Cdkn1a is a key mediator of rat pancreatic stellate cell senescence

Completion of pancreatic wound healing requires termination of pancreatic stellate cell (PSC) activation to prevent fibrosis. Besides induction of apoptosis and return to a quiescent phenotype, senescence of PSC followed by immune cell-mediated cytolysis represents a potential mechanism. Here, we have studied if the cell cycle inhibitor cyclin-dependent kinase inhibitor 1A (Cdkn1a, p21/Waf1), expression of which is increased in senescent rat PSC, plays a causative role in the senescence process.

Senescence was induced by doxorubicin treatment. The functions of Cdkn1a were analyzed using two approaches, treatment of primary rat PSC with siRNA and tetracycline-regulated overexpression of Cdkn1a in immortalized rat cells. Expression of senescence-associated β-galactosidase (SA β-Gal) was used as a surrogate marker of senescence.

The knockdown of Cdkn1a significantly attenuated the growth-inhibitory effect of doxorubicin and strongly diminished the portion of SA β-Gal-positive cells. Overexpression of Cdkn1a enhanced both the antiproliferative effect of doxorubicin and induction of senescence. In primary PSC, doxorubicin treatment was associated with increased expression of interleukin-6 (IL-6) and matrix metalloproteinase (MMP)-9, while expression of the activation marker α-smooth muscle actin (α-SMA), p53, Cdk1 and Rad54 was diminished. The application of Cdkn1a siRNA specifically antagonized the effects of doxorubicin on the expression of p53, Cdk1 and Rad54 but not IL-6 and α-SMA, while MMP-9 expression and also activity were even enhanced.

Cdkn1a plays a direct role in the process of rat PSC senescence. Additional Cdkn1a-independent pathways may contribute to the partial maintenance of a gene expression profile typical of senescent PSC.