In vivo antibody-mediated modulation of aminopeptidase A in mouse proximal tubular epithelial cells

The anti-PLA2R antibody in membranous nephropathy: what we know and what remains a decade after its discovery

The discovery in 2009 of the M-type phospholipase A2 receptor (PLA2R) as the primary target in membranous nephropathy (MN) greatly advanced basic and clinical research. Primary MN is now considered a renal-limited autoimmune disease, with antibodies against PLA2R (aPLA2Rab) identified in 70-80 % of patients of various ethnic groups. Although the use of aPLA2Rab as a diagnostic and prognostic biomarker is now widely accepted, many questions related to the development of the auto-immune response, the role of IgG subclasses and antigenic epitopes, and the pathways to podocyte injury remain unresolved. PLA2R-associated MN most likely develops governed by factors such as genetic susceptibility, loss of tolerance, alterations in antigen expression with a role for environmental factors like air pollution, smoking, and infections. More detailed knowledge of genetic factors, the relevant B- and T-cell epitopes, and the mechanisms of podocyte injury is needed to identify patients at risk for disease progression and to develop optimized, targeted treatment strategies. In this review we highlight unresolved issues, addressing initiation of antibody formation, the timeline of antibody production, the role of IgG subclass, and the pathogenicity of the antibodies in concert with complement to produce glomerular pathology and proteinuria.

Nanoparticle transport in epithelial cells: pathway switching through bioconjugation

The understanding and control of nanoparticle transport into and through cellular compartments is central to biomedical applications of nanotechnology. Here, it is shown that the transport pathway of 50 nm polystyrene nanoparticles decorated with vitamin B12 in epithelial cells is different compared to both soluble B12 ligand and unmodified nanoparticles, and this is not attributable to B12 recognition alone. Importantly, the study indicates that vitamin B12 -conjugated nanoparticles circumnavigate the lysosomal compartment, the destination of soluble vitamin B12 ligand. Whereas cellular trafficking of soluble B12 is confirmed to occur via the clathrin-mediated pathway, transport of B12 -conjugated nanoparticles appears to predominantly take place by a route that is perturbed by caveolae-specific inhibitors. This data suggests that, following its conjugation to nanoparticles, in addition to dramatically increasing the cellular uptake of nanoparticles, the normal cell trafficking of B12 is switched to an alternative pathway, omitting the lysosomal stage: a result with important implications for oral delivery of nanoparticulate diagnostics and therapeutics.

Albuminuria in mice after injection of antibodies against aminopeptidase A: role of angiotensin II

It has been shown that injection of combinations of anti-aminopeptidase A (APA) monoclonal antibodies (mAb) that inhibit the enzyme activity induces an acute albuminuria in mice. This albuminuria is not dependent on inflammatory cells, complement, or the coagulation system. APA is an important regulator of the renin-angiotensin system because it is involved in the degradation of angiotensin II (Ang II). This study examined the potential role of glomerular Ang II in the induction of albuminuria. The relation among renal Ang II, glomerular APAX enzyme activity, and albuminuria was examined first. Injection of the nephritogenic combinations ASD-3/37 and ASD-37/41 in BALB/c mice induced albuminuria, whereas the non-nephritogenic combination ASD-3/41 had no effect. There was no clear relation between the inhibition of glomerular APA activity and albuminuria, yet it was evident that intrarenal Ang II levels were significantly increased in albuminuric mice and not in nonalbuminuric mice. As a next step, anti-APA mAb were administered to angiotensinogen-deficient mice that do not produce Ang II, and kidney morphology and albuminuria were determined. Angiotensinogen-deficient mice also developed albuminuria upon ASD-37/41 administration. Altogether, these findings clearly demonstrate that Ang II is not required for the induction of albuminuria upon injection of enzyme-inhibiting anti-APA mAb.