Reduced podocyte stiffness is a feature of proteinuric kidney disease

Proteinuria is a common and important manifestation of glomerular injury. Although the molecular events driving proteinuria have been studied extensively, the biomechanical changes that occur in the glomerulus remain largely unexplored.

Using in situ atomic force microscopy on kidney tissue from murine glomerular disease models (Akita^+/- Ren^+/-, Col4a5^-/Y, and Myo1e^-/- vs controls) and human biopsies (focal segmental glomerulosclerosis vs transplant donors as controls), the stiffness of glomeruli, podocytes, and glomerular basement membranes was analyzed. We also measured the expression and/or localization of beta1 integrin and the two mechanosensitive transcription co-factor proteins YAP and TAZ using immunofluorescence staining.

We show that the stiffness of glomeruli and various glomerular components changes in response to various forms of kidney injury. These changes are often opposing in nature and likely reflect underlying disease-specific processes. Our case-control studies revealed that podocyte softening is a common feature of proteinuric kidney diseases in humans and mice, even when podocytes sit upon a thickened and stiffer glomerular basement membrane. Furthermore, in the setting of proteinuria, podocytes express lower levels of beta1 integrin, a critical molecule used by podocytes to adhere to the glomerular basement membrane. Moreover, beta1 integrin inhibition results in podocyte softening, and this softening is associated with inactivation of YAP and TAZ, two mechanosensitive transcription co-factors that are critical for maintaining podocyte health. Finally, YAP/TAZ inhibition leads to lower beta1 integrin expression.

Our results demonstrate that glomeruli and their components undergo dramatic and often divergent stiffness changes following different types of injury. Interestingly, podocyte softening is a common manifestation of proteinuric kidney diseases, a phenomenon that is associated with inactivation of transcription co-factors that maintain normal podocyte structure and function.