Piezo, Nephrocyte Function, and Slit Diaphragm Maintenance in Drosophila.

KEY POINTS: Piezo channels, known for detecting mechanical pressure, were found to be expressed at the lacuna channel membranes of nephrocytes. Piezo loss of function caused nephrocyte dysfunction, including disrupted slit diaphragm structure and altered lacuna channel morphology. Piezo deficiency led to internalized slit diaphragm proteins, reduced autophagy, increased endoplasmic reticulum stress, and impaired calcium homeostasis. BACKGROUND: The Piezo gene encodes a highly conserved cell membrane protein responsible for sensing pressure. The glomerular kidney and the slit diaphragm filtration structure depend on pressure for filtration. However, how Piezo is involved in kidney function and in maintaining the slit diaphragm filtration structure is not clear. METHODS: We used Drosophila pericardial nephrocytes, filtration kidney cells with striking structural and functional similarities to human podocytes, in a loss-of-function model (mutant and knockdown) to study the roles of Piezo in nephrocyte filtration and function. RESULTS: Piezo was highly expressed at the invaginated membranes (lacuna channels) of nephrocytes. A Piezo loss-of-function mutant showed significant nephrocyte functional decline. Nephrocyte-specific silencing of Piezo showed disruption of the slit diaphragm filtration structure and significant functional defects. Electron microscopy showed that silencing Piezo in nephrocytes led to reduced slit diaphragm density and abnormal shape of lacuna channels. Moreover, the Piezo-deficient nephrocytes showed internalized slit diaphragm component proteins, reduced autophagy, increased endoplasmic reticulum stress, and reduced calcium influx. CONCLUSIONS: Together, our findings suggest that Piezo plays an important role in the calcium homeostasis of nephrocytes and is required for maintaining nephrocyte function and the slit diaphragm filtration structure.