Purpose: To determine whether protein kinase a (PKA) and exchange protein for cAMP 1 (Epac1) inhibit NIMA-related kinase 7 (Nek7) to block the NOD-like receptor family pyrin domain-containing family member 3 (NLRP3) signaling pathway.
Methods: Retinal endothelial cells (RECs) were grown in normal (5 mM) or high (25 mM) glucose. Some cells were treated with a Nek7 cDNA plasmid, Nek7 siRNA; an Epac1 agonist, forskolin; a PKA agonist; or an empty vector. Epac1 floxed and Cdh5-cre Epac1 mice and Nek7 floxed and Cdh5-cre Nek7 mice were also used. Western blot analyses were done on cell culture or whole retinal lysates for NLRP3, cleaved caspase 1, interleukin-1-beta (IL-1β). A PKA activity assay was also done.
Results: Nek7 cDNA increased NLRP3 signaling proteins, but Nek7 siRNA inhibited high-glucose induction of these proteins in retinal endothelial cells. Epac1 and forskolin both reduced Nek7 and NLRP3 pathway proteins, even when given in combination with Nek7 cDNA. Elimination of Nek7 in endothelial cells reduced NLRP3 signaling proteins in whole retinal lysates from mice.
Conclusions: Nek7 regulated NLRP3 inflammasome protein levels both in vitro and in vivo. Both Epac1 and PKA lie upstream of Nek7 and NLRP3 and can overcome excessive Nek7 levels. These studies establish that cAMP proteins can inhibit Nek7 and block activation of the NLRP3 inflammasome proteins.