Bone marrow stem cells develop into hematopoietic and mesenchymal lineages but have not been known to participate in production of hepatocytes, biliary cells, or oval cells during liver regeneration. Cross-sex or cross-strain bone marrow and whole liver transplantation were used to trace the origin of the repopulating liver cells. Transplanted rats were treated with 2-acetylaminofluorene, to block hepatocyte proliferation, and then hepatic injury, to induce oval cell proliferation. Markers for Y chromosome, dipeptidyl peptidase IV enzyme, and L21-6 antigen were used to identify liver cells of bone marrow origin. From these cells, a proportion of the regenerated hepatic cells were shown to be donor-derived. Thus, a stem cell associated with the bone marrow has epithelial cell lineage capability.

Cortical interneurons arise from the proliferative zone of the ventral telencephalon, the ganglionic eminence, and migrate into the developing neocortex. The spatial patterns of migratory interneurons reflect the complementary expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, MET, in the forebrain. Scatter assays on forebrain explants demonstrate regionally specific motogenic activity due to HGF/SF. In addition, exogenous ligand disrupts normal cell migration. Mice lacking the urokinase-type plasminogen activator receptor (u-PAR), a key component of HGF/SF activation, exhibit deficient scatter activity in the forebrain, abnormal interneuron migration from the ganglionic eminence, and reduced interneurons in the frontal and parietal cortex. The data suggest that HGF/SF motogenic activity, which is essential for normal development of other organ systems, is a conserved mechanism that regulates trans-telencephalic migration of interneurons.

Tissue-type plasminogen activator (tPA), a serine protease well known for generating plasmin, has been demonstrated to induce matrix metalloproteinase-9 (MMP-9) gene expression and protein secretion in renal interstitial fibroblasts. However, exactly how tPA transduces its signal into the nucleus to control gene expression is unknown. This study investigated the mechanism by which tPA induces MMP-9 gene expression. Both wild-type and non-enzymatic mutant tPA were found to induce MMP-9 expression in rat kidney interstitial fibroblasts (NRK-49F), indicating that the actions of tPA are independent of its proteolytic activity. tPA bound to the low density lipoprotein receptor-related protein-1 (LRP-1) in NRK-49F cells, and this binding was competitively abrogated by the LRP-1 antagonist, the receptor-associated protein. In mouse embryonic fibroblasts (PEA-13) lacking LRP-1, tPA failed to induce MMP-9 expression. Furthermore, tPA induced rapid tyrosine phosphorylation on the ␤ subunit of LRP-1, which was followed by the activation of Mek1 and its downstream Erk-1 and -2. Blockade of Erk-1/2 activation by the Mek1 inhibitor abolished MMP-9 induction by tPA in NRK-49F cells. Conversely, overexpression of constitutively activated Mek1 induced Erk-1/2 phosphorylation and MMP-9 expression. In mouse obstructed kidney, tPA, LRP-1, and MMP-9 were concomitantly induced in the renal interstitium. Collectively, these results suggest that besides its classical proteolytic activity, tPA acts as a cytokine that binds to the cell membrane receptor LRP-1, induces its tyrosine phosphorylation, and triggers intracellular signal transduction, thereby inducing specific gene expression in renal interstitial fibroblasts. Tissue-type plasminogen activator (tPA)2 is a serine protease that plays a pivotal role in blood coagulation and fibrinolysis. In the kidney, the main function of tPA is to convert plasminogen into the biologically active plasmin, which in turn participates in regulating the catabolism of extracellular matrix and tissue fibrosis (1). In light of its proteolytic potential, tPA has generally been considered to be beneficial in the pathogenesis of fibrotic lesions, leading to increased matrix degradation and decreased matrix accumulation (2). However, previous studies from our laboratory demonstrate that genetic ablation of tPA actually protects the kidney from development of interstitial fibrosis in obstructive nephropathy (3), suggesting that increased tPA is detrimental in certain pathological situations. The deleterious effect of tPA is attributed to its ability to induce matrix metalloproteinase-9 (MMP-9) production, which leads to the destruction of the tubular basement membrane and subsequent generation of the matrix-producing myofibroblasts via tubular epithelial to mesenchymal transition (4, 5). In vitro, tPA directly induces MMP-9 gene expression and protein secretion in renal interstitial fibroblast cells (3). However, how tPA, a well known serine protease, transduces its signal into the nucleus to control specifi...

Tissue-type plasminogen activator (tPA) is one of the major components in the matrix proteolytic network whose role in the pathogenesis of renal interstitial fibrosis remains largely unknown. Here, we demonstrate that ablation of tPA attenuated renal interstitial fibrotic lesions in obstructive nephropathy. Mice lacking tPA developed less morphological injury and displayed a reduced deposition of interstitial collagen III and fibronectin as well as total tissue collagen in the kidneys after sustained ureteral obstruction, when compared with their wild-type counterparts. Deficiency of tPA selectively blocked tubular epithelial-to-myofibroblast transition (EMT), but did not affect myofibroblastic activation from interstitial fibroblasts. A marked decrease in matrix metalloproteinase-9 (MMP-9) induction was found in the obstructed kidneys of tPA -/-mice, which led to a dramatic preservation of the structural and functional integrity of tubular basement membrane (TBM). In vitro, tPA induced MMP-9 gene expression and protein secretion in renal interstitial fibroblasts. Thus, increased tPA is detrimental in renal interstitial fibrogenesis through a cascade of events that lead to MMP-9 induction, TBM destruction, and promotion of EMT. Our findings establish a crucial and definite importance of EMT in the pathogenesis of renal interstitial fibrosis at the whole-animal level.

The activation of interstitial fibroblasts to become alpha-SMA-positive myofibroblasts is an essential step in the evolution of chronic kidney fibrosis, as myofibroblasts are responsible for the production and deposition of the ECM components that are a hallmark of the disease. Here we describe a signaling pathway that leads to this activation. Tissue-type plasminogen activator (tPA) promoted TGF-beta1-mediated alpha-SMA and type I collagen expression in rat kidney interstitial fibroblasts. This fibrogenic effect was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). In rat kidney fibroblasts, tPA induced rapid LRP-1 tyrosine phosphorylation and enhanced beta1 integrin recruitment by facilitating the LRP-1/beta1 integrin complex formation. Blockade or knockdown of beta1 integrin abolished type I collagen and alpha-SMA expression. Furthermore, inhibition of the integrin-linked kinase (ILK), a downstream effector of beta1 integrin, or disruption of beta1 integrin/ILK engagement, abrogated the tPA action, whereas ectopic expression of ILK mimicked tPA in promoting myofibroblast activation. In murine renal interstitium after obstructive injury, tPA and alpha-SMA colocalized with LRP-1, and tPA deficiency reduced LRP-1/beta1 integrin interaction and myofibroblast activation. These findings show that tPA induces LRP-1 tyrosine phosphorylation, which in turn facilitates the LRP-1-mediated recruitment of beta1 integrin and downstream ILK signaling, thereby leading to myofibroblast activation. This study implicates tPA as a fibrogenic cytokine that promotes the progression of kidney fibrosis.