Increased expression of mineralocorticoid effector mechanisms in kidney biopsies of patients with heavy proteinuria.
BACKGROUND: Aldosterone has emerged as a deleterious hormone in the heart, with mineralocorticoid receptor (MR) blockade reducing mortality in patients with severe heart failure. There is also experimental evidence that aldosterone contributes to the development of nephrosclerosis and renal fibrosis in rodent models, but little is known of its role in clinical renal disease. METHODS AND RESULTS: We quantified MR, serum- and glucocorticoid-regulated kinase 1 (sgk1), and mRNA expression of inflammatory mediators such as macrophage chemoattractant protein-1 (MCP-1), transforming growth factor-beta1, and interleukin-6 in 95 human kidney biopsies in patients with renal failure and mild to marked proteinuria of diverse etiologic origins. We measured renal function, serum aldosterone, urinary MCP-1 protein excretion, and the amount of chronic renal damage. Macrophage invasion was quantified by CD68 and vascularization by CD34 immunostaining. Serum aldosterone correlated negatively with creatinine clearance (P<0.01) and positively with renal scarring (P<0.05) but did not correlate with MR mRNA expression or proteinuria. Patients with heavy albuminuria (>2 g/24 h; n=15) had the most renal scarring and the lowest endothelial CD34 staining. This group showed a significant 5-fold increase in MR, a 2.5-fold increase in sgk1 expression and a significant increase in inflammatory mediators (7-fold increase in MCP-1, 3-fold increase in transforming growth factor-beta1, and 2-fold increase in interleukin-6 mRNA). Urinary MCP-1 protein excretion and renal macrophage invasion were significantly increased in patients with heavy albuminuria. CONCLUSIONS: These studies support animal data linking aldosterone/MR activation to renal inflammation and proteinuria. Further studies are urgently required to assess the potential beneficial effects of MR antagonism in patients with renal disease. (+info)
Nephrotic syndrome and aberrant expression of laminin isoforms in glomerular basement membranes for an infant with Herlitz junctional epidermolysis bullosa.
Herlitz junctional epidermolysis bullosa (H-JEB) is a hereditary bullous disease caused by absent expression of laminin-5, a component of anchoring filaments within the dermal-epidermal basement membrane zone. Affected individuals usually die during the first 1 year of life. We studied an infant with H-JEB who presented with nephrotic syndrome, a previously unreported complication that may contribute to early death in this disease. DNA analysis revealed a compound heterozygote for mutations 2379delG and Q995X in the LAMB3 gene. The patient had massive albuminuria, attributable to failure of the glomerular filtration barrier, and high urinary N-acetylglucosaminidase levels, indicating renal tubular involvement. Electron-microscopic examination of the renal tissue revealed diffuse fusion of the foot processes, irregular swelling of the lamina rara interna, and disappearance of endothelial cell fenestrations. Immunohistopathologic analysis of the patient's renal tissue revealed compositional changes in laminin isoforms of the glomerular basement membrane and no detectable laminin-5 in the renal tubular basement membrane, which suggests that laminin-5 may play an important role in renal function. Our findings strongly suggest that H-JEB should be considered in the spectrum of congenital nephrotic syndromes. Combination therapy with meticulous skin care and treatment strategies established for congenital nephrotic syndromes may rescue patients with this disease. (+info)
Olfactory bulb external tufted cells are synchronized by multiple intraglomerular mechanisms.
In rat olfactory bulb slices, external tufted (ET) cells spontaneously generate spike bursts. Only ET cells affiliated with the same glomerulus exhibit significant synchronous activity, suggesting that synchrony results mainly from intraglomerular interactions. The intraglomerular mechanisms underlying their synchrony are unknown. Using dual extracellular and patch-clamp recordings from ET cell pairs of the same glomerulus, we found that the bursting of ET cells is synchronized by several mechanisms. First, ET cell pairs of the same glomerulus receive spontaneous synchronous fast excitatory synaptic input that can also be evoked by olfactory nerve stimulation. Second, they exhibit correlated spontaneous slow excitatory synaptic currents that can also be evoked by stimulation of the external plexiform layer. These slow currents may reflect the repetitive release of glutamate via spillover from the dendritic tufts of other ET or mitral/tufted cells affiliated with the same glomerulus. Third, ET cells exhibit correlated bursts of inhibitory synaptic activity immediately after the synchronous fast excitatory input. These bursts of IPSCs were eliminated by CNQX and may therefore reflect correlated feedback inhibition from periglomerular cells that are driven by ET cell spike bursts. Fourth, in the presence of fast synaptic blockers, ET cell pairs exhibit synchronous slow membrane current oscillations associated with rhythmic spikelets, which were sensitive to the gap junction blocker carbenoxolone. These findings suggest that coordinated synaptic transmission and gap junction coupling synchronize the spontaneous bursting of ET cells of the same glomerulus. (+info)
Dominant mutations of Col4a1 result in basement membrane defects which lead to anterior segment dysgenesis and glomerulopathy.
Members of the type IV collagen family are essential components of all basement membranes (BMs) and define structural stability as well as tissue-specific functions. The major isoform, alpha1.alpha1.alpha2(IV), contributes to the formation of many BMs and its deficiency causes embryonic lethality in mouse. We have identified an allelic series of three ENU induced dominant mouse mutants with missense mutations in the gene Col4a1 encoding the alpha1(IV) subunit chain. Two severe alleles (Bru and Svc) have mutations affecting the conserved glycine residues in the Gly-Xaa-Yaa collagen repeat. Bru heterozygous mice display defects similar to Axenfeld-Rieger anomaly, including iris defects, corneal opacity, vacuolar cataracts, significant iris/corneal adhesions, buphthalmos and optic nerve cupping, a sign indicative of glaucoma. Kidneys of Bru mice have peripheral glomerulopathy characterized by hypertrophy and hyperplasia of the parietal epithelium of Bowman's capsule. A milder allele (Raw) contains a mutation in the Yaa residue of the collagen repeat and was identified by a silvery appearance of the retinal arterioles. All phenotypes are associated with BM defects that affect the eye, kidney and other tissues. This allelic series shows that mutations affecting the collagen domain cause dominant negative effects on the expression and function of the major collagen IV isoform alpha1(IV), and pathological effects vary with the individual mutations. (+info)
Innate stimuli accentuate end-organ damage by nephrotoxic antibodies via Fc receptor and TLR stimulation and IL-1/TNF-alpha production.
Innate stimuli are well recognized as adjuvants of the systemic immune response. However, their role in driving end-organ disease is less well understood. Whereas the passive transfer of glomerular-targeting Abs alone elicited minimal renal disease, the concomitant delivery of innate stimuli triggered severe nephritis, characterized by proliferative glomerulonephritis with crescent formation, and tubulointerstitial disease. Specifically, stimulating TLR2, TLR3, TLR4, and TLR5 by using peptidoglycan, poly(I:C), LPS, and flagellin, respectively, all could facilitate anti-glomerular Ab-elicited nephritis. In this model, innate and immune triggers synergistically activated several cytokines and chemokines, including IL-1, IL-6, TNF-alpha, and MCP-1, some of which were demonstrated to be absolutely essential for the development of renal disease. Genetic studies revealed that, whereas the innate trigger is dependent on TLR/IL-1R-associated kinase-mediated signaling, the immune component was contingent on FcR-mediated signals. Importantly, infiltrating leukocytes as well as intrinsic glomerular cells may both serve to integrate these diverse signals. Extrapolating to spontaneous immune-mediated nephritis, although the adaptive immune system may be important in generating end-organ targeting Abs, the extent of damage inflicted by these Abs may be heavily dependent on cues from the innate immune system. (+info)
Transgenic isolation of skeletal muscle and kidney defects in laminin beta2 mutant mice: implications for Pierson syndrome.
Pierson syndrome is a recently defined disease usually lethal within the first postnatal months and caused by mutations in the gene encoding laminin beta2 (LAMB2). The hallmarks of Pierson syndrome are congenital nephrotic syndrome accompanied by ocular abnormalities, including microcoria (small pupils), with muscular and neurological developmental defects also present. Lamb2(-/-) mice are a model for Pierson syndrome; they exhibit defects in the kidney glomerular barrier, in the development and organization of the neuromuscular junction, and in the retina. Lamb2(-/-) mice fail to thrive and die very small at 3 weeks of age, but to what extent the kidney and neuromuscular defects each contribute to this severe phenotype has been obscure, though highly relevant to understanding Pierson syndrome. To investigate this, we generated transgenic mouse lines expressing rat laminin beta2 either in muscle or in glomerular epithelial cells (podocytes) and crossed them onto the Lamb2(-/-) background. Rat beta2 was confined in skeletal muscle to synapses and myotendinous junctions, and in kidney to the glomerular basement membrane. In transgenic Lamb2(-/-) mice, beta2 deposition in only glomeruli prevented proteinuria but did not ameliorate the severe phenotype. By contrast, beta2 expression in only muscle restored synaptic architecture and led to greatly improved health, but the mice died from kidney disease at 1 month. Rescue of both glomeruli and synapses was associated with normal weight gain, fertility and lifespan. We conclude that muscle defects in Lamb2(-/-) mice are responsible for the severe failure to thrive phenotype, and that renal replacement therapy alone will be an inadequate treatment for Pierson syndrome. (+info)
BACKGROUND: Glomerular basement membrane (GBM), a key component of the blood-filtration apparatus in the in the kidney, is formed through assembly of type IV collagen with laminins, nidogen, and sulfated proteoglycans. Mutations or deletions involving alpha3(IV), alpha4(IV), or alpha5(IV) chains of type IV collagen in the GBM have been identified as the cause for Alport syndrome in humans, a progressive hereditary kidney disease associated with deafness. The pathological mechanisms by which such mutations lead to eventual kidney failure are not completely understood. METHODS AND FINDINGS: We showed that increased susceptibility of defective human Alport GBM to proteolytic degradation is mediated by three different matrix metalloproteinases (MMPs)--MMP-2, MMP-3, and MMP-9--which influence the progression of renal dysfunction in alpha3(IV)-/- mice, a model for human Alport syndrome. Genetic ablation of either MMP-2 or MMP-9, or both MMP-2 and MMP-9, led to compensatory up-regulation of other MMPs in the kidney glomerulus. Pharmacological ablation of enzymatic activity associated with multiple GBM-degrading MMPs, before the onset of proteinuria or GBM structural defects in the alpha3(IV)-/- mice, led to significant attenuation in disease progression associated with delayed proteinuria and marked extension in survival. In contrast, inhibition of MMPs after induction of proteinuria led to acceleration of disease associated with extensive interstitial fibrosis and early death of alpha3(IV)-/- mice. CONCLUSIONS: These results suggest that preserving GBM/extracellular matrix integrity before the onset of proteinuria leads to significant disease protection, but if this window of opportunity is lost, MMP-inhibition at the later stages of Alport disease leads to accelerated glomerular and interstitial fibrosis. Our findings identify a crucial dual role for MMPs in the progression of Alport disease in alpha3(IV)-/- mice, with an early pathogenic function and a later protective action. Hence, we propose possible use of MMP-inhibitors as disease-preventive drugs for patients with Alport syndrome with identified genetic defects, before the onset of proteinuria. (+info)
Pathology and protection in nephrotoxic nephritis is determined by selective engagement of specific Fc receptors.
Introduction of heterologous anti-glomerular basement membrane antiserum (nephrotoxic serum, NTS) into presensitized mice triggers the production of IgG anti-NTS antibodies that are predominantly IgG2b and the glomerular deposition of pathogenic immune complexes, leading to accelerated renal disease. The pathology observed in this model is determined by the effector cell activation threshold that is established by the coexpression on infiltrating macrophages of the IgG2a/2b restricted activation receptor FcgammaRIV and its inhibitory receptor counterpart, FcgammaRIIB. Blocking FcgammaRIV with a specific monoclonal antibody thereby preventing IgG2b engagement or treatment with high dose intravenous gamma-globulin (IVIG) to down-regulate FcgammaRIV while up-regulating FcgammaRIIB, protects mice from fatal disease. In the absence of FcgammaRIIB, IVIG is not protective; this indicates that reduced FcgammaRIV expression alone is insufficient to protect animals from pathogenic IgG2b immune complexes. These results establish the significance of specific IgG subclasses and their cognate FcgammaRs in renal disease. (+info)