Biology subjects

Birks, S.

Publications and source records attributed to Birks, S..

4 recordsLinked to original sources

bioRxiv2026

Chronological Aging Stiffens Cells, Alters Mitochondria, and Impairs Mitochondrial Mechanical Responsiveness in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) can differentiate into osteoblasts and adipocytes, play a critical role for maintaining bone homeostasis. Although, aging impairs MSC function and contributes to several complications, the effects of aging on subcellular structure and related gene expression need further investigation. Here we established an in vitro system to study MSCs isolated from bones of 5, 12, and 24 months old mice which showed significantly decreased bone volume and exercise performance with age. RNA sequencing revealed downregulation of genes related to cell-matrix interactions, cell metabolism, and division. Functionally MSCs extracted from 24mo showed significantly increased adipogenesis and reduced osteogenesis compared to 5mo, which was accompanied by reduced levels of cell proliferative marker Ki67 and increased expression of senescence protein p16. Data-driven segmentation of F-actin architecture revealed no cell-wide or nuclei-associated alteration, while 24mo MSCs showed decreased nuclear volume and increased spreading and higher nuclear stiffness compared to 5mo. Mitochondria from 12mo and 24mo showed increased length and volume of fibers when compared to 5mo, which was accompanied by gene expression changes associated with mitochondrial inflammation and oxidative phosphorylation. To test the functional consequences, MSCs were subjected to mechanical stress for 72 hours using 90Hz, 07g low-intensity vibration (LIV). While 5mo MSCs showed a robust fusing of individual mitochondrial fibers, LIV response of 12mo and 24mo MSCs were progressively less, indicating an already stressed mitochondria compromised to mechanical challenge. In summary, this study has established an in vitro assay system, revealing age-associated impairments in differentiation, mitochondrial function, and mechanotransduction capacity.

bioengineering↗

bioRxiv2023

The LINC complex regulates Achilles tendon elastic modulus, Achilles and tail tendon collagen crimp, and Achilles and tail tendon lateral expansion during early postnatal development.

There is limited understanding of how mechanical signals regulate tendon development. The nucleus has emerged as a major regulator of cellular mechanosensation, via the linker of nucleoskeleton and cytoskeleton (LINC) protein complex. Specific roles of LINC in tenogenesis have not been explored. In this study, we investigate how LINC regulates tendon development by disabling LINC-mediated mechanosensing via dominant negative (dn) expression of the Klarsicht, ANC-1, and Syne Homology (KASH) domain, which is necessary for LINC to function. We hypothesized that LINC regulates mechanotransduction in developing tendon, and that disabling LINC would impact tendon mechanical properties and structure in a mouse model of dnKASH. We used Achilles (AT) and tail (TT) tendons as representative energy-storing and limb-positioning tendons, respectively. Mechanical testing at postnatal day 10 showed that disabling the LINC complex via dnKASH significantly impacted tendon mechanical properties and cross-sectional area, and that effects differed between ATs and TTs. Collagen crimp distance was also impacted in dnKASH tendons, and was significantly decreased in ATs, and increased in TTs. Overall, we show that disruption to the LINC complex specifically impacts tendon mechanics and collagen crimp structure, with unique responses between an energy-storing and limb-positioning tendon. This suggests that nuclear mechanotransduction through LINC plays a role in regulating tendon formation during neonatal development.

developmental biology↗

bioRxiv2023

Prrx1-driven LINC complex disruption in vivo does not significantly alter bone properties in 8-week male mice nor after 6-weeks voluntary wheel running

The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex serves to connect the nuclear envelope and the cytoskeleton, influencing cellular processes such as nuclear arrangement, architecture, and mechanotransduction. The role LINC plays in mechanotransduction pathways in bone progenitor cells has been well studied; however, the mechanisms by which LINC complexes govern in vivo bone formation remain less clear. To bridge this knowledge gap, we established a murine model disrupting LINC using transgenic Prx-Cre mice and floxed Tg(CAG-LacZ/EGFP-KASH2) mice. Prx-Cre mice express the Cre recombinase enzyme controlled by the paired-related homeobox gene-1 promoter (Prrx1), a pivotal regulator of skeletal development. Prx-Cre animals have been widely used in the bone field to target bone progenitor cells. Tg(CAG-LacZ/EGFP-KASH2) mice carry a lox-stop-lox flanked LacZ gene allowing for the overexpression of an EGFP-KASH2 fusion protein via cre recombinase mediated deletion of the LacZ cassette. This disrupts endogenous Nesprin-Sun binding in a dominant negative manner disconnecting nesprin from the nuclear envelope. By combining these lines, we generated a Prrx1(+) cell-specific LINC disruption model to study its impact on the developing skeleton and subsequently exercise-induced bone accrual. The findings presented here indicate Prx-driven LINC disruption (PDLD) cells exhibit no change in osteogenic and adipogenic potential compared to controls in vitro nor are there bone quality changes when compared to in sedentary animals at 8 weeks. While PDLD animals displayed increased voluntary running activity andPrrx1(+) cell-specific LINC disruption abolished the exercise-induced increases in osteoid volume and surface after a 6-week exercise intervention, no other changes in bone microarchitecture or mechanical properties were found.

bioengineering↗

bioRxiv2023

Osterix-driven LINC complex disruption in vivo diminishes bone microarchitecture in 8-week male mice but not after 6-week voluntary wheel running

The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex is a crucial connective component between the nuclear envelope and the cytoskeleton involving various cellular processes including nuclear positioning, nuclear architecture, and mechanotransduction. How LINC complexes regulate bone formation in vivo, however, is not well understood. To start bridging this gap, here we created a LINC disruption murine model using transgenic mice expressing Cre recombinase enzyme under the control of the Osterix (Osx-Cre) which is primarily active in pre-osteoblasts and floxed Tg(CAG-LacZ/EGFP-KASH2) mice. Tg(CAG-LacZ/EGFP-KASH2) mice contain a lox-STOP-lox flanked LacZ gene which is deleted upon cre recombination allowing for the overexpression of an EGFP-KASH2 fusion protein. This overexpressed protein disrupts endogenous Nesprin-Sun binding leading to disruption of LINC complexes. Thus, crossing these two lines results in a Osx-driven LINC disruption (ODLD) specific to pre-osteoblasts. In this study, we investigated how this LINC disruption affects exercise induced bone accrual. ODLD cells had decreased osteogenic and adipogenic potential in vitro compared to non-disrupted controls and sedentary ODLD mice showed decreased bone quality at 8-weeks. Upon access to a voluntary running wheel ODLD animals showed increased running time and distance; however, our 6-week exercise intervention did not significantly affect bone microarchitecture and bone mechanical properties.

bioengineering↗