arthroplasty or internal fixation. Handgrip strength, calf and thigh circumference, and bone mineral density were evaluated in individuals with hip fractures from falls. We analyzed the relationships between each clinical characteristic and muscle fiber type.

RESULTS

In total, 26 participants (mean age 67.9 years, 69.2% male) were included in this study. The prevalence of sarcopenia was 53.8%, and that of femoral and lumbar osteoporosis was 19.2% and 11.5%, respectively. Vastus lateralis analysis revealed an age-related decrease in type IIx fibers, a higher proportion of type IIa fibers in women, and an association between handgrip strength and type IIx fibers in men. The gluteus maximus showed no significant correlations with clinical parameters.

CONCLUSION

This study identified complex associations between age, sex, handgrip strength, and muscle fiber composition in hip fracture patients, offering insights crucial for targeted interventions combating age-related muscle decline and improving musculoskeletal health.

Exploring mechanisms underlying diabetes comorbidities and strategies to prevent vascular complications

It is important to prevent not only diabetic complications but also diabetic comorbidities in diabetes care. We have elucidated multifaceted insulin action in various tissues mainly by means of model mice, and it was revealed that insulin regulates endoplasmic reticulum (ER) stress response during feeding, whereas ER stress 'response failure' contributes to the development of steatohepatitis, one of the major diabetic comorbidities. Insulin regulates gluconeogenesis not only in the liver but also in the proximal tubules of the kidney, which is also suppressed by reabsorbed glucose in the latter. In skeletal muscle, another important insulin-targeted tissue, impaired insulin/IGF-1 signaling leads not only to sarcopenia, an aging-related disease, but also to bone loss and shorter longevity. Aging is regulated by adipokines as well, and it is deemed to be accelerated by 'imbalanced adipokines' in combination with genetic background of progeria. Moreover, we reported effects of intensive multifactorial intervention on diabetic complications and mortality in patients with type 2 diabetes in a large-scale clinical trial, the J-DOIT3, followed by reports of subsequent sub-analyses of renal events and fracture events. Various approaches to elucidate the mechanisms underlying the development of diabetes and how it should be treated are expected to help us improve diabetes management.

Associations of Serum CXCL12α and CK Levels with Skeletal Muscle Mass in Older Adults

Sarcopenia, a condition characterized by gradual loss of skeletal muscle mass and function, is a complex diagnosis; the decisive criterion in this diagnosis is the measurement of appendicular skeletal muscle index (ASMI). To identify potential serum markers predictive of sarcopenia in older adults, we evaluated correlations between ASMI, clinical data, and 34 serum inflammation markers in 80 older adults. Pearson's correlation analyses confirmed that ASMI was positively correlated with nutritional status (p = 0.001) and serum creatine kinase (CK) (p = 0.019) but negatively correlated with serum CXCL12α (p = 0.023), a chemoattractant for muscle stem cells. In the case group, ASMI was negatively correlated with serum interleukin (IL)-7 (p = 0.024), a myokine expressed and secreted from skeletal muscle cells in vitro. Multivariate binary logistic regression analyses identified four risk factors for sarcopenia in our study: advanced age (p = 0.012), malnutrition (p = 0.038), low serum CK levels (p = 0.044), and high serum CXCL12α levels (p = 0.029). Low CK and high CXCL12α levels serve as combinatorial serum markers of sarcopenia in older adults. The linear correlation between ASMI and CXCL12α levels may facilitate the development of new regression models for future studies on sarcopenia.

Prognostic value of pretreatment skeletal muscle index in pancreatic carcinoma patients: A meta-analysis

BACKGROUND

The association between pretreatment skeletal muscle index (SMI) and long-term survival of pancreatic carcinoma patients remains unclear up to now.

METHODS

The PubMed, Web of Science and EMBASE databases were searched up to March 1, 2022 for relevant studies. The primary and secondary outcomes were overall survival and progression-free survival, respectively. The hazard ratios (HRs) and 95% confidence intervals (CIs) were combined to assess the relationship between pretreatment SMI and prognosis of pancreatic carcinoma patients. All statistical analysis was conducted by STATA 15.0 software.

RESULTS

Twenty retrospective studies involving 3765 patients were included. The pooled results demonstrated that lower pretreatment SMI was significantly related to poorer overall survival (HR = 1.42, 95% CI: 1.25-1.62, P < .001) and progression-free survival (HR = 1.41, 95% CI: 1.08-1.84, P = .012). Besides subgroup analysis based on the treatment (non-surgery vs surgery) and tumor stage (advanced vs early stage) showed similar results.

CONCLUSION

Pretreatment SMI could serve as a promising and reliable prognostic factor for pancreatic carcinoma patients and lower pretreatment SMI predicted worse prognosis.

Exosome-based bone-targeting drug delivery alleviates impaired osteoblastic bone formation and bone loss in inflammatory bowel diseases

Systematic bone loss is commonly complicated with inflammatory bowel diseases (IBDs) with unclear pathogenesis and uncertain treatment. In experimental colitis mouse models established by dextran sulfate sodium and IL-10 knockout induced with piroxicam, bone mass and quality are significantly decreased. Colitis mice demonstrate a lower bone formation rate and fewer osteoblasts in femur. Bone marrow mesenchymal stem/stromal cells (BMSCs) from colitis mice tend to differentiate into adipocytes rather than osteoblasts. Serum from patients with IBD promotes adipogenesis of human BMSCs. RNA sequencing reveals that colitis downregulates Wnt signaling in BMSCs. For treatment, exosomes with Golgi glycoprotein 1 inserted could carry Wnt agonist 1 and accumulate in bone via intravenous administration. They could alleviate bone loss, promote bone formation, and accelerate fracture healing in colitis mice. Collectively, BMSC commitment in inflammatory microenvironment contributes to lower bone quantity and quality and could be rescued by redirecting differentiation toward osteoblasts through bone-targeted drug delivery.

Prognostic role of pretreatment skeletal muscle index in gastric cancer patients: A meta-analysis

Background: The association between pretreatment skeletal muscle index (SMI) and long-term survival of gastric cancer patients remains unclear up to now. The aim of this meta-analysis was to identify the prognostic value of pretreatment SMI in gastric cancer. Methods: The PubMed, EMBASE and Web of Science electronic databases were searched up to 5 June 2022 for relevant studies. The primary outcome was overall survival (OS) and the second outcomes were disease-free survival (DFS) and cancer-specific survival (CSS). The hazard ratios (HRs) and 95% confidence intervals (CIs) were combined to assess the relationship between pretreatment SMI and survival of gastric cancer patients. All statistical analyses were conducted by STATA 15.0 software. Results: A total of 31 retrospective studies involving 12,434 patients were enrolled in this meta-analysis. The pooled results demonstrated that lower pretreatment was significantly associated with poorer OS (HR = 1.53, p < 0.001). Besides, lower pretreatment SMI was also related with worse DFS (HR = 1.39, p < 0.001) and CSS (HR = 1.96, p < 0.001). Conclusion: Pretreatment SMI was significantly associated with prognosis of gastric cancer patients and lower SMI predicted worse survival. However, more prospective high-quality studies are still needed to verify our findings.

Chronic whole body vibration ameliorates hippocampal neuroinflammation, anxiety-like behavior, memory functions and motor performance in aged male rats dose dependently

Whole body vibration (WBV) is a form of passive exercise by the stimulation of mechanical vibration platform. WBV has been extensively investigated through clinical studies with main focus on the musculoskeletal system. However, pre-clinical data in the context of behavior, memory and motor functions with aged rodents are limited. The aim of this experiment was to investigate the dose dependent effects of a five weeks long WBV intervention with an aged animal model including anxiety-related behavior, memory and motor functions, as well as markers of (neuro)inflammation. Male Wistar rats (18 months) underwent 5 or 20 min daily vibration exposure or pseudo-treatment (i.e.: being subjected to the same environmental stimuli for 5 or 20 min, but without exposure to vibrations) 5 times per week. After 5 weeks treatment, cognitive functions, anxiety-like behavior and motor performance were evaluated. Finally, brain tissue was collected for immunohistological purposes to evaluate hippocampal (neuro)inflammation. Animals with 20 min daily session of WBV showed a decrease in their anxiety-like behavior and improvement in their spatial memory. Muscle strength in the grip hanging test was only significantly improved by 5 min daily WBV treatments, whereas motor coordination in the balance beam test was not significantly altered. Microglia activation showed a significant decrease in the CA1 and Dentate gyrus subregions by both dose of WBV. In contrast, these effects were less pronounced in the CA3 and Hilus subregions, where only 5 min dose showed a significant effect on microglia activation. Our results indicate, that WBV seems to be a comparable strategy on age-related anxiety, cognitive and motor decline, as well as alleviating age-related (neuro)inflammation.