Michelle Christina Johansen, MD

Begum G, Yuan H, Kahle KT, Li L, Wang S, Shi Y, et al. Inhibition of WNK3 Kinase Signaling Reduces Brain Damage and Accelerates Neurological Recovery After Stroke. Stroke. 2015 

Research targeting experimental stroke provides the foundation for future initiatives that lead to clinical implementation. Begum et al in their study investigate the WNK3-SPAK/OSR1 pathway in order to determine the role it plays in regulation of the bumetanide-sensitive Na-K-Cl cotransporter (NKCC1). This cotransporter has been shown to play an important role in the pathophysiology of experimental stroke but its exact mechanism has remained yet unexplained. By way of brief review, WNK3 (with no lysine) is a kinase that activates SPAK/OSR1 which in turn stimulates NKCC1. A similar pathway has been well researched in renal epithelial homeostasis but not in the brain. In vitro, inactivated WNK3 is a potent inhibitor of NKCC1 thus making it an attractive target for research. 

In their experiment, WNK3 wild-type (WT) and knockout (KO) mice were subjected to ischemic stroke via MCA occlusion for 60 minutes. Sensorimotor neurological deficit in the mice were evaluated post stroke. Infarct volume and hemispheric swelling was calculated postmortem and wet weight of the tissue was measured. A total of 61 mice were used in the study. All measurements were performed by investigators who were blinded to the study.

The researchers found that there was no difference in regional cerebral blood flow in the WNK3 KO and WNK3 WT littermates after MCA occlusion but after 24h of reperfusion, KO brains exhibited a marked reduction in cortical infarct volume relative to the wild type. Smaller infarcts were also noted in KO at 3 days post MCA occlusion by MRI and exhibited significantly less demyelination of the external capsule white matter tracks. This was shows to have ramifications functionally as KO mice exhibited accelerated recovery. There was decreased hemispheric swelling and albumin infiltration in KO mice. The investigators founds that focal cerebral ischemia activates NKCC1 by the WNK and SPAK/OSRI kinases and that this signaling pathway was regulated differently depending on brain region and cell type. No ischemic cell death was evident in untreated WNK3 KO neurons or in those treated with SPAK/OSR1 siRNAs (silencing RNAs).

The authors conclude that genetic inactivation of WNK3 or siRNA-mediated knockdown of SPAK/OSRI prevents demyelination and reduces primary oligodendrocyte death highlighting that this signaling complex serves as a potential target for neuroprotection and preservation of myelination following stroke. The team should be commended for working to elucidate the WNK3 pathway in the cerebrum. While this work is in its infantile state, one can only hope that WNK3 inhibition in the clinical setting would yield similar results.