{"title":"Changes in serial sarcomere number of five hindlimb muscles across adult aging in rats.","authors":"Avery Hinks, Geoffrey A Power","doi":"10.1159/000546887","DOIUrl":null,"url":null,"abstract":"<p><strong>Introduction: </strong>The age-associated loss of muscle mass is partly accounted for by a reduction in muscle fascicle length (FL). Studies on rodents have confirmed this reduced FL is driven by a loss of sarcomeres aligned in series (serial sarcomere number; SSN) along a muscle. However, studies on rodents have focused primarily on rat plantar flexor SSN at two aging timepoints, leaving an incomplete view of age-related changes in SSN. Hence, this study investigated SSN as a contributor to the age-related loss of muscle mass in five hindlimb muscles across four aging timepoints in rats.</p><p><strong>Methods: </strong>The soleus, medial gastrocnemius (MG), plantaris, tibialis anterior (TA), and vastus lateralis (VL) were obtained from 5 young (8 months), 5 middle-aged (20 months), 5 old (32 months), and 5 very old (36 months) male F344BN rats. After fixation of muscles in formalin and digestion in nitric acid, fascicles were teased out end-to-end to measure FL. SSN was determined by dividing FL by sarcomere length measured via laser diffraction. Muscle wet weight, anatomical cross-sectional area (ACSA), and physiological cross-sectional area (PCSA) were also determined for insight on age-related losses of whole-muscle mass and in-parallel muscle morphology.</p><p><strong>Results: </strong>Age-related SSN loss was apparent after middle age for all muscles, with the plantaris showing the smallest (8%) and the VL the greatest (21%) differences between age groups. The MG and VL appeared to plateau in their SSN loss by 32 months, while the soleus and TA demonstrated continued decline from 32 to 36 months. In all muscles, an age-related lower SSN evidently contributed in part to the smaller muscle mass, alongside less contractile tissue in parallel (indicated by ACSA and PCSA).</p><p><strong>Conclusion: </strong>As SSN is closely tied to biomechanical function, these findings present SSN as a distinct target for improving muscle performance in older adults.</p>","PeriodicalId":12662,"journal":{"name":"Gerontology","volume":" ","pages":"1-23"},"PeriodicalIF":3.1000,"publicationDate":"2025-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Gerontology","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1159/000546887","RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GERIATRICS & GERONTOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Introduction: The age-associated loss of muscle mass is partly accounted for by a reduction in muscle fascicle length (FL). Studies on rodents have confirmed this reduced FL is driven by a loss of sarcomeres aligned in series (serial sarcomere number; SSN) along a muscle. However, studies on rodents have focused primarily on rat plantar flexor SSN at two aging timepoints, leaving an incomplete view of age-related changes in SSN. Hence, this study investigated SSN as a contributor to the age-related loss of muscle mass in five hindlimb muscles across four aging timepoints in rats.
Methods: The soleus, medial gastrocnemius (MG), plantaris, tibialis anterior (TA), and vastus lateralis (VL) were obtained from 5 young (8 months), 5 middle-aged (20 months), 5 old (32 months), and 5 very old (36 months) male F344BN rats. After fixation of muscles in formalin and digestion in nitric acid, fascicles were teased out end-to-end to measure FL. SSN was determined by dividing FL by sarcomere length measured via laser diffraction. Muscle wet weight, anatomical cross-sectional area (ACSA), and physiological cross-sectional area (PCSA) were also determined for insight on age-related losses of whole-muscle mass and in-parallel muscle morphology.
Results: Age-related SSN loss was apparent after middle age for all muscles, with the plantaris showing the smallest (8%) and the VL the greatest (21%) differences between age groups. The MG and VL appeared to plateau in their SSN loss by 32 months, while the soleus and TA demonstrated continued decline from 32 to 36 months. In all muscles, an age-related lower SSN evidently contributed in part to the smaller muscle mass, alongside less contractile tissue in parallel (indicated by ACSA and PCSA).
Conclusion: As SSN is closely tied to biomechanical function, these findings present SSN as a distinct target for improving muscle performance in older adults.
期刊介绍：
In view of the ever-increasing fraction of elderly people, understanding the mechanisms of aging and age-related diseases has become a matter of urgent necessity. ''Gerontology'', the oldest journal in the field, responds to this need by drawing topical contributions from multiple disciplines to support the fundamental goals of extending active life and enhancing its quality. The range of papers is classified into four sections. In the Clinical Section, the aetiology, pathogenesis, prevention and treatment of agerelated diseases are discussed from a gerontological rather than a geriatric viewpoint. The Experimental Section contains up-to-date contributions from basic gerontological research. Papers dealing with behavioural development and related topics are placed in the Behavioural Science Section. Basic aspects of regeneration in different experimental biological systems as well as in the context of medical applications are dealt with in a special section that also contains information on technological advances for the elderly. Providing a primary source of high-quality papers covering all aspects of aging in humans and animals, ''Gerontology'' serves as an ideal information tool for all readers interested in the topic of aging from a broad perspective.
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