Parkinson’s Disease-Linked Kir4.2 Mutation R28C Leads to Loss of Ion Channel Function

Abstract

Parkinson's disease (PD) is a complex progressive neurodegenerative disorder involving multiple pathogenetic factors, including oxidative stress, mitochondria dysfunction, neuroinflammation, and ion imbalance. Emerging evidence underscores the significant role of potassium channels in multiple aspects of PD etiology. We recently identified a PD-linked genetic mutation in the KCNJ15 gene (KCNJ15p.R28C), encoding the inwardly rectifying potassium channel Kir4.2, within a four-generation family with familial PD. The role of the Kir4.2 channel, especially in neurodegenerative diseases, remains largely unexplored. This study aimed to elucidate the impact of the KCNJ15p.R28C (Kir4.2R28C) mutation on the biophysical and biochemical properties of Kir4.2. Employing Kir4.2-overexpressing HEK293T cells as our model, we investigated how the mutation affects the channel's biophysical properties, total protein expression, endoplasmic reticulum and lysosome processing, and plasma membrane trafficking. Patch clamp studies revealed that the Kir4.2R28C mutation results in loss of channel function, exhibiting a strong dominant-negative effect. This can be partially attributed to the significantly diminished overall expression of the mutant channel protein compared to the wild-type (Kir4.2WT). We observed that both Kir4.2WT and Kir4.2R28C proteins undergo glycosylation during the post-translational modification process, albeit with differing protein turnover efficiencies. Furthermore, the KCNJ15p.R28C mutation exhibits reduced stability compared to Kir4.2WT and is more susceptible to protein recycling through the lysosomal degradation pathway. Additionally, Kir4.2R28C displayed reduced plasma membrane trafficking capacity compared to Kir4.2WT. These findings suggest that the Kir4.2R28C mutant possesses unique biomolecular and biophysical characteristics distinct from the Kir4.2WT channel, which potentially elucidates its role in the pathogenesis of PD.