Expression of galectin-1, a new component of slit diaphragm, is altered in minimal change nephrotic syndrome

Abstract

Nephrin is an essential structural component of the glomerular slit diaphragm (SD), a highly organized intercellular junction that constitutes the ultrafiltration barrier of the kidney. Recent studies have identified two additional nephrininteracting SD proteins (NEPH1 and NEPH2), suggesting that the zipper-like pattern of the SD is formed through complex intra-and intermolecular interactions of these proteins. However, the complexity of the SD structure suggests that additional SD components remain to be discovered. In this study, we identified galectin-1 (Gal-1) as a new component of the SD, binding to the ectodomain of nephrin. Using dual-immunofluorescence and confocal microscopy and dual-immunoelectron microscopy, we found Gal-1 colocalizing with the ectodomain of nephrin at the SD in normal human kidney. By immunoprecipitation and surface plasmon resonance, we confirmed a direct molecular interaction between Gal-1 and nephrin. Moreover, recombinant Gal-1 induced tyrosine phosphorylation of the cytoplasmic domain of nephrin and activation of the extracellular signal-regulated kinase 1/2 in podocytes. We also showed that podocytes are a major site of biosynthesis of Gal-1 in the glomerulus and that the normal expression patterns and levels of Gal-1 are altered in patients with minimal change nephrotic syndrome. Finally, in puromycin aminonucleoside-induced rat nephrosis, an apparent reduction in the levels of Gal-1 and nephrin around the onset of heavy proteinuria was also revealed. Our data present Gal-1 as a new extracellular ligand of nephrin localized at the glomerular SD, and provide further insight into the complex molecular organization, interaction, and structure of the SD, which is an active site of intracellular signaling necessary for podocyte function. Nephrin is a principal component of the glomerular slit diaphragm (SD), a highly specialized intercellular junction that constitutes the ultrafiltration barrier of the kidney.1 Structurally, nephrin is a type-1 transmembrane glycoprotein with 10 predicted asparagine-(N)-linked glycosylation sites located on its ectodomain.2 Recently, the sites of these N-linked glycans on the ectodomain of nephrin were mapped by mass spectrometry; and their terminal sugar residues were identified by the use of carbohydrate-specific lectins, which study showed that human nephrin is a sialoprotein with terminal sugars of high mannose glycans and galactose. 3 We have also shown that N-linked glycosylation is absolutely critical for the biosynthesis of the newly synthesized nephrin molecules in the endoplasmic reticulum (ER) and for their proper transport to the plasma membrane. 4 Moreover, we recently demonstrated that N-linked glycosylation of nephrin in the ER is highly dependent on the orchestration by calreticulin as a lectin chaperone and the levels of intracellular ATP as an energy source. 5,6

Downregulation of the antioxidant protein peroxiredoxin 2 contributes to angiotensin II–mediated podocyte apoptosis

“…38 Galectin-1 (Gal-1), a newly described slit diaphragm protein, triggers increased tyrosine phosphorylation of nephrin, which activates Erk 1/2. 39 In contrast, Neph1 has been shown to negatively regulate Erk 1/2 signaling in podocytes. 40 Although the role of these kinases in glomerular diseases is not fully understood, it has been suggested in a diabetic mouse model that failure to phosphorylate Akt causes podocyte apoptosis.…”

Kidney Response to Heart Failure: Proteomic Analysis of Cardiorenal Syndrome

“…Mechanisms how HF itself can induce albuminuria are incompletely understood, but elevated renal venous pressure [45], ANG-II-induced changes in renal hemodynamics [46] or alterations in glomerular electrostatic barrier function [47] were implicated. The list of proteins upregulated in HF kidney contained several proteins that take part in glomerular filtration barrier, such as tight junction protein 1 (ZO-1), galectin-1 [48], basal cell adhesion molecule (BCAM) and chloride intracellular channel protein 5 (CLIC5) [49]. We can hypothesize that upregulation of these proteins in ACF HF kidney may reflect compensatory response to glomerular filtration barrier damage, indicating that proteinuria in HF is not only due to hemodynamic changes, but also due to altered filtration barrier [47].…”

mTORC1 activation triggers the unfolded protein response in podocytes and leads to nephrotic syndrome

“…21 The band that corresponded to a density of approximately 60 kDa (albumin) was measured using NIH Image ver.1.63, and the urinary albumin to urinary creatinine excretion ratio was calculated based on measurements from the Jaffe assay.…”