The PERK-GADD45A axis is a key driver of hepatic stellate cell activation

Hepatic stellate cells (HSCs) play a pivotal role in driving fibrosis during chronic liver injury. HSCs produce vast amounts of fibrotic proteins, causing endoplasmic reticulum (ER) stress and initiating the unfolded protein response (UPR). While the UPR is important for fibrogenesis, how signaling through UPR transducer Protein Kinase R-like ER Kinase (PERK) and its effectors impact HSC activation and fibrogenesis is unclear. Here, we sought to uncover the role of PERK and its effector GADD45A in liver fibrosis.

PERK-GADD45A signaling was assessed in primary and immortalized HSCs treated with TGFβ, and mouse models of fibrosis. Genetic and pharmacological disruption of PERK or GADD45A was used to assess the role of PERK or GADD45A in HSC activation, proliferation, and fibrogenesis. HSC-specific Gadd45a-null mice were utilized to investigate the role of GADD45A on CCl4-induced fibrosis.

We found that TGFβ-induction of collagen I drives activation of PERK signaling in HSCs. Furthermore, loss or inhibition of PERK limits long-term HSC activation as illustrated by reduced levels of collagen I and fibronectin, impaired collagen I deposition, and reduced cell proliferation in vitro. Next, we show that PERK signaling induces expression of GADD45A during HSC activation, and loss of GADD45A disrupts HSC activation and expression of proliferation and cell-cycle-associated genes in immortalized and primary HSCs. Finally, HSC-specific GADD4Aa loss limits CCl4-driven fibrogenesis in vivo.

PERK signaling is critical for HSC activation, and loss of the PERK downstream effector GADD45A limits fibrosis progression. Disruption of HSC activation and proliferation, coupled with dysregulation of cell-cycle-associated genes upon PERK or GADD45A loss, suggests that PERK-GADD45A signaling impacts multiple facets of HSC pathophysiology.