Biology subjects

Pugh, J. N.

Publications and source records attributed to Pugh, J. N..

3 recordsLinked to original sources

bioRxiv2023

Primary cilia in osteoblasts and osteocytes are required for skeletal development and mechanotransduction

1.Primary cilia have been involved in the development and mechanosensation of various tissue types, including bone. In this study, we explored the mechanosensory role of primary cilia in bone growth and adaptation by examining two cilia specific genes, IFT88 and MKS5, required for proper cilia assembly and function. To analyze the role of primary cilia in osteoblasts, Osx1-GFP:Cre mice were bred with IFT88LoxP/LoxP to generate mice with a conditional knockout of primary cilia in osteoblasts. A significant decrease in body weight was observed in both male (p=0.0048) and female (p=0.0374) conditional knockout (cKO) mice compared to the wild type (WT) controls. The femurs of cKO mice were significantly shorter than that of the WT mice of both male (p=0.0003) and female (p=0.0019) groups. Histological analysis revealed a significant difference in MAR (p=0.0005) and BFR/BS (p<0.0001) between female cKO and WT mice. The BFR/BS of male cKO mice was 58.03% lower compared to WT mice. To further investigate the role of primary cilia in osteocytes, Dmp1-8kb-Cre mice were crossed with MKS5LoxP/LoxP to generate mice with defective cilia in osteocytes. In vivo axial ulnar loading was performed on 16-week-old mice for 3 consecutive days. The right ulnae were loaded for 120 cycles/day at a frequency of 2Hz with a peak force of 2.9N for female mice and 3.2N for male mice. Load-induced bone formation was measured using histomorphometry. The relative values of MS/BS, MAR and BFR/BS (loaded ulnae minus nonloaded ulnae) in male MKS5 cKO mice were decreased by 24.88%, 46.27% and 48.24%, respectively, compared to the controls. In the female groups, the rMS/BS was 52.5% lower, the rMAR was 27.58% lower, and the rBFR/BS was 41.54% lower in MKS5 cKO mice than the WT group. Histological analysis indicated that MKS5 cKO mice showed significantly decreased response to mechanical loading compared to the controls. Taken together, these data highlight a critical role of primary cilia in bone development and mechanotransduction, suggesting that the presence of primary cilia in osteoblasts play an important role in skeletal development, and primary cilia in osteocytes mediate mechanically induced bone formation.

cell biology↗

bioRxiv2023

Muscle fibre size and myonuclear positioning in trained and aged humans

Myonuclear domain (MND) is the theoretical volume of cytoplasm within which a myonucleus is responsible for transcribing DNA. Changes in myonuclear number, organisation, and myonuclear domain size are associated with exercise adaptations and ageing. However, data on satellite cell activation, changes in MND volumes and myonuclear arrangement following exercise are inconsistent. Additionally, whether MNDs and myonuclear arrangement are altered with age remains unclear. The aim of the present investigation was therefore to investigate relationships between age and activity status and myonuclear numbers and organisation. Muscle fibres from younger trained (YT) and older trained (OT) individuals were compared with age-matched untrained counterparts (YU and OU). Serial, optical z-slices were acquired throughout isolated muscle fibres and analysed to give 3D coordinates for myonuclei and muscle fibre dimensions, respectively. As expected, mean cross-sectional area (CSA) (m2) of muscle fibres from OU was 29-42% smaller compared to the other groups. Number of nuclei relative to fibre CSA was 87% greater in OU compared to YU muscle fibres (P < 0.05). Additionally, scaling of myonuclear domain volume with fibre size was altered in older untrained individuals. Myonuclear arrangement, on the other hand, was similar across groups. These data indicate that regular endurance exercise throughout the lifespan may preserve the size of single muscle fibres in older age and maintain the relationship between fibre size and MND volumes. Inactivity, however, may result in reduced muscle fibre size and disrupted relationship between fibre size and MND volumes. Plain Language SummaryIn this study, we examined the relationship between physical activity and the characteristics of muscle fibres in individuals of different age groups. We focused on a concept called the myonuclear domain (MND), which refers to the volume surrounding muscle nuclei or myonuclei that house the genome. We wanted to understand how changes in myonuclear number, organisation, and MND size were influenced by exercise and aging. To do this, we compared muscle fibres from younger trained individuals, older trained individuals, and age-matched untrained individuals. The results showed that the average size of muscle fibres in the untrained older individuals was smaller compared to the other groups. Moreover, the number of nuclei relative to fibre size was significantly higher in the untrained older individuals. However, myonuclear arrangement was similar across all groups. These findings suggest that regular endurance exercise throughout life may help maintain muscle fibre size, myonuclear numbers, MND volumes, and myonuclear organisation in older individuals. Conversely, inactivity can lead to reduced muscle fibre size and disrupted relationship between fibre size and MND volumes. These results have important implications for understanding the effects of exercise and aging on muscle health.

physiology↗

bioRxiv2022

Exercise induces myonuclear remodelling in humans independently of age

Age-related decline in skeletal muscle structure and function can be mitigated by regular exercise. However, the precise mechanisms that govern this are not fully understood. The nucleus plays an active role in translating forces into biochemical signals (mechanotransduction), with nuclear lamina protein Lamin A regulating nuclear shape, nuclear mechanics, and ultimately gene expression. Defective Lamin A expression causes muscle pathologies and premature ageing syndromes, but the roles of nuclear structure and function in physiological ageing and in exercise adaptations remain obscure. Here, we isolated single muscle fibres and carried out detailed morphological and functional analyses on myonuclei from young and older exercise-trained individuals. Strikingly, myonuclei from trained individuals were more spherical, less deformable, and contained a thicker nuclear lamina than untrained individuals. Complementary to this, exercise resulted in increased levels of Lamin A and increased myonuclear stiffness in mice. We conclude that exercise is associated with myonuclear remodelling, independently of age, which may contribute to the preservative effects of exercise on muscle function throughout the lifespan. Key pointsO_LIThe nucleus plays an active role in translating forces into biochemical signals C_LIO_LIMyonuclear aberrations in a group of muscular dystrophies called laminopathies suggest that the shape and mechanical properties of myonuclei are important for maintaining muscle function. C_LIO_LIHere, we present striking differences in myonuclear shape and mechanics associated with exercise, in both young and old humans. C_LIO_LIMyonuclei from trained individuals were more spherical, less deformable, and contained a thicker nuclear lamina than untrained individuals. C_LIO_LIWe conclude that exercise is associated with age-independent myonuclear remodelling, which may help to maintain muscle function throughout the lifespan. C_LI

cell biology↗