Minimal change disease and treatment with steroids 7/24/2007 Zae Kim, MD

Clinical Question Why does MCD respond to steroid? Why do they develop resistance?

Introduction Most common cause of the nephrotic syndrome in children ~10-15% of nephrotic syndrome in adults, third most common after MN and FSGS –More common in Hispanics, Asians, Arabs and Caucasians clinical and pathological entity defined by selective proteinuria and hypoalbuminemia that occurs in the absence of –cellular glomerular infiltrates or –immunoglobulin deposits

Light microscopy of glomerulus in MCD

Immunofluorescence Microscopy

Electron Microscopy

The glomerular capillary wall Van den Berg, Weening, Clinical Science (2004) 107, 125–136 Normal MCD

What is the Pathogenesis?

Pathogenesis - “Intrinsic factor” Genetic basis for hereditary NS NS of the Finnish type Autosomal-recessive steroid-resistant NS Familial forms of FSGS Diffuse mesangila sclerosis associated with Denys-Drash syndrome and with Frasier syndrome NS associated with nail-patella syndrome –Help elucidate molecular aspect of FSGS –Not clear for MCD

Molecular anatomy of the podocyte foot process cytoskeleton Nature Genetics 24, (2000)

Pathogenesis – extrinsic factor, better explanation for MCD Clinical Observations - Shalhoub’s hypothesis –MCD frequently remits with measles infection –Corticosteroids and alkylating drugs cause a remission –Association of MCD with Hodgkin disease Experimental Observations –T cell hybridoma (Koyama KI 1991 (40): ) –Removal of glomerular permeability factor leads to normal kidney (Ali Transplantation 1994 Oct 15;58(7):849-52) “circulating factor” –possible link between T-cell response and glomerular disease

How does steroid work in MCD? Widely used in treatment but their mode of action is poorly understood What is its effectiveness in MCD where there is no evident inflammation

Steroid – quick overview Inhibitory effects on both innate and acquired immunologic function Innate Immune function –Reduced Inflammatory response: inhibit transmigration of leukocytes attenuate the generation of inflammatory exudates –Phospholipase A2 suppresion –COX-2 suppression Acquired Immune function –Antigen presenting cells, B cell and T cells

Overview of Intracellular Effects

Could steroid have more direct effect in kidney?

Direct effects of dexamethasone on human podocyte – Xing, Saleem, et al Hypothesis: –Glucocorticoid exert direct protection of podocytes from injury and/or promotion of repair Nephrin: podocyte specific protein –mutation of NPHS2 gene - cause congenital nephrotic syndrome of Finnish type –Studies show possible downregulation of nephrin in MCD

Result – effects of dexamethasone on podocyte maturation at 37 C and expression of nephrin Quantificaton of nephrin Immunofluorescent staining

Summary Dexamethasone enhanced and accelerated podocyte maturation, with a particulary striking effect on expression of nephrin

Other steroid response In disease stateWith dexamethasone p21Upregulateddownregulation allow podocyte to enter the cell cycle – enhance ability to repair VEGFa mitogen for vascular endotheila cells Downregulated p52Induces apoptosisdownregulated

Overexpression of Interleukin-13 Induces Minimal-Change– Like Nephropathy in Rats Background –MCD may be a T cell dependent disorder that results in glomerular podocyte dysfunction –Th2 cytokine bias in patients with MCD MCD associated with atopy and allergy Relapse MCD with elevated IL-4 and IL-13 –Association between MCD and Hodgkins’s disease IL-13 known to be an autocrine growth factor for the Reed- Sternberg

Hypothesis IL-13 may play an important role in the development of proteinuria in MCNS by exerting a direct effect on podocytes, acting through the IL-13 receptors on the podocyte cell surface, initiating certain signaling pathways that eventually lead to changes in the expression of podocyte-related proteins (nephrin, podocin, and dystroglycan) IL-13 transfected mouse was used as a model

Mean 24-h urine albumin excretion (mg/24 h)

Comparison of control, IL-13-transfected mouse at experiment end (day 70) ParameterControl Rats (n=17) Group 1 (proteinuric rats), n=34 Grp 2: neprhrotic rats n=7 Serum albumin42.7 +/ / /- 2.2 Urine albumin0.36 +/ / / Serum cholesterol1.72 +/ / / Serum IL / / / Nephrin0.16 +/ / / Podocin0.25+/ / / Yellow = p <0.001 vs controlRed = p<0.001 vs control and Grp 1

Histopathologic features on day 70 at killing (A) Glomerulus of IL-13–transfected rat showing no significant histologic changes (periodic acid-Schiff stain). (B) Glomerulus of IL-13–transfected rat showing fusion of podocyte foot processes (arrows). (C) Glomerulus of control rat showing normal individual podocyte foot processes along the glomerular basement membrane (GBM; arrows).

Immunofluorescence staining of glomeruli for protein expression of nephrin, podocin, dystroglycan, and synaptopodin nephrin podocin dystroglycan synaptopodin Control IL-13 infected

Summary IL-13-transfected rats –Developed minimal change like GN, as evidence by LM and EM changes –decrease in the expression of nephrin, podocin, and dystroglycan associated with increased urinary albumin excretion and podocyte foot process effacement suggesting that these proteins are essential in maintaining the filtration barrier, thus controlling glomerular permeability decrease was not due to loss of podocytes -

What does it all mean… There is more to steroid than I knew… “circulating factor” –Prognostic indicator? Why are some MCDs steroid responsive while others are resistant?

The end