Kidney transplant recipients (KTRs) are extremely vulnerable to SARS‐CoV‐2 infection and show an impaired immune response to SARS‐CoV‐2 vaccination. We analyzed factors related to vaccination efficiency in KTRs. In a multicenter prospective observational study (NCT04743947), IgG antibodies levels against SARS‐CoV‐2 spike S1 subunit and their neutralization capacity after SARS‐CoV‐2 vaccination were analyzed in 225 KTRs and compared to 176 controls. After the vaccination, 56 (24.9%) KTRs became seropositive of whom 68% had neutralizing antibodies. This immune response was significantly lower compared to controls (239 [78–519] BAU/ml versus 1826 [560–3180] BAU/ml for KTRs and controls, p < .0001). The strongest predictor for an impaired response was mycophenolate mofetil (MMF) treatment. Multivariate regression analysis revealed that MMF‐free regimen was highly associated with seroconversion (OR 13.25, 95% CI 3.22–54.6; p < .001). In contrast, other immunosuppressive drugs had no significant influence. 187 out of 225 KTRs were treated with MMF of whom 26 (13.9%) developed antibodies. 23 of these seropositive KTRs had a daily MMF dose ≤1 g. Furthermore, higher trough MMF concentrations correlated with lower antibody titers (R −0.354, p < .001) supporting a dose‐dependent unfavorable effect of MMF. Our data indicate that MMF dose modification could lead to an improved immune response.

Nephrin, the key molecule of the glomerular slit diaphragm, is expressed on the surface of podocytes and is critical in preventing albuminuria. In diabetes, hyperglycemia leads to the loss of surface expression of nephrin and causes albuminuria. Here, we report a mechanism that can explain this phenomenon: hyperglycemia directly enhances the rate of nephrin endocytosis via regulation of the ␤-arrestin2-nephrin interaction by PKC␣. We identified PKC␣ and protein interacting with c kinase-1 (PICK1) as nephrin-binding proteins. Hyperglycemia induced up-regulation of PKC␣ and led to the formation of a complex of nephrin, PKC␣, PICK1, and ␤-arrestin2 in vitro and in vivo. Binding of ␤-arrestin2 to the nephrin intracellular domain depended on phosphorylation of nephrin threonine residues 1120 and 1125 by PKC␣. Further, cellular knockdown of PKC␣ and/or PICK1 attenuated the nephrin-␤-arrestin2 interaction and abrogated the amplifying effect of high blood glucose on nephrin endocytosis. In C57BL/6 mice, hyperglycemia over 24 h caused a significant increase in urinary albumin excretion, supporting the concept of the rapid impact of hyperglycemia on glomerular permselectivity. In summary, we have provided a molecular model of hyperglycemia-induced nephrin endocytosis and subsequent proteinuria and highlighted PKC␣ and PICK1 as promising therapeutic targets for diabetic nephropathy.Diabetes mellitus is a major health problem in Western countries. Despite therapeutic advances, diabetic nephropathy remains the leading cause of end stage renal disease (1). Chronic hyperglycemia causes glomerular damages such as endothelial dysfunction, loss of negative charges in the basement membrane, and podocyte damage (2). Microalbuminuria is an early symptom of a "leaky" glomerular barrier and is associated with a markedly increased cardiovascular risk (3).Podocytes are visceral epithelial cells wrapped around glomerular capillaries and are connected by the slit diaphragm. This specialized cell junction is a dynamic multiprotein complex that functions as a size-selective sieve to prevent the loss of plasma proteins through urine (4, 5). Nephrin serves as the backbone of this diaphragm by functioning as a regulator of podocyte signaling and mediator of actin dynamics (6 -8). Several podocyte signaling abnormalities have been noted in diabetes. For example, mice and humans with diabetes show altered distribution and expression of nephrin (9 -11), and hyperglycemia increases diacylglycerol generation, causing PKC activation (2). However, it is not fully understood how "hyperglycemic" signaling in diabetes affects the expression and distribution of nephrin.Menne et al. (12) reported a major step elucidating podocyte signaling in diabetes: they showed that albuminuria does not develop in diabetic PKC␣-deficient mice and concluded that decreased nephrin expression in diabetes is a result of altered transcriptional regulation. All of the studies until now were conducted in chronic models of diabetes (13). Therefore, their conclusions were based...

Cardiovascular and renal pathologies are frequently associated with an activated renin-angiotensin-system (RAS) and increased levels of its main effector and vasoconstrictor hormone angiotensin II (Ang II). Angiotensin-converting-enzyme-2 (ACE2) has been described as a crucial enzymatic player in shifting the RAS towards its so-called alternative vasodilative and reno-protective axis by enzymatically converting Ang II to angiotensin-(1-7) (Ang-(1-7)). Yet, the relative contribution of ACE2 to Ang-(1-7) formation in vivo has not been elucidated. Mass spectrometry based quantification of angiotensin metabolites in the kidney and plasma of ACE2 KO mice surprisingly revealed an increase in Ang-(1-7), suggesting additional pathways to be responsible for alternative RAS activation in vivo. Following assessment of angiotensin metabolism in kidney homogenates, we identified neprilysin (NEP) to be a major source of renal Ang-(1-7) in mice and humans. These findings were supported by MALDI imaging, showing NEP mediated Ang-(1-7) formation in whole kidney cryo-sections in mice. Finally, pharmacologic inhibition of NEP resulted in strongly decreased Ang-(1-7) levels in murine kidneys. This unexpected new role of NEP may have implications for the combination therapy with NEP-inhibitors and angiotensin-receptor-blockade, which has been shown being a promising therapeutic approach for heart failure therapy.