PKCδ-IRAK1 axis regulates oxidized LDL induced IL-1β prod uction in monocytes

Abstract

Present study examined the role of IL-1R-associated kinase (IRAK) and protein kinase C (PKC) in Oxidized LDL (Ox-LDL) induced monocyte IL-1β production. In THP1 cells Ox-LDL induced time dependent secretory IL-1β, IRAK1 activity, IRAK4, IRAK3, CD36 protein expression, PKCδ-JNK1 phosphorylation and AP1 activation. IRAK1/4 siRNA and inhibitor attenuated Ox-LDL induced secreted IL-1β and pro-IL-1β mRNA, pro and mature IL-1β protein expression respectively. DPI (NADPH oxidase inhibitor) and NAC (Free radical scavenger) attenuated Ox-LDL induced reactive oxygen species (ROS) generation, caspase 1 activity and pro and mature IL-1β expression. Ox-LDL induced secretory IL-1β production was abrogated in presence of JNK Inhibitor II, Tanshinone IIa, Ro-31-8220, Go6976, Rottlerin and PKCδ siRNA. PKCδ siRNA, attenuated Ox-LDL induced increase in IRAK1 kinase activity, JNK1 phosphorylation and AP1 activation. In THP-1 macrophages, CD36, TLR2, 4, 6 and PKCδ SiRNA prevented Ox-LDL induced PKCδ, IRAK1 activation and IL-1β production. Enhanced Ox-LDL and IL-1β in SIRS patient plasma demonstrated positive correlation among each other and with disease severity scores. Ox-LDL containing plasma induced PKCδ, IRAK1 phosphorylation and IL-1β production in CD36, TLR 2,4 and 6 dependent manner in primary human monocytes. Results suggest involvement of CD36, TLR2,4,6 and PKCδ-IRAK1-JNK1-AP-1 axis in Ox-LDL induced IL-1β production.