Our Research
We are a team of molecular biologists, cell physiologists, and kidney-oriented physicians who aim to understand how salt and water homeostasis is regulated from cell to organism. Most of our work is centered on the WNK-SPAK/OSR1 pathway, a network of serine-threonine kinases that control cell fluid volume and size through the sensing of intracellular molecular crowding and ionic strength. During evolution, these regulatory mechanisms were co-opted to control transcellular ion and fluid movement in epithelia, and ultimately, clinically relevant processes such as blood pressure and potassium balance. A fundamental principle that drives our work centers around unraveling how ion transport is regulated in cells; we strive to understand these processes in an effort to translate them to kidney physiology and clinical practice.
WNK Kinases as Phase Separating Crowding Sensors
In 2022, we reported that WNK kinases regulate cell volume by sensing and responding to the molecular crowding that occurs within cells during exposure to hypertonicity. They do so by undergoing phase separation into biomolecular condensates: membrane-less droplet-like assemblies that function as activation hubs for the WNK signaling pathway. Following condensate-mediated activation, the WNK signaling pathway leaves the droplet phase and phosphorylates salt cotransporters at the plasma membrane, resulting in a net influx of ions and volume recovery within minutes. Many aspects of this activation mechanism remain unresolved, and this is a major focus of our current work. We are also interested in elucidating the role of molecular crowding in the control of ion transport in polarized epithelial cells. In these studies, quantitative live cell imaging of WNK phase behavior is coupled to live cell volume measurements during hypertonic stress and biochemical analysis of cell signaling. By using this multifaceted approach, we are able to unravel how phase transitions in the WNK signaling pathway affect physiological function.
Distal Tubule WNK Bodies and Potassium Homeostasis
Potassium is the most abundant intracellular cation and is necessary for existence, as it participates in critical biological processes, including neuronal and cardiac function, and in the control of cell volume and systemic blood pressure. However, since even slight fluctuations of extracellular potassium outside of the normal range can be lethal, the ingestion of a dietary potassium load presents a daily challenge for mammals. The kidney regulates total body potassium balance and WNK kinases are essential for this process. During hypokalemia (low potassium levels in the blood), a specific complement of WNKs expressed in the distal convoluted tubule localizes into large discrete puncta. In 2017, we extensively characterized these foci, reported that they are membraneless, and discovered that their formation requires a DCT-specific isoform of the WNK1 gene termed KS-WNK1. We therefore opted to name them “WNK Bodies”, adopting terminology reminiscent of other biomolecular condensates present in cells. We are now conducting studies to determine whether WNK bodies are necessary for the kidney to conserve potassium during states of dietary K+ deficiency. This work involves a combination of high resolution live cell and fixed kidney imaging, biochemical measurements of kidney tubule-specific WNK signaling, dietary and pharamcologic maneuvers in KS-WNK1 mutant mice, and whole animal physiology.
Support
Our research is supported by the National Institutes of Health and the US Department of Veterans Affairs.
