Characterisation of mice lacking the inflammatory caspases-1/11/12 reveals no contribution of caspase-12 to cell death and sepsis.

Caspases exert critical functions in diverse cell death pathways, including apoptosis and pyroptosis, but some caspases also have roles in the processing of cytokines into their functional forms during inflammation. The roles of many caspases have been unravelled by the generation of knockout mice, but still very little is known about the overlapping functions of caspases as only a few studies report on double or triple caspase knockout mice. For example, the functions of caspase-12 in cell death and inflammation, on its own or overlapping with the functions of caspase-1 and caspase-11, are only poorly understood. Therefore, we generated a novel mutant mouse strain lacking all three inflammatory caspases, caspases-1, -11 and -12. Analysis under steady state conditions showed no obvious differences between caspase-1/11/12-/- and wildtype (WT) mice. Since caspases-1 and -11 are involved in endotoxic shock, we analysed the response of caspase-1/11/12-/- mice to high-dose LPS injection. Interestingly, we could not detect any differences in responses between caspase-1/11/12-/- mice vs. caspase-1/11 double knockout mice. Furthermore, cell lines generated from caspase-1/11/12-/- mice showed no differences in their apoptotic or necroptotic responses to a diverse set of cytotoxic drugs in vitro when compared to WT cells. Importantly, these drugs also included ER stress-inducing agents, such as thapsigargin and tunicamycin, a form of cell death for which a critical pro-apoptotic function of caspase-12 has previously been reported. Additionally, we found no differences between caspase-1/11/12-/- and WT mice in their in vivo responses to the ER stress-inducing agent, tunicamycin. Collectively, these findings reveal that caspase-12 does not have readily recognisable overlapping roles with caspases-1 and -11 in the inflammatory response induced by LPS and in necroptosis and apoptosis induced by diverse cytotoxic agents, including the ones that elicit ER stress.