Defects in TRPM7 channel function deregulate thrombopoiesis through altered cellular Mg2+ homeostasis and cytoskeletal architecture

Mg 2+ plays a vital role in platelet function, but despite implications for life-threatening conditions such as stroke or myocardial infarction, the mechanisms controlling [Mg 2+ ] i in megakaryocytes (MKs) and platelets are largely unknown. Transient receptor potential melastatin-like 7 channel (TRPM7) is a ubiquitous, constitutively active cation channel with a cytosolic α-kinase domain that is critical for embryonic development and cell survival. Here we report that impaired channel function of TRPM7 in MKs causes macrothrombocytopenia in mice ( Trpm7 fl/fl-Pf4Cre ) and likely in several members of a human pedigree that, in addition, suffer from atrial fibrillation. The defect in platelet biogenesis is mainly caused by cytoskeletal alterations resulting in impaired proplatelet formation by Trpm7 fl/fl-Pf4Cre MKs, which is rescued by Mg 2+ supplementation or chemical inhibition of non-muscle myosin IIA heavy chain activity. Collectively, our findings reveal that TRPM7 dysfunction may cause macrothrombocytopenia in humans and mice. Although Mg 2+ is vital for platelet activation and aggregation, its regulation in these cells is still largely unknown. Here, the authors show that TRPM7, a cation channel and a protein kinase, regulates thrombopoiesis and platelet size by affecting the cytoskeleton of these cells in mice and humans.