Abstract Ion channels, transporters, exchangers and pumps (here called ICTs) control most aspects of life. They have been extensively characterized in excitable cells, such as neurons, where they control neurotransmitter release and other functions as well as cardiac and skeletal muscle cells, where they regulate the strength of contraction. In most non-excitable cells, and specifically in immune cells, ICTs are only scantly characterized. We have taken a global approach to analyze the expression of more than 600 ICTs in immune cells, and observed that one particular putative ICT, named FAM26F, is highly and specifically expressed in proinflammatory macrophages compared to other immune cells. FAM26F is an understudied ion channel that belongs to a small family of proteins (FAM26A to F). The best characterized FAM26 family member is FAM26C. It functions as an ion channel under certain experimental conditions and has been described to promote ATP release from cells. Recently published low resolution structures of FAM26F show that it, like FAM26C, also forms a pore and may act as an ion channel. Our preliminary data to date, however, did not detect evidence for channel function of FAM26F when overexpressed in mammalian cells. The most likely reason is that FAM26F needs other subunits or associated proteins to function as a channel, which is characteristic of many ion channels. We hypothesize that while overexpression of FAM26F may not be sufficient to generate a functional channel, and proinflammatory macrophages express not only FAM26F but also the other proteins required to form a channel. To test this hypothesis, we will in Aim 1 directly measure putative functions of FAM26F such as channel currents and the transport of low molecular weight molecules. In a parallel approach, we will use biochemical methods and mass spectrometry to identify the proteins that associate with FAM26F in macrophages. In Aim 2, we will elucidate the role of FAM26F in macrophage function and inflammation. Our preliminary data have shown that deletion of FAM26F impairs certain proinflammatory functions of macrophages such as the release of cytokines. These immune messenger proteins are critical for disease progression in the autoimmune disease rheumatoid arthritis, where they drive joint inflammation and destruction. We will therefore use macrophages and mice in which FAM26F has been deleted to determine the effects of FAM26F on macrophage function in cell culture settings and in mouse models of rheumatoid arthritis. This multi-PI R03 proposal by Drs. Stefan Feske and William Coetzee brings together their unique expertise to better understand the roles of channels, and in particular FAM26F, in innate immunity. There are currently no FDA approved drugs that target ion channels for immunological disorders and the completion of the proposed studies takes us an important step in the direction of this missed therapeutic opportunity.

Narrative Ion channels, transporters, exchangers and pumps control most aspects of life, but they are poorly characterized in immune cells. We have identified FAM26F, a novel putative channel, to be specifically expressed in proinflammatory macrophages, which we will study using a combination of cellular assays of macrophage function and mouse models of rheumatoid arthritis, an autoimmune disease in which macrophages play an important driving disease progression. This research has the potential to further our understanding of ion channels in immune cells, and to identify new targets for the immunotherapy of rheumatoid arthritis.