RESUMO
To date the molecular signals regulating activation, proliferation, and differentiation of hepatic oval cells are not fully understood. The Wnt family is essential in hepatic embryogenesis and implicated in hepatic carcinogenesis. This study elucidates novel findings implicating Wnt1 in directing oval cell differentiation during the rat 2-acetylaminofluorene (2AAF) and 2/3 partial hepatectomy (PHx) liver regeneration model. Proteins of Wnt family members were predominantly localized in pericentral hepatocytes during liver injury, oval cell activation, and hepatocyte regeneration. In addition, Wnt message increased coinciding with the rise in oval cell number, whereas protein levels peaked immediately after the height of oval cell proliferation. Immunohistochemical analysis demonstrated nuclear translocation of beta-catenin within oval cells throughout the 2AAF/PHx protocol. Furthermore, RNA interference was used in vivo to confirm the physiological requirement of Wnt1 during the oval cell induction. Ultimately, inhibition of Wnt1 resulted in failure of oval cells to differentiate into hepatocytes and alternatively induced atypical ductular hyperplasia. Taken together, these data indicate that in vivo exposure to Wnt1 shRNA inhibited rat oval cell liver regeneration. In the absence of Wnt1 signaling, oval cells failed to differentiate into hepatocytes and underwent atypical ductular hyperplasia, exhibiting epithelial metaplasia and mucin production. Furthermore, changes in Wnt1 levels are required for the efficient regeneration of the liver by oval cells during massive hepatic injury.
Assuntos
Diferenciação Celular/fisiologia , Regeneração Hepática/fisiologia , Fígado/citologia , Células-Tronco/fisiologia , Proteína Wnt1/metabolismo , 2-Acetilaminofluoreno/farmacologia , Animais , Antígenos de Diferenciação/genética , Antígenos de Diferenciação/metabolismo , Carcinógenos/farmacologia , Receptores Frizzled/genética , Receptores Frizzled/metabolismo , Hepatectomia , Fígado/efeitos dos fármacos , Fígado/patologia , Fígado/cirurgia , Masculino , Tamanho do Órgão , Interferência de RNA , Ratos , Ratos Endogâmicos F344 , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Receptores de Neurotransmissores/genética , Receptores de Neurotransmissores/metabolismo , Transdução de Sinais/fisiologia , Células-Tronco/citologia , Proteína Wnt1/genética , alfa-Fetoproteínas/genética , alfa-Fetoproteínas/metabolismo , beta Catenina/genética , beta Catenina/metabolismoRESUMO
Hepatocyte growth factor (HGF) can induce proliferation and migration of intestinal epithelial cells and has also been shown to be important in wound healing of inflamed mucosal tissues. HGF is known to be expressed along with interleukin-1 (IL-1) by inflamed mucosal tissues, yet the effect of HGF on IL-1-induced proinflammatory cytokine responses by colonic epithelial cells is unknown. In this report, we have examined the effect of HGF on IL-1-induced secretion of IL-8 by the Caco-2 colonic epithelial cell line. HGF stimulation alone had no effect on the secretion of IL-8 by the Caco-2 cells. However, culture of the cells with HGF and suboptimal levels of IL-1 resulted in a significant enhancement of IL-8 secretion compared to cells cultured with IL-1 alone. A similar effect was seen with HGF and IL-1 simulation of monocyte chemoattractant protein-1 secretion by the rat IEC-6 intestinal epithelial cell line. The enhancing effect of HGF was seen regardless of whether the culture medium contained serum or not. Simultaneous stimulation with HGF and IL-1 was required for the enhancing effect as cells pretreated with HGF for 24 h and then stimulated with IL-1 alone secreted IL-8 levels similar to that of cells stimulated with IL-1 alone. These results suggest that in addition to wound healing, HGF may play a role in the IL-1-induced chemokine response of epithelial cells in inflamed mucosal tissues.