sirolimus and Nephrosis--Lipoid

Amelioration of podocyte injury, which can lead to podocyte detachment, is the target of therapeutic intervention in glomerular diseases. Since podocytes are terminally differentiated cells with little or no proliferative ability, their loss results in permanent glomerular dysfunction. In immune-mediated glomerular diseases, a variety of immunomodulatory agents are used to maintain podocytes by systemic immunosuppression, which indirectly ameliorates podocyte injury by interrupting the input of immunological stress. However, in contrast to the indirect therapeutic strategy mediated by immunosuppression, recent data now suggest that immunomodulatory agents directly act on podocytes in an agent-dependent manner. Indeed, the therapeutic efficacy of immunomodulatory agents is, at least in part, derived by the direct action on podocytes. In this review, we discuss the molecular targets and mechanisms by which immunomodulatory agents alleviate podocyte injury and examine their clinical significance.

Topics: Abatacept; Adjuvants, Immunologic; Calcineurin Inhibitors; Everolimus; Glomerulonephritis; Glomerulonephritis, Membranous; Glomerulosclerosis, Focal Segmental; Glucocorticoids; Humans; Immunologic Factors; Immunosuppressive Agents; Levamisole; Mycophenolic Acid; Nephrosis, Lipoid; Nephrotic Syndrome; Podocytes; Ribonucleosides; Rituximab; Sirolimus; Tacrolimus; TOR Serine-Threonine Kinases

Chronic glomerular diseases, associated with renal failure and cardiovascular morbidity, represent a major health issue. However, they remain poorly understood. Here we have reported that tightly controlled mTOR activity was crucial to maintaining glomerular podocyte function, while dysregulation of mTOR facilitated glomerular diseases. Genetic deletion of mTOR complex 1 (mTORC1) in mouse podocytes induced proteinuria and progressive glomerulosclerosis. Furthermore, simultaneous deletion of both mTORC1 and mTORC2 from mouse podocytes aggravated the glomerular lesions, revealing the importance of both mTOR complexes for podocyte homeostasis. In contrast, increased mTOR activity accompanied human diabetic nephropathy, characterized by early glomerular hypertrophy and hyperfiltration. Curtailing mTORC1 signaling in mice by genetically reducing mTORC1 copy number in podocytes prevented glomerulosclerosis and significantly ameliorated the progression of glomerular disease in diabetic nephropathy. These results demonstrate the requirement for tightly balanced mTOR activity in podocyte homeostasis and suggest that mTOR inhibition can protect podocytes and prevent progressive diabetic nephropathy.

Topics: Adaptor Proteins, Signal Transducing; Adult; Animals; Carrier Proteins; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Disease Progression; Gene Dosage; Genetic Predisposition to Disease; Humans; Kidney Glomerulus; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Mice, Knockout; Mice, Transgenic; Multiprotein Complexes; Nephrosis, Lipoid; Podocytes; Proteins; Proteinuria; Rapamycin-Insensitive Companion of mTOR Protein; Regulatory-Associated Protein of mTOR; Sirolimus; TOR Serine-Threonine Kinases; Trans-Activators; Transcription Factors

Although podocyte damage is known to be responsible for the development of minimal-change disease (MCD), the underlying mechanism remains to be elucidated. Previously, using a rat MCD model, we showed that endoplasmic reticulum (ER) stress in the podocytes was associated with the heavy proteinuric state and another group reported that a mammalian target of rapamycin complex 1 (mTORC1) inhibitor protected against proteinuria. In this study, which utilized a rat MCD model, a combination of immunohistochemistry, dual immunofluorescence and confocal microscopy, western blot analysis, and quantitative real-time RT-PCR revealed co-activation of the unfolded protein response (UPR), which was induced by ER stress, and mTORC1 in glomerular podocytes before the onset of proteinuria and downregulation of nephrin at the post-translational level at the onset of proteinuria. Podocyte culture experiments revealed that mTORC1 activation preceded the UPR that was associated with a marked decrease in the energy charge. The mTORC1 inhibitor everolimus completely inhibited proteinuria through a reduction in both mTORC1 and UPR activity and preserved nephrin expression in the glomerular podocytes. In conclusion, mTORC1 activation may perturb the regulatory system of energy metabolism primarily by promoting energy consumption and inducing the UPR, which underlie proteinuria in MCD.

Topics: Animals; Blotting, Western; Cells, Cultured; Endoplasmic Reticulum Stress; Everolimus; Fluorescent Antibody Technique; Immunohistochemistry; Microscopy, Confocal; Nephrosis, Lipoid; Podocytes; Rats; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; Sirolimus; Statistics, Nonparametric; TOR Serine-Threonine Kinases; Unfolded Protein Response

In clinical renal transplantation, an increase in proteinuria after conversion from calcineurin inhibitors to rapamycin has been reported. In contrast, there are studies showing a nephro-protective effect of rapamycin in proteinuric diseases characterized by progressive interstitial inflammatory fibrosis.. Because of the contradictory reports concerning rapamycin on proteinuria, we examined proteinuria and podocyte damage markers on two renal disease models, with clearly different pathophysiological mechanisms: a glomerular toxico-immunological model induced by puromycin aminonucleoside, and a chronic hyperfiltration and inflammatory model by mass reduction, both treated with a fixed high rapamycin dose.. In puromycin groups, rapamycin provoked significant increases in proteinuria, together with a significant fall in podocin immunofluorescence, as well as clear additional damage to podocyte foot processes. Conversely, after mass reduction, rapamycin produced lower levels of proteinuria and amelioration of inflammatory and pro-fibrotic damage. In contrast to the puromycin model, higher glomerular podocin and nephrin expression and amelioration of glomerular ultrastructural damage were found.. We conclude that rapamycin has dual opposing effects on subjacent renal lesion, with proteinuria and podocyte damage aggravation in the glomerular model and a nephro-protective effect in the chronic inflammatory tubulointerstitial model. Rapamycin produces slight alterations in podocyte structure when acting on healthy podocytes, but it clearly worsens those podocytes damaged by other concomitant injury.

Topics: Animals; Disease Models, Animal; Immunosuppressive Agents; Male; Nephrosis, Lipoid; Podocytes; Proteinuria; Rats; Rats, Sprague-Dawley; Sirolimus

Topics: Adult; Drug Therapy, Combination; Female; Humans; Immunosuppressive Agents; Kidney; Nephrosis, Lipoid; Sirolimus; Tacrolimus