Counteracting sarcopenia: the role of IGF-1 isoforms

Ablation of specific insulin-like growth factor I forms reveals the importance of cleavage for regenerative capacity and glycosylation for skeletal muscle storage

Insulin-like growth factor-I (IGF-I) facilitates mitotic and anabolic actions in all tissues. In skeletal muscle, IGF-I can promote growth and resolution of damage by promoting satellite cell proliferation and differentiation, suppressing inflammation, and enhancing fiber formation. While the most well-characterized form of IGF-I is the mature protein, alternative splicing and post-translational modification complexity lead to several additional forms of IGF-I. Previous studies showed muscle efficiently stores glycosylated pro-IGF-I. However, non-glycosylated forms display more efficient IGF-I receptor activation in vitro, suggesting that the removal of the glycosylated C terminus is a necessary step to enable increased activity. We employed CRISPR-Cas9 gene editing to ablate IGF-I glycosylation sites (2ND) or its cleavage site (3RA) in mice to determine the necessity of glycosylation or cleavage for IGF-I function in postnatal growth and during muscle regeneration. 3RA mice had the highest circulating and muscle IGF-I content, whereas 2ND mice had the lowest levels compared to wild-type mice. After weaning, 4-week-old 2ND mice exhibited higher body and skeletal muscle mass than other strains. However, by 16 weeks of age, muscle and body size differences disappeared. Even though 3RA mice had more IGF-I stored in muscle in homeostatic conditions, regeneration was delayed after cardiotoxin-induced injury, with prolonged necrosis most evident at 5 days post injury (dpi). In contrast, 2ND displayed improved regeneration with reduced necrosis, and greater fiber size and muscle mass at 11 and 21 dpi. Overall, these results demonstrate that while IGF-I glycosylation may be important for storage, cleavage is needed to enable IGF-I to be used for efficient activity in postnatal growth and following acute injury.

Ophiocephalus striatus Extract Supplementation Decreases Serum IL-6 Levels in Older People with Sarcopenia-A Single-Center Experience

Sarcopenia, a condition characterized by muscle loss and decreased function in older adults, is a growing public health concern. This study aimed to investigate the effects of Ophiocephalus striatus extract on insulin-like growth factor-1 serum, interleukin-6 serum levels, and sarcopenia-related parameters in older adults with sarcopenia. This double-blind randomized controlled trial included 80 older adults with sarcopenia. Participants were randomly assigned to receive Ophiocephalus striatus extract or a placebo for two weeks. The IGF-1 serum and IL-6 serum levels were assessed as primary outcomes. The Ophiocephalus striatus extract intervention resulted in a significant reduction in serum IL-6 levels. Although the IGF-1 levels did not show significant changes, there was an increase for the intervention group. This study demonstrated that a 2-week intervention with Ophiocephalus striatus extract positively impacted the serum IL-6 levels in older adults with sarcopenia. While the IGF-1 levels did not change significantly in this short intervention period, the observed improvements in IGF-1, calf circumference, muscle mass, and muscle strength are promising. The findings suggest that Ophiocephalus striatus extract may offer a valuable intervention for managing sarcopenia, particularly in regions with abundant Ophiocephalus striatus production, such as South Sumatera. This study was registered with trial number NCT05869383.

Construction of Plasmid DNA Expressing Two Isoforms of Insulin-Like Growth Factor-1 and Its Effects on Skeletal Muscle Injury Models

Insulin-like growth factor-1 (IGF-1) plays a significant role in the development of various organs, and several studies have suggested that IGF-1 isoforms, IGF-1 Ea and IGF-1 Ec, are expressed in skeletal muscle to control its growth. In this study, we designed a novel nucleotide sequence, IGF-1-X10, consisting of IGF-1 exons and introns to simultaneously express both IGF-1 Ea and IGF-1 Ec. When transfected into human cells, the expression of both isoforms was observed at the transcript and protein levels. In an animal study, intramuscular injection of plasmid DNA comprising IGF-1-X10 induced the expression of IGF-1 Ea and IGF-1 Ec, leading to the production of functional IGF-1 protein. Finally, the efficacy of this plasmid DNA was tested in a cardiotoxin (CTX)-mediated muscle injury model and age-related muscle atrophy model. We found that IGF-1-X10 increased the muscle mass and controlled several key factors involved in the muscle atrophy program in both models. Taken together, these data suggest that IGF-1-X10 may be utilized in the form of gene therapy for the treatment of various muscle diseases related to IGF-1 deficiency.

Extra Virgin Olive Oil (EVOO), a Mediterranean Diet Component, in the Management of Muscle Mass and Function Preservation

Aging results in a progressive decline in skeletal muscle mass, strength and function, a condition known as sarcopenia. This pathological condition is due to multifactorial processes including physical inactivity, inflammation, oxidative stress, hormonal changes, and nutritional intake. Physical therapy remains the standard approach to treat sarcopenia, although some interventions based on dietary supplementation are in clinical development. In this context, thanks to its known anti-inflammatory and antioxidative properties, there is great interest in using extra virgin olive oil (EVOO) supplementation to promote muscle mass and health in sarcopenic patients. To date, the molecular mechanisms responsible for the pathological changes associated with sarcopenia remain undefined; however, a complete understanding of the signaling pathways that regulate skeletal muscle protein synthesis and their behavior during sarcopenia appears vital for defining how EVOO might attenuate muscle wasting during aging. This review highlights the main molecular players that control skeletal muscle mass, with particular regard to sarcopenia, and discusses, based on the more recent findings, the potential of EVOO in delaying/preventing loss of muscle mass and function, with the aim of stimulating further research to assess dietary supplementation with EVOO as an approach to prevent or delay sarcopenia in aging individuals.

Serum IGF-1 levels are associated with sarcopenia in elderly men but not in elderly women

BACKGROUND

Sarcopenia is an age-associated decline in muscle mass that negatively affects the metabolic rate, strength, and function of the body and ultimately leads to a decrease in quality of life. Insulin-like growth factor 1 (IGF-1) is a modulator of muscle mass and muscle function. There is evidence that IGF-1 is related to the appendicular skeletal muscle mass index (ASMI) and grip strength. The aim of this study was to explore the relationship between serum IGF-1 levels and sarcopenia in older people.

METHODS

In this cross-sectional survey of 984 people older than 60 years old, we used the 2019 criteria of the Asian Working Group for Sarcopenia (AWGS) to define sarcopenia. We collected demographic variables, measured ASMI and grip strength, and detected serum IGF-1 data. The levels of serum IGF-1 were separated into quintiles (Q1-Q5).

RESULTS

Adjusted for age, education level, smoking, number of diseases and BMI, the multivariable linear regression analysis revealed that serum IGF-1 levels were related to ASMI in elderly men (coefficient = 0.03, 95% CI = 0.02-0.05, P < 0.001) but were not related to their grip strength. There was no significant relationship between serum IGF-1 levels and ASMI or grip strength in elderly women. The multivariable log-binomial regression analysis showed that higher serum IGF-1 levels were associated with a lower prevalence of sarcopenia in elderly men (prevalence ratio (PR) = 0.99, 95% CI = 0.98-1.00, P < 0.05) but not in elderly women.

CONCLUSION

Serum IGF-1 levels were highly correlated with sarcopenia in older men. Further studies are needed to further explore the possible reasons for the observed difference between genders. Serum IGF-1 might predict sarcopenia prevalence in elderly men.

Age-Related Alterations at Neuromuscular Junction: Role of Oxidative Stress and Epigenetic Modifications

With advancing aging, a decline in physical abilities occurs, leading to reduced mobility and loss of independence. Although many factors contribute to the physio-pathological effects of aging, an important event seems to be related to the compromised integrity of the neuromuscular system, which connects the brain and skeletal muscles via motoneurons and the neuromuscular junctions (NMJs). NMJs undergo severe functional, morphological, and molecular alterations during aging and ultimately degenerate. The effect of this decline is an inexorable decrease in skeletal muscle mass and strength, a condition generally known as sarcopenia. Moreover, several studies have highlighted how the age-related alteration of reactive oxygen species (ROS) homeostasis can contribute to changes in the neuromuscular junction morphology and stability, leading to the reduction in fiber number and innervation. Increasing evidence supports the involvement of epigenetic modifications in age-dependent alterations of the NMJ. In particular, DNA methylation, histone modifications, and miRNA-dependent gene expression represent the major epigenetic mechanisms that play a crucial role in NMJ remodeling. It is established that environmental and lifestyle factors, such as physical exercise and nutrition that are susceptible to change during aging, can modulate epigenetic phenomena and attenuate the age-related NMJs changes. This review aims to highlight the recent epigenetic findings related to the NMJ dysregulation during aging and the role of physical activity and nutrition as possible interventions to attenuate or delay the age-related decline in the neuromuscular system.

Inducible Rpt3, a Proteasome Component, Knockout in Adult Skeletal Muscle Results in Muscle Atrophy

The ubiquitin–proteasome system has the capacity to degrade polyubiquitinated proteins and plays an important role in many cellular processes. However, the role of Rpt3, a crucial proteasomal gene, has not been investigated in adult muscles in vivo. Herein, we generated skeletal-muscle-specific Rpt3 knockout mice, in which genetic inactivation of Rpt3 could be induced by doxycycline administration. The Rpt3-knockout mice showed a significant reduction by more than 90% in the expression of Rpt3 in adult muscles. Using this model, we found that proteasome dysfunction in adult muscles resulted in muscle wasting and a decrease in the myofiber size. Immunoblotting analysis showed that the amounts of ubiquitinated proteins were markedly higher in muscles of Rpt3-deficient mice than in those of the control mice. Analysis of the autophagy pathway in the Rpt3-deficient mice showed that the upregulation of LC3II, p62, Atg5, Atg7, and Beclin-1 in protein levels, which supposed to be compensatory proteolysis activation. Our results suggest that the proteasome inhibition in adult muscle severely deteriorates myofiber integrity and results in muscle atrophy.