Characterization of a PDZ domain-containing protein in macrophages

Abstract

Vulnerable atherosclerotic plaques are characterized by large necrotic cores and thin fibrous caps. Macrophage cell death is an important contributor to necrotic core size and high-density lipoprotein (HDL) has been shown to promote macrophage survival. Research has shown that HDL-dependent protection of macrophages is impaired in macrophages from Pdzk1 knockout mice. However, little is known on the expression of Pdzk1 in macrophages. In this study, we investigated Pdzk1 expression in macrophages and its role in HDL-dependent protection of macrophages against necroptosis. Real-time quantitative reverse-transcriptase polymerase chain reaction and Western blotting were conducted on macrophages from wild type and two different Pdzk1-targeted mutant mice. We show that Pdzk1 is expressed in macrophages. However, we also discovered that there is aberrant expression of truncated Pdzk1 transcript(s) in macrophages from a commonly used Pdzk1 global knockout mouse strain, although this was not the case in conditional Pdzk1 knockout macrophages from a different mouse strain. Our findings indicate that the null mutation in macrophages from Pdzk1 global knockout mice is not bona-fide and suggest for re-evaluation of the role of PDZK1 in HDL-signaling in macrophages. To investigate the role of PDZK1 in HDL-dependent protection of macrophages, we used conditional Pdzk1 knockout macrophages and demonstrated that PDZK1 indeed promotes HDL-dependent protection against necroptotic cell death. This study confirms that Pdzk1 is expressed in macrophages and clarifies its importance in HDL-dependent protection of macrophages from cell death.