Hepatic stellate cell plasticity and maladaptive fibrogenic memory in chronic liver disease - PROJECT SUMMARY Hepatic stellate cell plasticity and maladaptive fibrogenic memory in chronic liver disease Fibrosis associated with chronic liver disease affects hundreds of millions of patients worldwide. Hepatic stellate cells (HSCs), in turn, represent the main cellular driver of hepatic fibrosis. A key unanswered question is why HSCs activate to facilitate tissue repair in response to acute liver injury but hyperactivate to produce exuberant extracellular matrix in response to repeated liver injury, leading to fibrosis. Central to this behavior switch is a mechanism for HSCs to remember previous injury episodes in order to respond differently, i.e. hyperactivate, when exposed to re-injury. Recent studies, including ours (Wang et al. Dev Cell 2019), strongly support the epigenome and in particular DNA methylation patterns as the carrier of cell memory in development and in tissue injury. The objective of this research is to clarify how the epigenome and specifically DNA methylation patterns encode this maladaptive cell memory and amplify HSC’s fibrogenic response following re-injury. This proposal builds upon recent advances in single cell technology and low-input chromatin profiling which we optimized extensively to measure HSC gene expression and epigenomic changes in vivo in a novel mouse model of fibrogenic memory. In our fibrogenic memory model, HSCs completely deactivate following fibrosis regression, with their transcriptome indistinguishable from uninjured HSCs, however epigenomic changes persist in the form of chromatin accessibility changes. In response to re-injury, HSCs from regressed liver hyperactivate and are driven by unique transcriptional networks (WT1, TEAD1, TBX20, and PBX1) not found in HSCs undergoing initial injury. Using the Uhrf1 floxed mice generated previously in our Dev Cell paper to specifically remove Uhrf1, a critical component of the DNA methylation machinery, in HSCs, we found that these mice display augmented fibrogenic memory in response to re-injury. Our central hypothesis is that memory of previous injury through epigenetic changes modify HSC plasticity and amplify their activation in response to re-injury. We will address this hypothesis in three interrelated, but distinct specific aims:1) Define the regulatory elements controlling fibrogenic memory in HSCs; 2) Determine how UHRF1 and the DNA methylome control fibrogenic memory in HSCs; 3) Uncover novel regulatory nodes driving HSC’s maladaptive response in re-injury. This innovative approach leveraging cutting-edge genomics technology and unique animal models is significant because it will yield fundamental new insights into stellate cell biology by uncovering the epigenetic basis of fibrogenic memory, the contribution of specific genes and transcriptional networks to fibrogenic memory and hepatic fibrosis, and conserved fibrogenic drivers in liver disease patients that can lead to potential therapeutic targets.
