
==== Front
bioRxiv
BIORXIV
bioRxiv
2692-8205
Cold Spring Harbor Laboratory

10.1101/2024.08.26.609684
preprint
1
Article
Actin Polymerization Status Regulates Tendon Homeostasis through Myocardin-Related Transcription Factor-A
West Valerie C.
Owen Kaelyn
Inguito Kameron L.
Ebron Karl Matthew M.
Reiner Tori
Mirack Chloe E.
Le Christian
Marqueti Rita de Cassia
Snipes Steven
Mousavizadeh Rouhollah
Elliott Dawn M. http://orcid.org/0000-0003-4792-1029

Parreno Justin http://orcid.org/0000-0001-5277-6255

26 8 2024
2024.08.26.609684https://creativecommons.org/licenses/by-nc-nd/4.0/ This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which allows reusers to copy and distribute the material in any medium or format in unadapted form only, for noncommercial purposes only, and only so long as attribution is given to the creator.
http://biorxiv.org/lookup/doi/10.1101/2024.08.26.609684
nihpp-2024.08.26.609684.pdf
Abstract

The actin cytoskeleton is a potent regulator of tenocyte homeostasis. However, the mechanisms by which actin regulates tendon homeostasis are not entirely known. This study examined the regulation of tenocyte molecule expression by actin polymerization via the globular (G-) actin-binding transcription factor, myocardin-related transcription factor-a (MRTF). We determined that decreasing the proportion of G-actin in tenocytes by treatment with TGFβ1 increases nuclear MRTF. These alterations in actin polymerization and MRTF localization coincided with favorable alterations to tenocyte gene expression. In contrast, latrunculin A increases the proportion of G-actin in tenocytes and reduces nuclear MRTF, causing cells to acquire a tendinosis-like phenotype. To parse out the effects of F-actin depolymerization from regulation by MRTF, we treated tenocytes with cytochalasin D. Similar to latrunculin A treatment, exposure of cells to cytochalasin D increases the proportion of G-actin in tenocytes. However, unlike latrunculin A treatment, cytochalasin D increases nuclear MRTF. Compared to latrunculin A treatment, cytochalasin D led to opposing effects on the expression of a subset of genes. The differential regulation of genes by latrunculin A and cytochalasin D suggests that actin signals through MRTF to regulate a specific subset of genes. By targeting the deactivation of MRTF through the inhibitor CCG1423, we verify that MRTF regulates Type I Collagen, Tenascin C, Scleraxis, and α-smooth muscle actin in tenocytes. Actin polymerization status is a potent regulator of tenocyte homeostasis through the modulation of several downstream pathways, including MRTF. Understanding the regulation of tenocyte homeostasis by actin may lead to new therapeutic interventions against tendinopathies, such as tendinosis.
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