Tyrosine Phosphorylation of CD2AP Affects Stability of the Slit Diaphragm Complex.

Background: CD2-associated protein (CD2AP), a slit diaphragm-associated scaffolding protein involved in survival and regulation of the cytoskeleton in podocytes, is considered a "stabilizer" of the slit diaphragm complex that connects the slit diaphragm protein nephrin to the cytoskeleton of the cell. Tyrosine phosphorylation of slit diaphragm molecules can influence their surface expression, but it is unknown whether tyrosine phosphorylation events of CD2AP are also physiologically relevant to slit diaphragm stability.

Methods: We used isoelectric focusing, western blot analysis, and immunofluorescence to investigate phosphorylation of CD2AP, and phospho-CD2AP antibodies and site-directed mutagenesis to define the specific phosphorylated tyrosine residues.

Def-6, a novel regulator of small GTPases in podocytes, acts downstream of atypical protein kinase C (aPKC) λ/ι.

The atypical protein kinase C (aPKC) isotypes PKCλ/ι and PKCζ are both expressed in podocytes; however, little is known about differences in their function. Previous studies in mice have demonstrated that podocyte-specific loss of PKCλ/ι leads to a severe glomerular phenotype, whereas mice deficient in PKCζ develop no renal phenotype. We analyzed various effects caused by PKCλ/ι and PKCζ deficiency in cultured murine podocytes.

aPKCλ/ι and aPKCζ contribute to podocyte differentiation and glomerular maturation.

Precise positioning of the highly complex interdigitating podocyte foot processes is critical to form the normal glomerular filtration barrier, but the molecular programs driving this process are unknown. The protein atypical protein kinase C (aPKC)--a component of the Par complex, which localizes to tight junctions and interacts with slit diaphragm proteins--may play a role. Here, we found that the combined deletion of the aPKCλ/ι and aPKCζ isoforms in podocytes associated with incorrectly positioned centrosomes and Golgi apparatus and mislocalized molecules of the slit diaphragm.

Deficits in sialylation impair podocyte maturation.

The role of sialylation in kidney biology is not fully understood. The synthesis of sialoglycoconjugates, which form the outermost structures of animal cells, requires CMP-sialic acid, which is a product of the nuclear enzyme CMAS. We used a knock-in strategy to create a mouse with point mutations in the canonical nuclear localization signal of CMAS, which relocated the enzyme to the cytoplasm of transfected cells without affecting its activity.

Impact of high glucose and transforming growth factor-β on bioenergetic profiles in podocytes.

Diabetic nephropathy is the most common cause of chronic renal failure in industrialized countries. Depletion of podocytes plays an important role in the progression of diabetic glomerulopathy. Various factors in the diabetic milieu lead to serious podocyte stress driving the cells toward cell cycle arrest (p27(Kip1)), hypertrophy, detachment, and apoptosis.

CD2AP regulates SUMOylation of CIN85 in podocytes.

Podocytes are highly differentiated and polarized epithelial cells located on the visceral side of the glomerulus. They form an indispensable component of the glomerular filter, the slit diaphragm, formed by several transmembrane proteins and adaptor molecules. Disruption of the slit diaphragm can lead to massive proteinuria and nephrotic syndrome in mice and humans.

The role of metabolic and haemodynamic factors in podocyte injury in diabetes.

Podocyte loss is a common feature in human diabetes as well as in experimental diabetes in rodents. Almost all components of the diabetic milieu lead to serious podocyte stress, driving the cells towards cell cycle arrest and hypertrophy, detachment and apoptosis. Common pathway components induced by high glucose and advanced glycation end-products are reactive oxygen species, cyclin-dependent kinases (p27(Kip1)) and transforming growth factor-beta.

CIN85/RukL is a novel binding partner of nephrin and podocin and mediates slit diaphragm turnover in podocytes.

Podocyte damage is the basis of many glomerular diseases with ultrastructural changes and decreased expression of components of the slit diaphragm such as nephrin and podocin. Under physiological conditions it is likely that the slit diaphragm underlies permanent renewal processes to indemnify its stability in response to changes in filtration pressure. This would require constant reorganization of the podocyte foot process and the renewal of slit diaphragm components.

Urinary excretion of IGFBP-1 and -3 correlates with disease activity and differentiates focal segmental glomerulosclerosis and minimal change disease.

The glomerular microenvironment is influenced by circulating growth factors that are filtered from the blood stream and pass the glomerular filtration barrier. In this study, we wanted to explore the role of IGF-binding proteins (IGFBPs) in two diseases that concern podocytes. We analyzed glomerular expression and urinary excretion of IGFBP-1, -2, and -3 in patients with focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD).

The balance of autocrine VEGF-A and VEGF-C determines podocyte survival.

Podocytes are an important component of the glomerular filtration barrier and are the major source of vascular endothelial growth factor (VEGF) in the glomerulus. The role of VEGF for the phenotype of the glomerular endothelium has been intensely studied; however, the direct effects of autocrine VEGF on the podocyte are largely unknown. In this study we characterized the expression of VEGF isoforms and VEGF receptors in cultured human podocytes and examined direct effects on cell signaling and apoptosis after stimulation with exogenous VEGF or ablation of autocrine VEGF.