Proliferation Signal Inhibitor associated proteinuria in a renal transplant recipient: Dysfunction of proximal tubular epithelial cells is a result of decreased cubilinand/or megalin expression? : Proliferation Signal Inhibitor associated Proteinuria

Abstract: Background The proliferation signal inhibitors (PSIs) sirolimus (SRL) and everolimus (ERL) are the potent immunosuppressive drugs using in organ transplantation and has been used successfully in renal transplant recipients (RTX) as well. PSIs are the key factors to overcome the allograft rejections after successful organ transplantation since the immune system starts to react against the graft. SRL and ERL prevents the action of immune system b inhibits the proliferation of T- and B-cells by inhibiting the intracellular signaling of interleukin-2. The presence of excess amount of serum proteins including albumin in the urine is considered as proteinuria, which reflects the loss of kidney function. The occurrence of proteinuria can be the result of abnormal glomerular filtration and/or impaired tubular endocytic function of renal proximal tubular epithelial cells (PTECs). Megalin and cubulin are two scavenger receptors present on epical surface of PTECs and involved in reabsorption of proteins after glomerular ultrafiltration process in the kidney. Proteinuria appears too high in renal transplanted patients during ongoing   treatment with PSIs. Aim Our study aimed to investigate and correlate the expression level of megalin and cubilin and albumin uptake in PTEC of renal transplanted patients before and after conversion to PSI. Methods To retrieve the maximal expression of our interest molecules in renal PTECs, we optimized antigen retrieval (AR) method and primary antibody dilution for each molecule separately. An optimization experiment was performed on 3 different normal patients renal biopsies were used. Later, human renal biopsy specimens originated from 4 different renal transplanted patients were used in this study. From all the 4 patients biopsy specimens were taken before and ongoing administration of PSIs (SRL, ERL). The expression of megalin, cubilin and albumin uptake in PTEC of renal transplant patients was determined by immunohistochemical staining. Results Based on the optimization experiments, we selected the AR method and primary antibody dilution for the expression of megalin, cubilin and albumin uptake. In 4 renal transplanted patients following administration of PSIs results in patients 1, 2, 3 expression of megalin, cubilin and albumin uptake during ongoing PSI treatment was not comparable or even more intense than before PSIs introduction. The expression of megalin, cubilin and albumin uptake was reduced in patient 4 during ongoing PSI treatment. Conclusion Our findings suggest that the renal transplant patient 4 developed proteinuria during PSI medication. The expression of megalin, cubilin and albumin uptake was markedly decreased during ongoing PSI treatment in patient 4. We concluded that there is a direct link between PSI medication and tubular dysfunction, which might cause proteinuria