Abstract
The major cellular event in the development and progression of liver fibrosis is the activation of hepatic stellate cells (HSCs). Activated HSCs proliferate and produce excess collagen, leading to accumulation of scar matrix and fibrotic liver. As such, the induction of activated HSC death has been proposed as a means to achieve resolution of liver fibrosis. Here we demonstrate that cannabidiol (CBD), a major non-psychoactive component of the plant Cannabis sativa, induces apoptosis in activated HSCs through a cannabinoid receptor-independent mechanism. CBD elicits an endoplasmic reticulum (ER) stress response, characterized by changes in ER morphology and the initiation of RNA-dependent protein kinase-like ER kinase-, activating transcription factor-6-, and inositol-requiring ER-to-nucleus signal kinase-1 (IRE1)-mediated signaling cascades. Furthermore, CBD induces downstream activation of the pro-apoptotic IRE1/ASK1/c-Jun N-terminal kinase pathway, leading to HSC death. Importantly, we show that this mechanism of CBD-induced ER stress-mediated apoptosis is specific to activated HSCs, as it occurs in activated human and rat HSC lines, and in primary in vivo-activated mouse HSCs, but not in quiescent HSCs or primary hepatocytes from rat. Finally, we provide evidence that the elevated basal level of ER stress in activated HSCs has a role in their susceptibility to the pro-apoptotic effect of CBD. We propose that CBD, by selectively inducing death of activated HSCs, represents a potential therapeutic agent for the treatment of liver fibrosis.