Parkinson's disease‐linked Kir4.2 mutation R28C leads to loss of ion channel function

<div xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="section"> <a class="named-anchor" id="tjp16752-sec-0010"> <!-- named anchor --> </a> <h5 class="section-title" id="d1470322e396">Abstract</h5> <p dir="auto" id="d1470322e398">Parkinson's disease (PD) is a complex, progressive neurodegenerative disorder driven by multiple pathogenetic factors, including oxidative stress, mitochondria dysfunction, neuroinflammation and ion imbalance. Recent evidence highlights the significant role of potassium channels in the pathophysiology of PD. We recently identified a PD‐linked genetic mutation in the <i>KCNJ15</i> gene ( <i>KCNJ15 ^p.R28C </i>), encoding the inwardly rectifying potassium channel Kir4.2, within a four‐generation family with familial PD. However, the role of the Kir4.2 channel in neurodegenerative diseases remains largely unexplored. This study aimed to elucidate the impact of the <i>KCNJ15 ^p.R28C </i> (Kir4.2 ^R28C) mutation on the biophysical and biochemical properties of Kir4.2. Employing Kir4.2‐overexpressing HEK293T cells as a model, we investigated how the mutation affects the channel's functional properties, total protein expression, intracellular processing in the endoplasmic reticulum and lysosomes and plasma membrane trafficking. Patch clamp studies revealed that the Kir4.2 ^R28C mutation results in loss of channel function with significant dominant‐negative effects. This dysfunction is partially attributed to the substantial reduction in overall mutant channel protein expression compared to the wild‐type (Kir4.2 ^WT). We observed that both Kir4.2 ^WT and Kir4.2 ^R28C proteins undergo glycosylation during the post‐translational modification process, albeit with differing protein turnover efficiencies. Furthermore, the Kir4.2 ^R28C mutant exhibits reduced stability and compromised plasma membrane trafficking capacity compared to Kir4.2 ^WT. These findings suggest that the Kir4.2 ^R28C mutant has unique biomolecular and biophysical characteristics distinct from the Kir4.2 ^WT channel, which potentially elucidates its role in the pathogenesis of PD. <div class="boxed-text panel" id="d1470322e444"> <a class="named-anchor" id="d1470322e444"> <!-- named anchor --> </a> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/8ea84a2c-fc21-4a94-8283-b0645dd1e762/PubMedCentral/image/TJP-603-3499-g008.jpg"/> </div> <div class="panel-content"/> </div> </p> </div><div xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="section"> <a class="named-anchor" id="tjp16752-sec-0020"> <!-- named anchor --> </a> <h5 class="section-title" id="d1470322e448">Key points</h5> <p dir="auto" id="d1470322e450"> <div class="list"> <a class="named-anchor" id="tjp16752-list-0001"> <!-- named anchor --> </a> <ul> <li id="d1470322e453"> <div class="so-custom-list-content so-ol"> <p class="first" dir="auto" id="d1470322e454">Inwardly rectifying potassium channels are increasingly recognized for their critical role in the complex pathogenesis of Parkinson's disease (PD). </p> </div> </li> <li id="d1470322e456"> <div class="so-custom-list-content so-ol"> <p class="first" dir="auto" id="d1470322e457">We previously identified a genetic mutation, Kir4.2 ^R28C, in the inwardly rectifying potassium channel Kir4.2, which strongly segregates with familial PD in a multi‐generational pedigree. </p> </div> </li> <li id="d1470322e462"> <div class="so-custom-list-content so-ol"> <p class="first" dir="auto" id="d1470322e463">This study confirms Kir4.2 ^R28C as a loss‐of‐function mutation with significant dominant‐negative effects, impairing channel activity even in heterozygous conditions. </p> </div> </li> <li id="d1470322e468"> <div class="so-custom-list-content so-ol"> <p class="first" dir="auto" id="d1470322e469">The Kir4.2 ^R28C mutation significantly reduces overall protein levels, impairs protein stability and disrupts plasma membrane trafficking in <i>in vitro</i> cell models. </p> </div> </li> </ul> </div> </p> </div><p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" dir="auto" id="d1470322e479"> <b>Abstract figure legend</b> Pathogenic impact of the PD‐linked Kir4.2 ^R28C mutation on Kir4.2 channel proteostasis and function. The Kir4.2 ^R28C mutation, identified in a familial Parkinson's disease (PD) pedigree, leads to a near‐complete loss of potassium channel function and exerts a significant dominant‐negative effect. Wild‐type Kir4.2 (Kir4.2 ^WT) is synthesized in the endoplasmic reticulum (ER), undergoes glycosylation and proper folding and is trafficked to the plasma membrane, where it forms functional potassium channels that mediate K ⁺ conductance. A proportion of Kir4.2 ^WT is also degraded via the lysosomal pathway. In contrast, the mutant Kir4.2 ^R28C exhibits impaired protein stability and maturation, resulting in reduced overall protein levels. The mutant channels are inefficiently trafficked to the plasma membrane and are unable to form functional channels, thereby disrupting potassium homeostasis. This combination of loss‐of‐function and dominant‐negative effects may contribute to the molecular pathogenesis of PD. <div class="boxed-text panel" id="d1470322e503"> <a class="named-anchor" id="d1470322e503"> <!-- named anchor --> </a> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/8ea84a2c-fc21-4a94-8283-b0645dd1e762/PubMedCentral/image/TJP-603-3499-g008.jpg"/> </div> <div class="panel-content"/> </div> </p>