Intravital Imaging Reveals Angiotensin II–Induced Transcytosis of Albumin by Podocytes

Abstract

Albuminuria is a hallmark of kidney disease of various etiologies and usually caused by deterioration of glomerular filtration barrier integrity. We recently showed that angiotensin II (Ang II) acutely increases albumin filtration in the healthy kidney. Here, we used intravital microscopy to assess the effects of Ang II on podocyte function in rats. Acute infusion of 30, 60, or 80 ng/kg per minute Ang II enhanced the endocytosis of albumin by activation of the type 1 Ang II receptor and resulted in an average (6SEM) of 3.762.2, 72.3618.6 (P,0.001), and 239.4634.6 mm 3 (P,0.001) albumin-containing vesicles per glomerulus, respectively, compared with none at baseline or 10 ng/kg per minute Ang II. Immunostaining of Ang II-infused kidneys confirmed the presence of albumin-containing vesicles, which colocalized with megalin, in podocin-positive cells. Furthermore, podocyte endocytosis of albumin was markedly reduced in the presence of gentamicin, a competitive inhibitor of megalin-dependent endocytosis. Ang II infusion increased the concentration of albumin in the subpodocyte space, a potential source for endocytic protein uptake, and gentamicin further increased this concentration. Some endocytic vesicles were acidified and colocalized with LysoTracker. Most vesicles migrated from the capillary to the apical aspect of the podocyte and were eventually released into the urinary space. This transcytosis accounted for approximately 10% of total albumin filtration. In summary, the transcellular transport of proteins across the podocyte constitutes a new pathway of glomerular protein filtration. Ang II enhances the endocytosis and transcytosis of plasma albumin by podocytes, which may eventually impair podocyte function.

APOL1-G1 in Nephrocytes Induces Hypertrophy and Accelerates Cell Death

“…[47][48][49] Studies in rats showed that angiotensin II infusion increased albumin concentration in the subpodocyte space, possibly promoting endocytosis. 50 Moreover, excessive endocytosis of albumin by podocytes appears to be a factor underlying progressive renal injury. 47 It is thus tempting to speculate that APOL1 is involved in this process, and that the G1 risk variant may somehow impair adaptive processes by enhancing endocytic activity of podocytes under stress, precipitating cellular injury.…”

Arginine Vasopressin Promotes Redistribution of Adhesion Junction Protein E-Cadherin in Kidney Epithelial Cells

“…Transcytosis is a special type of receptor-mediated intracellular transport that has been reported in many cell types including neurons 30 and kidney. 31 In this type of intracellular transportation, proteins are captured in endocytozed vesicles (like what we observed in Fig. 4) and been transported across a cell Fig.…”

The Role of Renal Interstitial Cells in Proximal Tubular Regeneration

“…Consequently, tubular regeneration has been predominantly investigated in disease models of the tubular system, rather than during the aging of the healthy kidney. The use of serial intravital imaging, however, has markedly expanded our possibilities, thus allowing researchers to address structural and functional changes over prolonged periods of time in the same animal [12,51,52]. For example, the excitation laser used for multiphoton intravital microscopy can be employed as a tool to ablate single tubular cells via focused, high energy laser exposure in an otherwise healthy kidney.…”