Calcium chloride supplementation promotes longevity in <i>Caenorhabditis elegans</i> via a CKK-1 and CMK-1–dependent UNC-43/DAF-16 signaling mechanism

Calcium chloride can be used as a food additive and in medicine. The intake of calcium chloride can elevate the intracellular Ca2+ level, which subsequently activates the downstream proteins in the Ca2+/calmodulin-dependent protein kinase (CaMK) family. Based on evidence from the literature, we hypothesized that the calcium chloride supplementation may promote longevity by increasing intracellular Ca2+ levels, thereby activating the UNC-43/DAF-16 pathway, with potential involvement of the CKK-1 and CMK-1. The lifespan assays, health indexes (pharyngeal pumping and body bends), calcium imaging to assess the Ca2+ level, loss-of-function assays for the mutants, DAF-16 nuclear localization, UNC-43 protein localization, and Caenorhabditis elegans RNA interference (RNAi) experiments were conducted. The results showed that the supplementation of calcium chloride significantly extended the lifespan in a dose-dependent manner. At the most effective dose (2000 nmol/plate), calcium chloride increased the mean lifespan by 15.4%, enhanced the calcium-level fluorescence by 2.8 folds, and improved both the health indices. The longevity effects induced by the calcium chloride required the CKK-1, CMK-1, UNC-43, and DAF-16 proteins. Moreover, both the DAF-16 nuclear translocation and the longevity effects were significantly suppressed by the RNAi targeting the CKK-1, CMK-1 and UNC-43. Importantly, the maintenance of the UNC-43 in the cytoplasm was dependent on the CKK-1 and CMK-1, as demonstrated by the RNAi analyses. All of these results indicated that the calcium chloride supplementation can exert the longevity effects in the C. elegans via a CKK-1 and CMK-1-dependent UNC-43/DAF-16 signaling mechanism.