Similar Biophysical Abnormalities in Glomeruli and Podocytes from Two Distinct Models

Abstract

FSGS is a pattern of podocyte injury that leads to loss of glomerular function. Podocytes support other podocytes and glomerular capillary structure, oppose hemodynamic forces, form the slit diaphragm, and have mechanical properties that permit these functions. However, the biophysical characteristics of glomeruli and podocytes in disease remain unclear. Using microindentation, atomic force microscopy, immunofluorescence microscopy, quantitative RT-PCR, and a three-dimensional collagen gel contraction assay, we studied the biophysical and structural properties of glomeruli and podocytes in chronic (Tg26 mice [HIV protein expression]) and acute (protamine administration [cytoskeletal rearrangement]) models of podocyte injury. Compared with wild-type glomeruli, Tg26 glomeruli became progressively more deformable with disease progression, despite increased collagen content. Tg26 podocytes had disordered cytoskeletons, markedly abnormal focal adhesions, and weaker adhesion; they failed to respond to mechanical signals and exerted minimal traction force in three-dimensional collagen gels. Protamine treatment had similar but milder effects on glomeruli and podocytes. Reduced structural integrity of Tg26 podocytes causes increased deformability of glomerular capillaries and limits the ability of capillaries to counter hemodynamic force, possibly leading to further podocyte injury. Loss of normal podocyte mechanical integrity could injure neighboring podocytes due to the absence of normal biophysical signals required for podocyte maintenance. The severe defects in podocyte mechanical behavior in the Tg26 model may explain why Tg26 glomeruli soften progressively, despite increased collagen deposition, and may be the basis for the rapid course of glomerular diseases associated with severe podocyte injury. In milder injury (protamine), similar processes occur but over a longer time.

Disruption of podocyte cytoskeletal biomechanics by dasatinib leads to nephrotoxicity

“…We recently showed that regulators of YAP spatial activity, such as KIBRA, play a critical role in organization of the actin cytoskeleton in podocytes 41 . Recently, biomechanical integrity of podocytes had been proposed as a coherent signature that underlies multiple glomerular disease models 42 , supporting our hypothesis that drugs that challenge the actin cytoskeleton architecture in podocytes may induce glomerular dysfunction and nephrotoxicity. We also note that while our in vitro assays were extensive, covering a varying range of time and concentration values for dasatinib and the other KIs, the dynamics of the podocyte kinome that controls the actin cytoskeleton is clearly complex, and it needs to be studied in further detail.…”

Substrate Stiffness Modulates Renal Progenitor Cell Properties via a ROCK-Mediated Mechanotransduction Mechanism

“…This was an unexpected result, as one would predict glomeruli at early stages of disease to be normal and then stiffen with progressive sclerosis. Similarly, Embry et al [27] reported that in Tg26 HIV/nl mice, glomeruli soften progressively despite an increased collagen deposition. This observation could be in agreement with our demonstration of increased mRNA levels of ECM components in RPCs cultured on softer substrates.…”

“…In particular, the mechanical elasticity of the substrate, or stiffness, is a physical property defined as force per unit area divided by deformation (Young's modulus, E) that greatly affects cell activity in vitro [23][24][25] and in vivo, during development, in tissue homeostasis, and in disease progression [26]. In the kidney, the mechanical environment is subjected to modifications in established models of glomerular diseases [27] and can affect the differentiated state of numerous cell types, including podocytes [28][29][30][31].…”

Nephrotoxicity Associated with Novel Anticancer Agents (Aflibercept, Dasatinib, Nivolumab): Case Series and Nephrological Considerations

“…Podocytes have exceptionally fragile cytoskeletal dynamics [ 43 ], and the loss of their biomechanical integrity may represent a consistent signature underlying many glomerular disease models [ 44 ]. Dasatinib could induce glomerular toxicity through a direct effect on the structural integrity of podocyte cytoskeleton, leading to decreased cellular elasticity impinging on its key function as a structural member of the filtration barrier [ 28 ].…”