Macrophage ion channels as anti-inflammatory drug targets

Macrophages play a key role in immune responses to invading pathogens. They engulf and destroy microorganisms and present the resultant antigens to lymphocytes to incite adaptive immune responses. A key aspect of their regulatory role is the production of cytokines to recruit other immune cells to sites of inflammation. Though beneficial in combating infection, cytokine excess can contribute to aberrant inflammation that damages the body’s own tissues. Macrophages contain a diverse set of ion channels that regulate their functions. In recent decades, evidence has emerged that some of these ion channels may represent possible drug targets for tempering macrophage-driven immune responses, but more work is needed to (1) identify more selective drugs that can target macrophage ion channels and (2) fully elucidate the downstream signaling and activation modalities involved. This thesis presents two projects furthering these goals. The first involved the development and in vivo demonstration of new TRPM7 inhibitors. TRPM7 is an ion channel which plays a role in inflammatory cytokine production and genetic knockout of the channel provides protection to mice in an LPS-induced sepsis model. But a shortage of suitable TRPM7 inhibitors prevented the validation of TRPM7 as an immunomodulatory drug target in pharmacological studies. The first project demonstrated that VPC01091.4 and AAL-149 are inhibitors of TRPM7 which reproduce the effects of TRPM7 knockout in a mouse model of LPS-induced sepsis. The second project dissects the pathways involved in oxidized phospholipid driven Ca2+ signaling in macrophages. Atherosclerosis is increasingly recognized as a chronic inflammatory disease, and the response of macrophages to oxidized phospholipids may play a key role in the disease pathogenesis. Here we demonstrate that OxPLs activate several pathways of cytosolic Ca2+ signaling in macrophages. These include Syk- and PLC-dependent ER Ca2+ release and subsequent Orai1-dependent store operated Ca2+ entry from the extracellular environment. We also demonstrate that OxPLs directly activate plasma membrane TRPV4, which contributes approximately 50% of total extracellular Ca2+ entry. More work is needed to identify the downstream inflammatory consequences to inhibiting these pathways for OxPL-induced Ca2+ signaling but targeting of these pathways may eventually allow for modulation of the atherogenic response to OxPLs and OxPL-rich lipid particles.