Biology subjects

Ajayi, P. T.

Publications and source records attributed to Ajayi, P. T..

5 recordsLinked to original sources

bioRxiv2024

Changes in Myofibril Size, Shape, and Network Connectivity in Aging Muscle

Across normal aging, striated muscles undergo structural remodeling associated with loss of force production. However, it is unknown how the organization of contractile myofibrillar networks, linked to their efficiency, is modified during aging. Using serial block-face scanning electron microscopy (SBF-SEM), we assess myofibril size, shape, and connectivity across different muscle types in young and geriatric mice and humans. Regardless of skeletal muscle fiber type in mice, age was associated with increased myofibrillar connectivity, with 24 months of age, as compared to 3 months, displaying more sarcomere branches. Distinctive age-related trends in myofibril size and shape were observed among each muscle type. Notably, there was a decrease in myofibril circularity from 3 months of age to 24 months of age in the gastrocnemius muscles of mice, contrasting with an increase in circularity in the soleus muscles during the same time frame. Additionally, while the soleus myofibrils in an aged cohort had a higher cross-sectional area, a reduction was observed in the gastrocnemius muscles. Cardiac muscles displayed no changes in sarcomere connectivity from 3 months to 24 months, although myofibril circularity and cross-sectional area were increased during this time. In human vastus lateralis muscles, sarcomere branching was positively correlated with advanced age. However, there were no consistent changes in myofibril size or shape across a wide age range from 16 to 68 years old. Overall, these data suggest that aging is associated with increased connectivity of the contractile networks within mammalian skeletal muscle. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/615981v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@1b06d92org.highwire.dtl.DTLVardef@1e99c7eorg.highwire.dtl.DTLVardef@2151b3org.highwire.dtl.DTLVardef@17ac3f7_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

Human Heart Failure Alters Mitochondria and Fiber 3D Structure Triggering Metabolic Shifts

This study, utilizing SBF-SEM, reveals structural alterations in mitochondria and myofibrils in human heart failure (HF). Mitochondria in HF show changes in structure, while myofibrils exhibit increased cross-sectional area and branching. Metabolomic and lipidomic analyses indicate concomitant dysregulation in key pathways. The findings underscore the need for personalized treatments considering individualized structural changes in HF.

physiology↗

bioRxiv2022

Mitochondrial Network Configuration Influences Sarcomere and Myosin Filament Structure in Striated Muscles

Sustained muscle contraction occurs through interactions between actin and myosin filaments within sarcomeres and requires a constant supply of adenosine triphosphate (ATP) from nearby mitochondria. However, it remains unclear how different physical configurations between sarcomeres and mitochondria alter the energetic support for contractile function. Here, we show that sarcomere cross-sectional area (CSA) varies along its length in a cell type-dependent manner where the reduction in Z-disk CSA relative to the sarcomere center is closely coordinated with mitochondrial network configuration in flies, mice, and humans. Further, we find myosin filaments near the sarcomere periphery are curved relative to interior filaments with greater curvature for filaments near mitochondria compared to sarcoplasmic reticulum. Finally, we demonstrate smaller myosin filament lattice spacing at filament ends than filament centers in a cell type-dependent manner. These data suggest both sarcomere structure and myofilament interactions are influenced by the location and orientation of mitochondria within muscle cells.

cell biology↗

bioRxiv2021

An Evolutionarily Conserved Regulatory Pathway of Muscle Mitochondrial Network Organization

Mitochondrial networks provide coordinated energy distribution throughout muscle cells. However, pathways specifying mitochondrial network-type separately from contractile fiber-type remain unclear. Here, we show that natural energetic demands placed on Drosophila melanogaster muscles yield native cell-types among which contractile and mitochondrial network-types are regulated independently. Proteomic analyses of indirect flight, jump, and leg muscles together with muscles misexpressing known fiber-type specification factor salm identified transcription factors H15 and cut as potential mitochondrial network regulators. We demonstrate H15 operates downstream of salm regulating flight muscle contractile and mitochondrial network-type. Conversely, H15 regulates mitochondrial network configuration but not contractile type in jump and leg muscles. Further, we find that cut regulates salm expression in flight muscles and mitochondrial network configuration in leg muscles. These data indicate cell type-specific regulation of muscle mitochondrial network organization separately from contractile type, mitochondrial content, and mitochondrial size through an evolutionarily conserved pathway involving cut, salm, and H15.

cell biology↗

bioRxiv2021

Regulation of the Evolutionarily Conserved Muscle Myofibrillar Matrix by Cell Type Dependent and Independent Mechanisms

Skeletal muscles play a central role in human movement through forces transmitted by contraction of the sarcomere. We recently showed that mammalian sarcomeres are connected through frequent branches forming a singular, mesh-like myofibrillar matrix. However, the extent to which myofibrillar connectivity is evolutionarily conserved as well as mechanisms which regulate the specific architecture of sarcomere branching remain unclear. Here, we demonstrate the presence of a myofibrillar matrix in the tubular, but not indirect flight (IF) muscles within Drosophila melanogaster. Moreover, we find that loss of transcription factor H15 increases sarcomere branching frequency in the tubular jump muscles, and we show that sarcomere branching can be turned on in IF muscles by salm-mediated conversion to tubular muscles. Finally, we demonstrate that neurochondrin knockdown results in myofibrillar connectivity in IF muscles without conversion to tubular muscles. These data indicate an evolutionarily conserved myofibrillar matrix regulated by both cell-type dependent and independent mechanisms.

cell biology↗