Timmis, A. J. | bioRxiv Science

bioRxiv2026

Aurora A kinase activation contributes to the fibrotic phenotype in Systemic Sclerosis through primary cilia shortening

BackgroundSystemic sclerosis (SSc) is a severe autoimmune disease characterised by progressive fibrosis driven by fibroblast activation. Primary cilia, key hubs for profibrotic signalling, are markedly shortened in SSc fibroblasts, but the mechanisms underlying this phenotype remain unclear. This study aimed to define the signalling pathways responsible for primary cilia shortening and fibroblast activation in SSc. MethodsPrimary dermal fibroblasts from SSc patients and healthy controls were analysed for cilia incidence and length by immunofluorescence, profibrotic marker expression by qPCR, and contractility using gel contraction assays. Cells were treated with TGF{beta}1 and pharmacological inhibitors targeting AURKA, HDAC6, ROCK2, and Smad3 signalling. CAV1-silenced fibroblasts were used as an in vitro model of SSc. ResultsMaintenance of the constitutively short primary cilia phenotype in SSc fibroblasts did not require active TGF{beta} signalling. However, TGF{beta}1 induced reversible cilia shortening in healthy fibroblasts and further shortened cilia in SSc fibroblasts to a similar final length, mediated by Rho/ROCK2 rather than canonical Smad3-dependent signalling. Constitutive cilia shortening in SSc was driven by aberrant AURKA activity upstream of HDAC6, promoting ciliary disassembly. Pharmacological inhibition of AURKA or HDAC6 selectively elongated cilia in SSc fibroblasts, reduced profibrotic marker expression, and abrogated fibroblast contractility. CAV1-silenced fibroblasts similarly exhibited constitutive cilia shortening that was reversed by AURKA inhibition without affecting healthy cells. ConclusionsAberrant activation of the AURKA/HDAC6 axis maintains short primary cilia and promotes fibroblast activation in SSc. These findings reveal a mechanistic link between cilia morphology and fibrosis and identify AURKA as a potential therapeutic target for SSc-associated tissue remodelling.

cell biology↗

bioRxiv2023

The Hedgehog receptors PTCH1 and PTCH2 exist as active homomeric and heteromeric complexes

With the importance of Hedgehog signalling in embryonic development, tissue homeostasis and disease, understanding the molecular mechanisms of signal transduction is paramount for the design of specific, effective therapeutics. The Hedgehog receptor PTCH1 and the less studied PTCH2 isoform are evolutionarily related to bacterial RND permeases and sterol sensing proteins, which mobilise hydrophobic compounds powered by a cation gradient. Here we demonstrate that, in the active state, PTCH1 and PTCH2 form homomeric and heteromeric complexes that are inhibited by binding of Sonic Hedgehog. We show that PTCH2, unlike PTCH1, appears to have minimal cholesterol transport activity, but that conserved residues involved in cation transport are essential for its function. Heteromeric PTCH1-PTCH2 complexes depend on PTCH1s cholesterol transport capacity, but the cation transport can be provided in trans by PTCH2, suggesting that some deleterious mutations in either isoform can be silenced by formation of heteromers, enhancing the robustness of this signal transduction system. These findings provide the molecular basis for the intriguing behaviour of PTCH2 as semi-redundant and partially overlapping in function with PTCH1 and explain the dominant negative effect of mutations that disrupt the PTCH2 cation transport triad in rare cases of cancer.

biochemistry↗