Overwhelming high quantities of the matricellular protein CCN1/CYR61 induce ER stress-related cellular apoptosis in hepatic stellate cells

Background: CCN1/CYR61 is a matricellular protein belonging to CCN protein family that contains six secreted proteins associated with extracellular matrix signaling [1]. It acts as an enhancer of cutaneous wound healing process by preventing hypertrophic scar formation through induction of myofibroblast (MFB) senescence [2]. In liver fibrosis, senescent cells are primarily derived from activated hepatic stellate cells (HSC) that initially proliferate in response to liver damage and transdifferentiate into MFB. Activated HSC and transdifferentiated MFB are one major source of CCN1 [3]. Methods: We tested if CCN1 act as a senescence inducer to attenuate liver fibrogenesis by means of adenoviral CCN1 gene transfer in primary HSC, MFB, CFSC-2G, and LX-2. Results: The overwhelming concentrations of CCN1 protein resulted in an overload of the endoplasmic reticulum (ER) and compensatory unfolded protein response (UPR) in all these cells. The UPR resulted in upregulation of ER chaperones (BIP/Grp78, Grp94) and leads to an activation of IRE1α as evidenced by spliced XBP1 mRNA with IRE1α-induced JNK phosphorylation. The UPR arm PERK and eIF2a was phosphorylated, and CHOP upregulated. Ad5-CMV-CCN1 induced HSC apoptosis by proteolytic cleavage of caspase-12, caspase-9, and caspase-3 resulting in positive TUNEL stain. Remarkably, CCN1 effectively blocked collagen type I expression at both mRNA and protein levels. Conclusions: High concentrations of the matricellular protein CCN1 induce HSC apoptosis through ER stress and UPR. Therapeutic CCN1 gene transfer might be useful to mitigate liver fibrosis when cell-specific targeted to HSC and MFB.