LIM and SH3 protein 1 (LASP‐1): A novel link between the slit membrane and actin cytoskeleton dynamics in podocytes

Abstract

The foot processes of podocytes exhibit a dynamic actin cytoskeleton, which maintains their complex cell structure and antagonizes the elastic forces of the glomerular capillary. Interdigitating secondary foot processes form a highly selective filter for proteins in the kidney, the slit membrane. Knockdown of slit membrane components such as Nephrin or Neph1 and cytoskeletal adaptor proteins such as CD2AP in mice leads to breakdown of the filtration barrier with foot process effacement, proteinuria, and early death of the mice. Less is known about the crosstalk between the slit membrane‐associated proteins and cytoskeletal components inside the podocyte foot processes. Our study shows that LASP‐1, an actin‐binding protein, is highly expressed in podocytes. Electron microscopy studies demonstrate that LASP‐1 is found at the slit membrane suggesting a role in anchoring slit membrane components to the actin cytoskeleton. Live cell imaging experiments with transfected podocytes reveal that LASP‐1 is either part of a highly dynamic granular complex or a static, actin cytoskeleton‐bound protein. We identify CD2AP as a novel LASP‐1 binding partner that regulates its association with the actin cytoskeleton. Activation of the renin‐angiotensin‐aldosterone system, which is crucial for podocyte function, leads to phosphorylation and altered localization of LASP‐1. In vivo studies using the Drosophila nephrocyte model indicate that Lasp is necessary for the slit membrane integrity and functional filtration.

The podocyte-specific knockout of palladin in mice with a 129 genetic background affects podocyte morphology and the expression of palladin interacting proteins

“…However, the phosphorylation of Lasp-1 was significantly reduced. This might influence the stability of the podocyte foot processes, since it was already shown that phosphorylation of Lasp-1 reduces the binding to F-actin in vitro [ 16 , 50 ].…”

LIM-Nebulette Reinforces Podocyte Structural Integrity by Linking Actin and Vimentin Filaments

“…During the peer-review of this manuscript, a comprehensive study was published, investigating the role of the protein Lasp-1 in linking the slit diaphragm with the actin cytoskeleton in podocytes. 50 Lasp-1 is a key paralog of LIM-nebulette (also known as Lasp-2), which is the podocyte-specific isoform studied herein. It should be noted that although the second isoform of nebulette is also called Lasp-2, it is completely unrelated to the protein Lasp-1, which is encoded by the gene LASP1.…”

LASP1 in Cellular Signaling and Gene Expression: More than Just a Cytoskeletal Regulator

“…In podocytes, LASP1 is crucial for the slit membrane integrity and glomerular filtration. Activation of the renin-angiotensin-aldosterone system by Ang II, significantly increased pS146-LASP1 phosphorylation by PKA and resulted in a re-localization of the protein from along intracellular actin stress fibers to the lamellipodia at the outer cell membrane thereby anchoring slit membrane components like CD2AP to the actin cytoskeleton through an interaction with the SH3 domain [ 61 ]. Nephrocyte-specific knockdown of Lasp in Drosophila melanogaster showed reduced number of slit membranes and mislocalization of F-actin [ 61 ].…”

“…Activation of the renin-angiotensin-aldosterone system by Ang II, significantly increased pS146-LASP1 phosphorylation by PKA and resulted in a re-localization of the protein from along intracellular actin stress fibers to the lamellipodia at the outer cell membrane thereby anchoring slit membrane components like CD2AP to the actin cytoskeleton through an interaction with the SH3 domain [ 61 ]. Nephrocyte-specific knockdown of Lasp in Drosophila melanogaster showed reduced number of slit membranes and mislocalization of F-actin [ 61 ]. This is in agreement with a second study by Artelt et al, showing that a podocyte-specific knockdown of Palladin, a LASP1 binding partner along actin stress fibers [ 62 ], leads to a decreased pLasp1 phosphorylation and morphological deviations like an enlarged sub-podocyte space [ 63 ].…”