Platelet transfusions are indispensable in treating bleeding disorders and supporting patients undergoing chemotherapy or surgery. However, donor shortages and the short shelf life of platelets—just 4 to 7 days—pose significant logistical and clinical challenges. Researchers in the Eto Laboratory previously developed immortalized megakaryocyte progenitor cell lines (imMKCLs) derived from human iPS cells for scalable ex vivo platelet production. Recently, they investigated the molecular mechanisms underlying platelet biogenesis, focusing on the role of potassium ion (K⁺) channels, particularly KCNN4, the gene encoding K_Ca3.1, a calcium ion (Ca²⁺)-activated K⁺ channel.

Using imMKCLs and human cord blood-derived megakaryocyte (CB-MK), the team observed a consistent decline in intracellular K⁺ concentration during the six-day maturation (Dox-OFF) stage. RNA sequencing revealed that KCNN4 expression peaked at the onset of platelet generation. Functional inhibition or gene knockdown of KCNN4 significantly impaired proplatelet formation and reduced platelet yield in both cell types. These effects were accompanied by disrupted microtubule organization, decreased mitochondrial membrane potential (MMP), and elevated reactive oxygen species (ROS), indicating a breakdown in cellular homeostasis.

Microscopic and flow cytometric analyses showed that KCNN4 inhibition caused asymmetric tubulin accumulation and mitochondrial dysfunction, leading to excessive ROS levels. This oxidative stress interfered with microtubule dynamics essential for cytoplasmic extensions forming proplatelets. Treatment with the ROS inducer tert-butyl hydroperoxide (TBHP) replicated these effects, confirming the role of ROS in suppressing platelet production. Importantly, these disruptions occurred without affecting cell viability or ploidy, suggesting a specific impact on the maturation process rather than general toxicity.

KCNN4 was shown to be especially critical during the early stages of megakaryocyte maturation. Inhibitors applied during the first two days of the Dox-OFF stage had the most pronounced impact on platelet output, highlighting a narrow but crucial window for ion channel activity. KCNN4 knockdown also prevented the physiological decline of intracellular K⁺ concentration, further linking K⁺ efflux to mitochondrial and cytoskeletal regulation.

This study identifies KCNN4 as a key regulator of thrombopoiesis by maintaining mitochondrial integrity and ROS balance. The findings illuminate a previously underappreciated molecular pathway in platelet biogenesis and suggest strategies to enhance ex vivo platelet production. These insights may also inform future therapies for thrombocytopenic disorders and improve the reliability of platelet supply for transfusion medicine.

• doi: 10.1016/j.jtha.2025.05.013