PAK1-dependant mechanotransduction enables myofibroblast nuclear adaptation and chromatin organisation during fibrosis

Myofibroblasts are responsible for scarring and organ stiffness during fibrosis. The scar propagates mechanical signals inducing a radical transformation in myofibroblast cell state linked to an increasingly pro-fibrotic phenotype. Here, we have discovered mechanical stress from progressive scarring induces nuclear softening and de-repression of heterochromatin. The parallel loss of H3K9Me3 enables a permissive state for distinct chromatin accessibility and profibrotic gene regulation. By integrating chromatin accessibility profiles (ATAC sequencing) we provide insight into the transcription network and open chromatin landscape underlying the switch in profibrotic myofibroblast states, emphasizing mechanoadaptive pathways linked to PAK1 as key drivers. Through genetic manipulation in liver and lung fibrosis, uncoupling PAK1-dependant signaling impaired the mechanoadaptive response in vitro and dramatically improved fibrosis in vivo. Moreover, we provide human validation for mechanisms underpinning PAK1 mediated mechanotransduction in liver and lung fibrosis. Collectively, these observations provide new insight into the nuclear mechanics driving the profibrotic chromatin landscape in fibrosis, highlighting actomyosin-dependent mechanisms linked to chromatin organisation as urgently needed therapeutic targets in fibrosis.