Physiology and pathophysiology of musculoskeletal aging: current research trends and future priorities

Effects of Plant-Based Protein Interventions, with and without an Exercise Component, on Body Composition, Strength and Physical Function in Older Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Maintaining muscle mass, strength, and function is crucial for our aging population. Exercise and dietary protein intake are recommended strategies; however, animal proteins have been the most studied. Plant-based protein sources have lower digestibility and incomplete amino acid profiles. However new innovative plant-based proteins and products may have overcome these issues. Therefore, this systematic review aimed to synthesize the current research and evaluate the effects of plant-based protein interventions compared to placebo on body composition, strength, and physical function in older adults (≥60 years old). The secondary aim was whether exercise improved the effectiveness of plant-based protein on these outcomes. Randomized controlled trials up to January 2023 were identified through Medline, EMBASE, CINAHL, and Cochrane Library databases. Studies contained a plant-protein intervention, and assessed body composition, strength, and/or physical function. Thirteen articles were included, all using soy protein (0.6-60 g daily), from 12 weeks to 1 year. Narrative summary reported positive effects on muscle mass over time, with no significant differences compared to controls (no intervention, exercise only, animal protein, or exercise + animal protein interventions). There was limited impact on strength and function. Meta-analysis showed that plant-protein interventions were comparable to controls, in all outcomes. In conclusion, plant-protein interventions improved muscle mass over time, and were comparable to other interventions, warranting further investigation as an anabolic stimulus in this vulnerable population.

Does Whole-Body Vibration Training Have a Concurrent Effect on Bone and Muscle Health? A Systematic Review and Meta-Analysis

BACKGROUND

Aging results in musculoskeletal disorders, which are a leading cause of disability worldwide. While conventional nonpharmacological treatments have included interventions such as resistance exercise, there are subgroups of people who may be at risk of exercise-related injuries, for example, falls. Whole-body vibration (WBV) is an intervention that helps improve musculoskeletal function and is viable for those with limited mobility.

OBJECTIVES

Whether WBV has a dual effect on bone and muscle conditions remains unknown. We aim to assess the evidence of the effects of WBV on bone and muscle parameters concurrently in older people.

METHODS

Under Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines, a systematic literature search was performed in MEDLINE, EMBASE, EMCARE, and the Cochrane Central Registry of Controlled Trials. The main outcomes were changes in bone and muscle parameters.

RESULTS

Our meta-analysis showed that WBV does not have significant synergistic effects on measured bone (bone mineral density [BMD] in the hip and lumbar spine) and muscle (lean muscle mass and sit-to-stand time) outcomes, compared to controls (i.e., no WBV included).

CONCLUSION

While there were no significant results, the included studies are limited by small sample size and variable intervention protocols and follow-up periods. Further trials should endeavor to measure both bone and muscle outcomes concurrently with a longer follow-up time. Osteoporosis status in participants must also be considered as it is not yet possible to exclude that WBV may have a significant effect on BMD in people with known osteoporosis. WBV does not appear to simultaneously influence bone and muscle health in older people, and future research is required to establish a regimen that may lead to measurable clinical efficacy.

Insulin resistance since early adulthood and appendicular lean mass in middle-aged adults without diabetes: 20 years of the CARDIA study

AIMS

To determine the association between 20-year trajectories in insulin resistance (IR) since young adulthood and appendicular lean mass (ALM) at middle-age in adults without diabetes.

METHODS

A prospective cohort study was designed among young and middle-aged US men (n = 925) and women (n = 1193). Fasting serum glucose and insulin were measured five times in 1985-2005. IR was determined using the homeostasis model assessment (HOMA). ALM was measured in 2005 and ALM adjusted for BMI (ALM/BMI) was the outcome. Sex-specific analyses were performed.

RESULTS

Three HOMA-IR trajectories were identified. Compared to the low-stable group, the adjusted ALM/BMI difference was -0.041 (95% CI: -0.060 to -0.022) and -0.114 (-0.141 to -0.086) in men, and -0.052 (-0.065 to -0.039) and -0.043 (-0.063 to -0.023) in women, respectively, for the medium-increase and high-increase groups. Further adjusting for the treadmill test duration attenuated these estimates to -0.022 (-0.040 to -0.004) and -0.061 (-0.089 to -0.034) in men and -0.026 (-0.038 to -0.014) and -0.007 (-0.026 to 0.012) in women.

CONCLUSIONS

Compared to the low-stable insulin resistance trajectory between early and middle adulthood, the high-increase trajectory was associated with lower ALM/BMI in middle-aged men, but not women, without diabetes, after adjusting for cardiorespiratory fitness.

PABPN1-Dependent mRNA Processing Induces Muscle Wasting

Poly(A) Binding Protein Nuclear 1 (PABPN1) is a multifunctional regulator of mRNA processing, and its expression levels specifically decline in aging muscles. An expansion mutation in PABPN1 is the genetic cause of oculopharyngeal muscle dystrophy (OPMD), a late onset and rare myopathy. Moreover, reduced PABPN1 expression correlates with symptom manifestation in OPMD. PABPN1 regulates alternative polyadenylation site (PAS) utilization. However, the impact of PAS utilization on cell and tissue function is poorly understood. We hypothesized that altered PABPN1 expression levels is an underlying cause of muscle wasting. To test this, we stably down-regulated PABPN1 in mouse tibialis anterior (TA) muscles by localized injection of adeno-associated viruses expressing shRNA to PABPN1 (shPab). We found that a mild reduction in PABPN1 levels causes muscle pathology including myofiber atrophy, thickening of extracellular matrix and myofiber-type transition. Moreover, reduced PABPN1 levels caused a consistent decline in distal PAS utilization in the 3’-UTR of a subset of OPMD-dysregulated genes. This alternative PAS utilization led to up-regulation of Atrogin-1, a key muscle atrophy regulator, but down regulation of proteasomal genes. Additionally reduced PABPN1 levels caused a reduction in proteasomal activity, and transition in MyHC isotope expression pattern in myofibers. We suggest that PABPN1-mediated alternative PAS utilization plays a central role in aging-associated muscle wasting.

PABPN1 is a multifunctional regulator of mRNA processing and its levels are reduced in skeletal muscles from midlife onwards. Reduced PABPN1 levels in a mouse model causes muscle atrophy and muscle fiber switches. We show that PABPN1-regulated muscle atrophy is regulated, in part, by up regulation of Atrogin1 and reduced expression of proteasome genes via an alternative polyadenylation site utilization. This study reveals a functional role for alternative polyadenylation site utilization in muscle atrophy and suggests a role for RNA processing in muscle aging.

Targeting muscle signaling pathways to minimize adverse effects of androgen deprivation

Androgen deprivation therapy (ADT) is a highly effective treatment used in ∼30% of men with prostate cancer. Adverse effects of ADT on muscle are significant with consistent losses in muscle mass. However, effects of ADT on muscle strength and physical function, of most relevance to the patient, are less well understood. This is in part due to the fact that muscle effects of ADT at the cellular, genetic and protein level, critical to the understanding of the pathophysiology of sarcopenia, have come into focus only recently. This review highlights the complexity of androgen-dependent signaling in muscle with an emphasis on recent findings in the regulation of muscle growth and muscle atrophy pathways. Furthermore, the effects of ADT and testosterone on skeletal muscle histology, gene expression and protein transcription are discussed. A better mechanistic understanding of the regulation of muscle mass and function by androgens should not only pave the way for developing targeted promyogenic interventions for men with prostate cancer receiving ADT but also may have wider implications for age-associated sarcopenia in the general population.

Prevalence of musculoskeletal symptoms among agricultural workers in the United States: an analysis of the National Health Interview Survey, 2004-2008

Ergonomic risks from agricultural tasks can compromise musculoskeletal health of workers. This study estimated prevalence of musculoskeletal symptoms in a sample representing almost 2 million US agricultural industry workers. This study used National Health Interview Survey data from 2004 to 2008. Weighted prevalence was calculated by demographic and employment factors. Prevalence ratios were calculated using generalized linear models with the Poisson distribution assumption. Prevalence rates of low back and neck pain in the previous 3 months were 24.3% and 10.5%, respectively, among agricultural workers. Monthly prevalence of joint pain was 17.0% for hips/knees, 9.8% for shoulders, 9.5% for wrists/hands, 5.4% for elbows, and 4.7% for ankles/toes. Agricultural workers had a significantly higher prevalence of shoulder pain than all other industry workers (prevalence ratios [PR] = 1.28, 95% confidence interval [CI]: 1.02-1.61). This study provides detailed national estimates of musculoskeletal symptom prevalence to understand the burden and the need for intervention among agricultural workers.

The aging lung

There are many age-associated changes in the respiratory and pulmonary immune system. These changes include decreases in the volume of the thoracic cavity, reduced lung volumes, and alterations in the muscles that aid respiration. Muscle function on a cellular level in the aging population is less efficient. The elderly population has less pulmonary reserve, and cough strength is decreased in the elderly population due to anatomic changes and muscle atrophy. Clearance of particles from the lung through the mucociliary elevator is decreased and associated with ciliary dysfunction. Many complex changes in immunity with aging contribute to increased susceptibility to infections including a less robust immune response from both the innate and adaptive immune systems. Considering all of these age-related changes to the lungs, pulmonary disease has significant consequences for the aging population. Chronic lower respiratory tract disease is the third leading cause of death in people aged 65 years and older. With a large and growing aging population, it is critical to understand how the body changes with age and how this impacts the entire respiratory system. Understanding the aging process in the lung is necessary in order to provide optimal care to our aging population. This review focuses on the nonpathologic aging process in the lung, including structural changes, changes in muscle function, and pulmonary immunologic function, with special consideration of obstructive lung disease in the elderly.