STUDY OF MICE IN WHICH THE TGF-BETA1 GENE HAS BEEN DISRUPTED

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Of the three isoforms of TGF-beta, TGF-beta1 is both the most abundant and the most acutely regulated in injury, repair, and disease pathogenesis. Although they lack any obvious developmental defects, mice in which the TGF-beta1 gene has been knocked out by targeted disruption die at about 3 weeks of age of multifocal inflammatory disease and autoimmune symptomatology. We have used wound healing to identify specific cellular functions and cell-cell interactions which are altered by the loss of TGF-beta1. In contrast to predictions based on the vulnerary effects of exogenous TGF-beta1, lack of the endogenous protein improves healing of cutaneous wounds, enhancing the rate of re- epithelialization, reducing the amount of granulation tissue, and improving connective tissue remodeling. We are also collaborating with Chuxia Deng (NIDDK) to study wound healing in mice null or heterozygous for Smads 2 and 3, cytoplasmic intermediates in TGF-beta signaling pathways. These studies are permitting identification of specific pathways involved in wound healing and show that Smad3 and not Smad2 mediates suppressive effects of TGF-beta on re-epithelialization.Other studies in TGF-beta1 null mice have shown suppressed expression of the mRNAs for several mitochondrially encoded components of the electron- transport chain, consistent with observations of ultrastructural abnormalities in Golgi and mitochondria of cells of liver, heart, and lung of TGF-beta1 null mice suggestive of an energy deficit and impaired vesicular transport. This is particularly intriguing in light of previous findings from this laboratory of localization of intracellular TGF-beta1 to mitochondria. Functional studies have shown that whereas maximal capacity of individual electron chain components is not altered in the null mice, there is a significant decrease in the oxidative capacity of heart tissue. Moreover, studies with hepatocyte cell lines derived from these mice show that null cells have reduced oxygen consumption compared to wildtype cells. Treatment of either null or wildtype cells with TGF-beta in vitro results in rapid upregulation of expression of mitochondrial genes and restores, in part, the deficit in oxidative metabolism. Present investigations are aimed at determining the mechanism whereby TGF-beta1 regulates cellular energetics and expression of mitochondrial genes. - cell energetics, growth factors, Inflammation, mitochondria, TGF-beta,