TGF-beta1 slows the growth of pathogenic myofibroblasts through a mechanism requiring the focal adhesion protein, Hic-5

Pathogenic scarring is a devastating disorder that impairs normal tissue function after injury. Differentiated myofibroblasts deposit and organize scars over a continuum, from normal to pathogenic, and yet the mechanisms regulating their appearance and disappearance from tissues are enigmatic. We reported previously that key functions of myofibroblasts derived from hypertrophic scars (HTSF) are constitutively activated by an autocrine loop involving transforming growth factor-beta1 (TGF-beta1). We now report that this autocrine induction of TGF-beta1 results in a constitutively high level of Hic-5, which markedly reduces HTSF proliferation relative to normal adult human dermal fibroblasts (NADF) without changing apoptosis. Cyclin D1 and A levels are constitutively lower in HTSF compared to NADF, and the cyclin-dependent kinase inhibitor p21(cip1) is upregulated in HTSF and located in the nucleus. Inhibition of autocrine TGF-beta1 production in HTSF reverses this process, lowering Hic-5 and p21(cip1) levels and increasing replication. Moreover, Hic-5 is partially localized in the nucleus of HTSF, and knocking down Hic-5 with specific siRNAs in these cells results in decreased p21(cip1) levels and a concomitant increase in proliferation. Our findings show that autocrine production of TGF-beta1 upregulates the expression of Hic-5, which is essential for perpetuating the decreased proliferation seen in this pathogenic myofibroblast

Hic-5 promotes the hypertrophic scar myofibroblast phenotype by regulating the TGF-beta1 autocrine loop

Following severe traumatic or thermal injury to the dermis, hypertrophic scars (HTSs) often develop in humans. These scar fibroblasts (hypertrophic scar fibroblasts (HTSFs)) retain the myofibroblast phenotype persistently, rather than transiently as in acute wounds. These pathogenic myofibroblasts constitutively express smooth-muscle cell alpha-actin (SMAA), deposit an excessive amount of extracellular matrix (ECM) proteins, are highly contractile, and stably display large focal adhesions. Increasing evidence supports a mechanism in which autocrine production and activation of transforming growth factor-beta1 (TGF-beta1) are required to maintain the pathogenic myofibroblast phenotype. We recently reported that Hic-5, a focal adhesion protein that is upregulated by TGF-beta1, is expressed persistently in HTSF compared to normal adult fibroblasts (NADFs). We now find that Hic-5 is an important regulator of the constitutive myofibroblast phenotype in HTSFs. Silencing the expression of Hic-5 in HTSFs with specific siRNAs dramatically reduces TGF-beta1 production, decreases the generation of supermature focal adhesions reduces expression of SMAA and decreases collagen contraction and ECM synthesis. Our findings demonstrate that Hic-5 is an essential component of the mechanism regulating autocrine production of TGF-beta1 and the resulting pathogenic myofibroblast phenotyp