Transforming growth factor beta responsiveness is modulated by the extracellular collagen matrix during hepatic ito...

Hepatic sinusoidal Ito cells have the capacity to produce interstitial collagen types I and III as well as other matrix proteins and may be involved in hepatic fibrogenesis. Transforming growth factor beta (TGF beta) responsiveness was evaluated during in vitro cell culture, since increasing evidence suggests that this ubiquitous polypeptide can stimulate the production of collagenous proteins in a variety of cell types. TGF beta induced marked inhibition of Ito cell proliferation for cells grown on either a type I or a type IV collagen matrix. In marked contrast, the collagen synthetic response was considerably different for cells grown on a type I versus a type IV collagen matrix. When cells were grown on a type I collagen matrix, TGF beta caused a significant increase in the accumulation of collagen type I and III. When Ito cells were grown on a type IV collagen matrix, there was no stimulation of collagen production. TGF beta responsiveness was also evaluated in the setting of altered vitamin A concentrations. Freshly isolated Ito cells are engorged with vitamin A, the usual physiologic storage site for hepatic vitamin A. During in vitro culture and during in vivo fibrogenesis, Ito cells lose their vitamin A stores coincident with a transformation to a collagen-producing myofibroblast-like cell. When cultured Ito cells were grown on a type I collagen matrix and re-exposed to an increased concentration of vitamin A, the production of interstitial collagen was reduced. However, when the vitamin A-enriched Ito cells were exposed to TGF beta, the production of interstitial collagen was increased, similar to cells that had not received vitamin A.