MR activation in macrophages is critical for the development of cardiac
inflammation and
fibrosis. We previously showed that MR activation modifies macrophage pro-inflammatory signalling, changing the cardiac tissue response to injury via both direct gene transcription and JNK/AP-1 second messenger pathways. In contrast, MR-mediated renal
electrolyte homeostasis is critically determined by
DNA-binding-dependent processes. Hence, ascertaining the relative contribution of MR actions via
DNA binding or alternative pathways on macrophage behaviour and cardiac
inflammation may provide therapeutic opportunities which separate the cardioprotective effects of MR antagonists from their undesirable renal
potassium-conserving effects. We developed new macrophage cell lines either lacking MR or harbouring a mutant MR incapable of
DNA binding. Western blot analysis demonstrated that MR
DNA binding is required for
lipopolysaccharide (LPS), but not
phorbol 12-myristate-13-acetate (PMA), induction of the MAPK/pJNK pathway in macrophages. Quantitative RTPCR for pro-inflammatory and pro-fibrotic targets revealed subsets of LPS- and PMA-induced genes that were either enhanced or repressed by the MR via actions that do not always require direct MR-
DNA binding. Analysis of the MR target gene and profibrotic factor MMP12 identified promoter elements that are regulated by combined MR/MAPK/JNK signalling. Evaluation of cardiac tissue responses to an 8-day DOC/
salt challenge in mice selectively lacking MR
DNA-binding in macrophages demonstrated levels of inflammatory markers equivalent to WT, indicating non-
DNA binding-dependent MR signalling in macrophages is sufficient for DOC/
salt-induced tissue
inflammation. Our data demonstrate that the MR regulates a macrophage pro-inflammatory phenotype and cardiac tissue
inflammation, partially via pathways that do not require
DNA binding.