Aged liver is usually impaired in response to hepatic injury. Tissue-specific stem cells participate in the repair of tissue injury. However, how oval cells (OCs) respond to injury and how the process is regulated by tissue microenvironment in aged mice have not been fully understood. In this study, taking advantage of well-established murine OC activation model, we demonstrated that OCs were less activated upon injury in aged mice and the impairment was mainly attributed to dysfunction in their niche. Through analyzing global gene expression, we found that the genes differentially expressed in damaged young and aged mouse liver tissues were predominantly those required for the formation and remodeling of extracellular matrix. As one of the most important extracellular matrix components in the OC niche, laminin was shown to promote the proliferation of OCs. Not surprisingly, laminin was downregulated with aging. Consistent with the downregulation of genes encoding DNA-dependent protein kinase (DNA-PK) proteins in aged hepatic stellate cells (HSCs), inhibition of DNA-PK also led to reduced expression of laminin in HSCs. Moreover, impairment in OC activation caused by less supporting from DNA-damaged HSCs could be rescued by laminin. This study reveals a new cellular mechanism underlying impaired OCs functionality during aging.
Keywords: DNA-dependent protein kinase; aging; hepatic stellate cells; niche; oval cells.