The Liver in Transforming Growth Factor-Beta-1 (TGF-β1) Null Mutant Mice

Abstract

Transforming growth factor-beta-1 (TGF-beta 1) null mutant mice have no gross developmental abnormalities at birth but succumb to multifocal inflammatory lesions that lead to organ failure and death about 20 days after birth. Treatment with anti-inflammatory and immune suppressive agents, such as rapamycin, reduces the severity and extent of inflammatory infiltrates in the liver and can prolong the life of knockout (KO) mice compared to untreated null mice. To determine whether there is an associated hepatic phenotype, livers of "young" (< 3 weeks), "old" (> 3 weeks), and age-matched wild-type (WT) mice were studied using light and electronmicroscopy. On light microscopy, old KO mice had foci of mononuclear cells in liver parenchyma in addition to scattered foci of megalocytosis. Intracytoplasmic vacuoles, some of which were juxtanuclear in location, were also seen but these were most prominent in the oldest (10 weeks) rapamycin-treated mouse. In the untreated young KO mice, there were only foci of mononuclear cells in the liver parenchyma and portal tracts and variable numbers of binucleated hepatocytes. Ultrastructurally, there was a significant increase in the number of mitochondria in livers of the old KO mice, when compared either to the age-matched wild-type or to the young KO mice (p > .001). Hepatocytes from all KO mice showed increased numbers of hypertrophied or enlarged Golgi complexes compared to age-matched wild-type mice. Intracytoplasmic canaliculi lined with microvilli were seen in livers of old KO mice, but were absent in the young KO and wild-type mice. Primary cultures of hepatocytes, derived from livers of both young and old KO mice, showed similar changes on phase contrast and electronmicroscopy. These included juxtanuclear vacuoles, intracytoplasmic canaliculi, enlarged Golgi vesicles, and increased numbers of autolysosomes. Phenotypic abnormalities of mitochondria were either minimal or absent in cultured KO hepatocytes. The findings demonstrate, for the first time, that targeted disruption of the TGF-beta 1 gene in mice results in an altered ultrastructural phenotype of hepatocytes. The data suggest that TGF-beta 1 may be required for normal development and regulation of subcellular organelles in hepatocytes and may be essential for physiological functions involving mitochondria and Golgi complex.

Genetic Regulation of Autoimmune Disease: BALB/c Background TGF-β1-Deficient Mice Develop Necroinflammatory IFN-γ-Dependent Hepatitis

“…Previous reports of TGF-␤1 Ϫ/Ϫ mice described extensive inflammatory heart and lung disease, with cardiac and pulmonary inflammation observed in 95 to 100% of mice (19,20). By contrast, reports indicated liver involvement in only ϳ70% of mice, which, when present, is not accompanied by hepatic lesions at the grossly observable level (18) and is typically associated with only modest histopathological changes, consisting of moderate periportal inflammation, but preservation of hepatic architecture (i.e., no hepatocyte loss (19,20)). Our findings in 129/CF-1-TGF-␤1 Ϫ/Ϫ mice (no gross hepatic lesions, periportal inflammation without extensive hepatocyte necrosis, and normal plasma ALT levels in 9 of 10 mice) are completely consistent with these previously published findings.…”

“…Death of TGF-␤1 Ϫ/Ϫ mice is believed to be due to cardiopulmonary failure (17). A proportion of TGF-␤1 Ϫ/Ϫ mice demonstrates mild liver inflammation, which typically does not cause hepatocyte loss or compromise liver function (18). Inflammatory lesions in TGF-␤1 Ϫ/Ϫ mice are heterogeneously distributed, with considerable mouse to mouse variability (19,20).…”

Medical Applications of Transforming Growth Factor-

“…In addition to immune system defects, the mice that are born experience delayed wound healing, 55 ineffective remodeling of bone, 56 and increased mitochondria in the liver in response to stress. 57 TGF-β2 knockout mice exhibit primarily developmental defects in contrast to TGF-β1 mice. 58 These include defects in epithelial-mesenchymal interactions, cell growth, extracellular matrix production and tissue remodeling, and affect the function of cardiac, lung, craniofacial, limb, spinal column, eye, inner ear and urogenital tissues.…”

The mitochondrial component of intracrine action

“…Depending on the conditions, TGF-␤ increases ROS generation and thereby induces senescence (76). At the same time, it can be noted that the hepatocytes of TGF-␤ knockout mice demonstrate an increased number of phenotypically nor-mal mitochondria (74). This suggests that one function of TGF-␤ is to regulate the removal of mitochondria damaged in part secondary to the cytokine's stimulation of ROS.…”

“…TGF-␤ are important fibrogenic cytokines with important roles in apoptosis and senescence (5,24,64,68,69,74,76). Liver stellate and Kupffer cells contain the large latent TGF-␤ complex consisting of the mature TGF-␤ protein linked noncovalently to the NH 2 -terminal portion of the precursor protein, latency-associated peptide.…”