A mutation in the Na‐K‐2Cl cotransporter‐1 leads to changes in cellular metabolism

Abstract

The Na-K-Cl cotransporter-1 (NKCC1), by mediating the electroneutral transport of Na + , K + , and Cl − plays an important role in cell volume regulation, epithelial transport, and the control of neuronal excitability. Recently, we reported the first known human mutation in SLC12A2, the gene encoding NKCC1. The 17-year old patient suffers from multiorgan failure. Laboratory tests conducted on muscle and liver biopsies of the patient showed abnormal increase in mitochondrial DNA copy number and increased glycogen levels, indicating the possibility that the transporter may play a role in energy metabolism. Here, we show that fibroblasts isolated from the patient demonstrate a significant increase in mitochondrial respiration, compared to fibroblasts isolated from healthy individuals. Similarly, Madin Darby canine kidney (MDCK) cells transfected with enhanced green fluorescent protein (EGFP)tagged mutant NKCC1 DNA demonstrated increased mitochondrial respiration when compared to MDCK cells expressing EGFP-tagged wild-type (WT) cotransporter. Direct inhibition of the cotransporter through addition of bumetanide did not change the rate of basal respiration, but led to increased maximal mitochondrial respiration. Fibroblasts extracted from NKCC1 WT/DFX and NKCC1 DFX/DFX mice also demonstrated a significant elevation in mitochondrial respiration, compared to fibroblasts isolated from their WT littermates. Expression of the mutant protein was associated with an increase in hydrogen peroxide and peroxidase activity and a decrease in messenger RNA transcript levels for protein involved in the unfolded protein response. These data reveal that cells expressing the mutant cotransporter demonstrate increased mitochondrial respiration and behave like they are experiencing a state of starvation.

Sodium Transporters in Human Health and Disease

“…Increased activation of the nutrient/energy sensor, mTORC1 is consistent with the increased need for mitochondrial respiration that we observed in cells isolated from the NKCC1-DFX patient and in cells from mice expressing the same mutant transporter (Omer et al, 2020). If NKCC1 functions as a break to the amino acid transporter LAT1 and to the insulin receptor, in macrophages, it also provides a break to the function of phagocytosis (Perry et al, 2019).…”

“…The mouse exhibited mis-trafficking of the cotransporter to the apical membrane of epithelial cells, decreased intestinal function due to deficit in luminal hydration, deficit in release and expansion of mucus layers (Koumangoye et al, 2020). As surprising, was our demonstration that cells from the mouse had increased mitochondrial respiration, and signs of starvation (Omer et al, 2020).…”

NKCC1: Newly Found as a Human Disease-Causing Ion Transporter

“…Remarkably, fibroblasts isolated from NKCC1 knockout mice also displayed significant increases in ROS, as established through increase in hydrogen peroxide production and peroxidase activity. 89 These data indicate that the phagocyte phenotype switch might be extendable to other cell types.…”

“…Yet, when the patient fibroblasts were used to measure mitochondrial respiration, the rate of oxygen consumption was significantly higher in the patient fibroblasts, compared to fibroblasts isolated from healthy controls. 89 …”

WNK1 enforces macrophage lineage fidelity

“…5k Our findings raise several interesting questions. For instance, previous studies suggest that macropinocytosis facilitates nutrient uptake 64 , and a recent report found that mutation of SLC12A2, a chloride transporter regulated by WNK1, causes altered cellular metabolism 65 . Does WNK1 regulate cellular metabolism downstream of macropinocytosis?…”