Background/Purpose: Systemic Sclerosis (SSc) is an autoimmune disorder characterised by abnormal activation of tissue fibroblasts, resulting in tissue and vascular fibrosis of the skin and internal organs. Aberrant activation of TGFβ signalling plays a central role in the profibrotic fibroblast phenotype. Fibroblasts cultured from SSc skin biopsies maintain their profibrotic activation in vitro. Patients with SSc do not show classic signs of primary aberrant profibrotic activation such as keloid or fibrotic responses to injury, leaving the mechanisms underlying fibroblast activation and tissue fibrosis not completely elucidated. The primary cilium (PC) is a sensory antenna-like organelle on the cell, forming a specialised signalling hub for several pathways involved in tissue homeostasis and response to the extracellular microenvironment. The aim of this study was to investigate the structure of the PC in SSc dermal fibroblasts to determine its potential contribution to SSc pathogenesis.

Methods: Dermal fibroblasts were isolated from forearm skin biopsies of healthy control (HC) and SSc patients. PC were visualised by immunofluorescence with an Acetylated-α-Tubulin antibody followed by confocal microscopy. PC length was quantified from at least 100 PC across 3 independent fields per condition. Fibroblasts were stimulated with TGFβ for 24h or a set time course with increments between 0-24h. SD208 (1µM) was used to inhibit TGFβ Receptor Kinase 1 (TGFβR1), MLN8054 (5µM) was used to inhibit Aurora A Kinase (AURKA), and Tubastatin A (1µM) was used to inhibit Histone Deacetylase 6 (HDAC6).

Results: PC length was normally distributed in both HC and SSc dermal fibroblasts. PC from SSc fibroblasts were on average 45% shorter than HC (2.5 ± 0.6 µm vs 4.6 ± 1.3 µm, respectively (P< 0.0001)). TGFβ treatment significantly reduced the mean PC length in both HC and SSc, reaching around 1.8 µm in both by 24 hours. Time course experiments showed a quicker response to TGFβ in SSc fibroblasts, with PC starting to shorten as soon as 2h vs 6h in HC. Inhibition of TGFβR1 prevented the ability of TGFβ to shorten PC in both, but did not ‘rescue’ SSc fibroblast PC length to that of HC. On the contrary, inhibition of AURKA – a kinase known to be involved in PC disassembly – did not abolish the effect of TGFβ in either cell type. However, AURKA inhibition increased PC length of SSc cells from 2.9 ± 0.4 µm to 4.4 ± 0.9 µm (P< 0.05), without affecting HC PC length, effectively “rescueing” the shortened PC phenotype of SSc cells, increasing PC length, indistinguishable from HC PC. The effect of AURKA was independent of its primary effector, HDAC6, as neither the difference in basal PC length nor the TGFβ effect were rescued by HDAC6 inhibition with Tubastatin A.

Conclusion: PC length is stably reduced in SSc dermal fibroblasts independently of TGFβR1 activity. Inhibition of AURKA in SSc restores “healthy” PC length via an atypical mechanism not involving its primary effector HDAC6. These observations support the notion that the profibrotic activation of dermal fibroblasts in SSc may go beyond a TGFβ-dependent mechanism. Modulation of PC length by AURKA deserves to be further explored as a contributor to profibrotic activation, and a potential therapeutic target for tissue fibrosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/systemic-sclerosis-ssc-dermal-fibroblasts-show-shortened-primary-cilia-due-to-aberrant-aurora-a-kinase-activation-independently-of-transforming-growth-factor-%ce%b2-signalling/