RESUMO
BACKGROUND & AIMS: Knockout studies of the murine Nuclear Factor I-C (NFI-C) transcription factor revealed abnormal skin wound healing and growth of its appendages, suggesting a role in controlling cell proliferation in adult regenerative processes. Liver regeneration following partial hepatectomy (PH) is a well-established regenerative model whereby changes elicited in hepatocytes lead to their rapid and phased proliferation. Although NFI-C is highly expressed in the liver, no hepatic function was yet established for this transcription factor. This study aimed to determine whether NFI-C may play a role in hepatocyte proliferation and liver regeneration. METHODS: Liver regeneration and cell proliferation pathways following two-thirds PH were investigated in NFI-C knockout (ko) and wild-type (wt) mice. RESULTS: We show that the absence of NFI-C impaired hepatocyte proliferation because of plasminogen activator I (PAI-1) overexpression and the subsequent suppression of urokinase plasminogen activator (uPA) activity and hepatocyte growth factor (HGF) signalling, a potent hepatocyte mitogen. This indicated that NFI-C first acts to promote hepatocyte proliferation at the onset of liver regeneration in wt mice. The subsequent transient down regulation of NFI-C, as can be explained by a self-regulatory feedback loop with transforming growth factor beta 1 (TGF-ß1), may limit the number of hepatocytes entering the first wave of cell division and/or prevent late initiations of mitosis. CONCLUSION: NFI-C acts as a regulator of the phased hepatocyte proliferation during liver regeneration.
Assuntos
Proliferação de Células , Regeneração Hepática , Fígado/metabolismo , Fatores de Transcrição NFI/metabolismo , Animais , Retroalimentação Fisiológica , Regulação da Expressão Gênica , Genótipo , Hepatectomia/métodos , Fator de Crescimento de Hepatócito/genética , Fator de Crescimento de Hepatócito/metabolismo , Fígado/patologia , Fígado/fisiopatologia , Fígado/cirurgia , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fatores de Transcrição NFI/deficiência , Fatores de Transcrição NFI/genética , Fenótipo , Inibidor 1 de Ativador de Plasminogênio/genética , Inibidor 1 de Ativador de Plasminogênio/metabolismo , Transdução de Sinais , Fatores de Tempo , Fator de Crescimento Transformador beta1/genética , Fator de Crescimento Transformador beta1/metabolismo , Ativador de Plasminogênio Tipo Uroquinase/genética , Ativador de Plasminogênio Tipo Uroquinase/metabolismoRESUMO
Skin appendages such as teeth and hair share several common signaling pathways. The nuclear factor I C (NFI-C) transcription factor has been implicated in tooth development, but a potential role in hair growth had not been assessed. In this study we found that NFI-C regulates the onset of the hair growth cycle. NFI-C(-/-) mice were delayed in the transition from the telogen to anagen phase of the hair follicle cycle after either experimental depilation or spontaneous hair loss. Lack of NFI-C resulted in delayed induction of the sonic hedgehog, Wnt5a, and Lef1 gene expression, which are key regulators of the hair follicle growth initiation. NFI-C(-/-) mice also showed elevated levels of transforming growth factor ß1 (TGF-ß1), an inhibitor of keratinocyte proliferation, and of the cell cycle inhibitor p21 at telogen. Reduced expression of Ki67, a marker of cell proliferation, was noted at the onset of anagen, indicating impaired activation of the hair progenitor cells. These findings implicate NFI-C in the repression of TGF-ß1 signaling during telogen stage, resulting in the delay of progenitor cell proliferation and hair follicle regeneration in NFI-C-deficient mice. Taken together with prior observations, these findings also designate NFI-C as a regulator of adult progenitor cell proliferation and of postnatal tissue growth or regeneration.
