The role of Activin A in renal and skeletal muscle pathophysiology

Abstract

Background: Chronic kidney disease (CKD) is a substantial global health concern, impacting 10-15% of the world’s population. CKD increases the risk of hospitalisation, co-morbidity and mortality, and ultimately reduces patient quality of life. Renal fibrosis, and the structural and functional changes that accompany it, is a key step in the pathogenesis of CKD. Intriguingly, the effects of CKD are not limited to the renal system; with muscle wasting common in CKD, which synergistically causes debilitation and reduced patient quality of life. It is necessary to identify new therapeutic targets that effectively ameliorate CKD development and progression, such as those that target renal fibrosis and muscle wasting. Upregulated Activin A, a growth and differentiation factor, has been identified in CKD and CKD-induced muscle wasting. Whilst inhibiting Activin A successfully ameliorates renal fibrosis and muscle wasting in vivo, understanding of its signalling pathways remains elusive, particularly in renal proximal tubule epithelial cells and in endoplasmic reticulum (ER) stress pathways in skeletal muscle cells which may contribute to muscle wasting.

Results: In HK2 cells, Activin A alone or with co-treatment with SB431542 did not alter protein abundance of SMAD2/3 signalling or fibrotic markers, or affect the Activin A concentration present in the media at the conclusion of the experiment. Activin A also did not have a time-dependant effect on these parameters at 6-, 18-, 24- or 48- hours. However, the protein abundance of pSMAD2/3 and fibronectin was significantly increased by TGF-β treatment, and Activin A concentration in the media was significantly elevated 2.35 fold compared to control treatment alone. Interestingly, TGF-β in conjunction with the inhibitor SB431542 ameliorated these increases in both protein expression and concentration of Activin A present in the media. In skeletal muscle cells, protein abundance of UPR markers was not significantly altered by Activin A treatment, however the mRNA expression of ATF4 and XBP1s was significantly downregulated. SUnSET assay did not indicate any significant change to global protein synthesis.

Conclusions and Impact: The data presented in this thesis is one of the first studies to investigate the role of Activin A signalling specifically in human-derived renal proximal tubule cells, a key cell population important in CKD development and progression. It demonstrates an important role of Activin A in proximal tubule cells in response to TGF- β, and also identifies a novel effect on skeletal muscle UPR which may have implications in the understanding of CKD-induced muscle wasting.

Date of Thesis submission	2024
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Kayte Jenkin (Supervisor) & Ben Perry (Supervisor)