Senescence determines the fate of activated rat pancreatic stellate cells

Abstract

In chronic pancreatitis (CP), persistent activation of pancreatic stellate cells (PSC) converts wound healing into a pathological process resulting in organ fibrosis. Here, we have analysed senescence as a novel mechanism involved in the termination of PSC activation and tissue repair. PSC senescence was first studied in vitro by establishing long-term cultures and by applying chemical triggers, using senescence-associated β-Galactosidase (SA β-Gal) as a surrogate marker. Subsequently, susceptibility of PSC to immune cell-mediated cytolysis was investigated employing cocultures. Using the model of dibutyltin dichloride-induced CP in rats, appearance of senescent cells was monitored by immunohistochemistry and immunofluorescence, and correlated with the progression of tissue damage and repair, immune cell infiltration and fibrosis. The results indicated that long-term culture and exposure of PSC to stressors (doxorubicin, H2O2 and staurosporine) induced senescence. Senescent PSC highly expressed CDKN1A/p21, mdm2 and interleukin (IL)-6, but displayed low levels of α-smooth muscle actin. Senescence increased the susceptibility of PSC to cytolysis. In CP, the number of senescent cells correlated with the severity of inflammation and the extension of fibrosis. Areas staining positive for SA β-Gal overlapped with regions of fibrosis and dense infiltrates of immune cells. Furthermore, a close physical proximity of immune cells and activated PSC was observed. We conclude that inflammation, PSC activation and cellular senescence are timely coupled processes which take place in the same microenvironment of the inflamed pancreas. Lymphocytes may play a dual-specific role in pancreatic fibrogenesis, triggering both the initiation of wound healing by activating PSC, and its completion by killing senescent stellate cells.

Physiological and clinically attainable concentrations of 1,25-dihydroxyvitamin D3 suppress proliferation and extracellular matrix protein expression in mouse pancreatic stellate cells

“…Senescence is a regular phenomenon in growth-arrested cells in vitro wherefore its significance as a potential response to 1,25(OH) 2 D 3 in PSCs in vivo needs further investigation. Interestingly, however, the development of cellular senescence followed by elimination of senescent PSCs by the immune system has previously been suggested as a plausible mechanism to limit fibrosis in the pancreas [32] and the liver [33].…”

Senescent cells: Living or dying is a matter of NK cells

“…Regarding pancreatitis, senescence of pancreatic stellate cells has been found to increase their susceptibility to immune cell cytotoxicity, including NK cell activity. Nevertheless, NK cell contribution to the pancreatic wound healing seems not essential, as fibrosis is not affected by NK cell depletion …”

The Role of Cellular Senescence in the Gastrointestinal Mucosa

“…The SA secretory phenotype results in a robust inflammatory cascade that leads to marked recruitment of immune cells 28. Fitzner et al41 hypothesized that senescence plays an integral role in the severity of inflammation and fibrosis seen in chronic pancreatitis. Using a model of dibutyltin dichloride-induced chronic pancreatitis in rats, cellular senescence was closely correlated with activation of pancreatic stellate cells as well as the severity of inflammation and extent of fibrosis.…”