CSRP2, TIMP‐1, and SM22α promoter fragments direct hepatic stellate cell‐specific transgene expression in vitro, but not in vivo

Abstract

The activation of hepatic stellate cells (HSC) and their transdifferentiation into myofibroblasts (MFB) is the key step for development of liver fibrosis. Over the past several years, significant progress has been made in the understanding of the critical pathways involved incells undergoing activation. Cellular activation in the course of transdifferentiation involves, among other biochemical modifications, functionally relevant changes in the control of gene expression. These include the up-regulation of transcription factors, different extracellular matrix proteins, cell adhesion molecules, smooth muscle specific genes, and proteins involved in matrix remodelling, or cytoskeletal organization. The corresponding regulatory elements of these genes have afforded us the opportunity to express transgenes with antifibrotic potential in a cell type- and/or transdifferentiation-dependent manner. In the present study, we have tested several promoters for their ability to mediate cell-specific expression, including those for CSRP2, SM22alpha, and TIMP-1 (CSRP2, gene encoding the LIM domain protein CRP2; SM22alpha, smooth muscle-specific gene encoding a 22-kDa protein; TIMP-1, gene encoding the tissue inhibitor of metalloproteinases-1), which in liver are specifically expressed in HSC or become strongly activated during the acute remodelling into MFB. We constructed adenoviral reporter vectors in which relevant portions of the promoters were fused to the green fluorescent protein. Our experiments demonstrate that each of these promoters is sufficient to achieve strong or partially selective expression in vitro but none is able to direct a specific or inducible expression of transgenes in HSC/MFB in vivo.