Damodar Gullipalli

Combination of Factor H Mutation and Properdin Deficiency Causes Severe C3 Glomerulonephritis

Factor H (fH) and properdin both modulate complement; however, fH inhibits activation, and properdin promotes activation of the alternative pathway of complement. Mutations in fH associate with several human kidney diseases, but whether inhibiting properdin would be beneficial in these diseases is unknown. Here, we found that either genetic or pharmacological blockade of properdin, which we expected to be therapeutic, converted the mild C3 GN of an fH-mutant mouse to a lethal C3 GN with features of human dense deposit disease. We attributed this phenotypic change to a differential effect of properdin on the dynamics of alternative pathway complement activation in the fluid phase and the cell surface in the fH-mutant mice. Thus, in fH mutation-related C3 glomerulopathy, additional factors that impact the activation of the alternative pathway of complement critically determine the nature and severity of kidney pathology. These results show that therapeutic manipulation of the complement system requires rigorous disease-specific target validation.

Tissue-specific deletion of Crry from mouse proximal tubular epithelial cells increases susceptibility to renal ischemia–reperfusion injury

The murine cell surface protein Crry is a key complement regulator with similar activities to human membrane cofactor protein (MCP) and decay-accelerating factor. MCP plays a critical role in preventing complement-mediated tissue injury and its mutation has been implicated in several human kidney diseases. Study of Crry in mice has relevance to understanding MCP activity in human diseases but such efforts have been hampered by the embryonic lethality phenotype of Crry gene knockout. Here we used a conditional gene targeting approach and deleted Crry from the mouse proximal tubular epithelial cells where Crry is prominently expressed. Absence of Crry from proximal tubular epithelial cells resulted in spontaneous C3 deposition on the basolateral surface but no apparent renal disease in unchallenged mice. However, mice deficient in Crry on proximal tubular epithelial cells developed exacerbated renal injury when subjected to renal ischemia reperfusion showing increased blood urea nitrogen levels, higher tubular injury scores, more tubular epithelial cell apoptosis, and inflammatory infiltrates. Renal ischemia reperfusion injury in the Crry conditional knockout mice was prevented by blocking C3 and C5 activation using an anti-properdin or anti-C5 mAb, respectively. Thus, Crry has a critical role in protecting proximal tubular epithelial cells during ischemia reperfusion challenge. Our results highlight the latent risk for inflammatory kidney injury associated with defects in membrane complement regulators.

Properdin Contributes to Allergic Airway Inflammation through Local C3a Generation

Complement is implicated in asthma pathogenesis, but its mechanism of action in this disease remains incompletely understood. In this study, we investigated the role of properdin (P), a positive alternative pathway complement regulator, in allergen-induced airway inflammation. Allergen challenge stimulated P release into the airways of asthmatic patients, and P levels positively correlated with proinflammatory cytokines in human bronchoalveolar lavage (BAL). High levels of P were also detected in the BAL of OVA-sensitized and challenged but not naive mice. Compared with wild-type (WT) mice, P-deficient (P−/−) mice had markedly reduced total and eosinophil cell counts in BAL and significantly attenuated airway hyperresponsiveness to methacholine. Ab blocking of P at both sensitization and challenge phases or at challenge phase alone, but not at sensitization phase alone, reduced airway inflammation. Conversely, intranasal reconstitution of P to P−/− mice at the challenge phase restored airway inflammation to wild-type levels. Notably, C3a levels in the BAL of OVA-challenged P−/− mice were significantly lower than in wild-type mice, and intranasal coadministration of an anti-C3a mAb with P to P−/− mice prevented restoration of airway inflammation. These results show that P plays a key role in allergen-induced airway inflammation and represents a potential therapeutic target for human asthma.

C5 inhibition prevents renal failure in a mouse model of lethal C3 glomerulopathy

C3 glomerulopathy is a potentially life-threatening disease of the kidney caused by dysregulated alternative pathway complement activation. The specific complement mediator(s) responsible for kidney injury in C3 glomerulopathy are yet to be defined and no specific therapy is currently available. We previously developed a mouse model of lethal C3 glomerulopathy with factor H and properdin gene double mutations. Therefore, we used this model to examine the role of C5 and C5a receptor (C5aR) in the pathogenesis of the disease. Disease severity in these factor H/properdin double-mutant mice was found to be correlated with plasma C5 levels, and prophylactic anti-C5 mAb therapy was effective in preventing lethal C3 glomerulopathy. When given to these double-mutant mice that had already developed active disease with severe proteinuria, anti-C5 mAb treatment also prevented death in half of the mice. Deficiency of C5aR significantly reduced disease severity, suggesting that C5aR-mediated inflammation contributed to C3 glomerulopathy. Thus, C5 and C5aR have a critical role in C3 glomerulopathy. Hence, early intervention targeting these pathways may be an effective therapeutic strategy for patients with C3 glomerulopathy.

Murine systemic thrombophilia and hemolytic uremic syndrome from a factor H point mutation

Complement plays a key role in host defense, but its dysregulation can cause autologous tissue injury. Complement activation is normally controlled by regulatory proteins, including factor H (FH) in plasma and membrane cofactor protein (MCP) on the cell surface. Mutations in FH and MCP are linked to atypical hemolytic uremic syndrome, a type of thrombotic microangiopathy (TMA) that causes renal failure. We describe here that disruption of FH function on the cell surface can also lead to disseminated complement-dependent macrovascular thrombosis. By gene targeting, we introduced a point mutation (W1206R) into murine FH that impaired its interaction with host cells but did not affect its plasma complement-regulating activity. Homozygous mutant mice carrying this mutation developed renal TMA as well as systemic thrombophilia involving large blood vessels in multiple organs, including liver, lung, spleen, and kidney. Approximately 30% of mutant mice displayed symptoms of stroke and ischemic retinopathy, and 48% died prematurely. Genetic deficiency of complement C3 and factor D prevented both the systemic thrombophilia and renal TMA phenotypes. These results demonstrate a causal relationship between complement dysregulation and systemic angiopathy and suggest that complement activation may contribute to various human thrombotic disorders involving both the micro- and macrovasculature.

Modeling complement-driven diseases in transgenic mice: Values and limitations.

Remarkable advances have been made over past decades in understanding the pathogenesis of complement-mediated diseases. This has led to development of new therapies for, and in some cases re-classification of, complement-driven diseases. This success is due to not only insight from human patients but also studies using transgenic animal models. Animal models that mimic human diseases are useful tools to understand the mechanism of disease and develop new therapies but there are also limitations due to species differences in their complement systems. This review provides a summary of transgenic animal models for three human diseases that are at the forefront of anti-complement therapy, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). They are discussed here as examples to highlight the values and limitations of animal modeling in complement-driven diseases.

Blocking Properdin Prevents Complement-Mediated Hemolytic Uremic Syndrome and Systemic Thrombophilia

Background Properdin (P) is a positive regulator of the alternative pathway of complement activation. Although P inhibition is expected and has been shown to ameliorate the alternative pathway of complement-mediated tissue injury in several disease models, it unexpectedly exacerbated renal injury in a murine model of C3 glomerulopathy. The role of P in atypical hemolytic uremic syndrome (aHUS) is uncertain.Methods We blocked P function by genetic deletion or mAb-mediated inhibition in mice carrying a factor H (FH) point mutation, W1206R (FHR/R), that causes aHUS and systemic thrombophilia with high mortality.Results P deficiency completely rescued FHR/R mice from premature death and prevented thrombocytopenia, hemolytic anemia, and renal disease. It also eliminated macrovessel thrombi that were prevalent in FHR/R mice. All mice that received a function-blocking anti-P mAb for 8 weeks survived the experimental period and appeared grossly healthy. Platelet counts and hemoglobin levels were significantly improved in FHR/R mice after 4 weeks of anti-P mAb treatment. One half of the FHR/R mice treated with an isotype control mAb but none of the anti-P mAb-treated mice developed stroke-related neurologic disease. Anti-P mAb-treated FHR/R mice showed largely normal renal histology, and residual liver thrombi were detected in only three of 15 treated mice.Conclusions These results contrast with the detrimental effect of P inhibition observed in a murine model of C3 glomerulopathy and suggest that P contributes critically to aHUS pathogenesis. Inhibition of P in aHUS may be of therapeutic benefit.

Prevention of Fatal C3 Glomerulopathy by Recombinant Complement Receptor of the Ig Superfamily.

Background C3 glomerulopathy (C3G) is a life-threatening kidney disease caused by dysregulation of the alternative pathway of complement (AP) activation. No approved specific therapy is available for C3G, although an anti-C5 mAb has been used off-label in some patients with C3G, with mixed results. Thus, there is an unmet medical need to develop other inhibitors of complement for C3G.Methods We used a murine model of lethal C3G to test the potential efficacy of an Fc fusion protein of complement receptor of the Ig superfamily (CRIg-Fc) in the treatment of C3G. CRIg-Fc binds C3b and inhibits C3 and C5 convertases of the AP. Mice with mutations in the factor H and properdin genes (FHm/mP-/-) develop early-onset C3G, with AP consumption, high proteinuria, and lethal crescentic GN.Results Treatment of FHm/mP-/- mice with CRIg-Fc, but not a control IgG, inhibited AP activation and diminished the consumption of plasma C3, factor B, and C5. CRIg-Fc-treated FHm/mP-/- mice also had significantly improved survival and reduced proteinuria, hematuria, BUN, glomerular C3 fragment, C9 and fibrin deposition, and GN pathology scores.Conclusions Therapeutics developed on the basis of the mechanism of action of soluble CRIg may be effective for the treatment of C3G and should be explored clinically.

Antibody Inhibition of Properdin Prevents Complement-Mediated Intravascular and Extravascular Hemolysis

Paroxysmal nocturnal hemoglobinuria (PNH) is a serious blood disorder characterized by dysregulated complement activation on blood cells. Eculizumab, the current standard therapy and a humanized anti-C5 mAb, relieves anemia and thrombosis symptoms of PNH patients by preventing complement-dependent intravascular hemolysis (IVH). However, up to 20% of PNH patients on long-term eculizumab treatment still suffer from significant anemia and are transfusion dependent because of extravascular hemolysis (EVH) of C3-opsonized PNH erythrocytes. In this study, we show that function-blocking anti-properdin (P) mAbs dose-dependently inhibited autologous, complement-mediated hemolysis induced by factor H dysfunction. Furthermore, anti–human P (hP) mAbs potently and dose-dependently inhibited acidified serum–induced hemolysis of PNH erythrocytes (Ham test). In contrast to erythrocytes rescued by anti-C5 mAb, nonlysed PNH erythrocytes rescued by anti-P mAb incurred no activated C3 fragment deposition on their surface. These results suggested that anti-P mAbs may prevent EVH as well as IVH of PNH erythrocytes. To test the in vivo efficacy of anti-hP mAbs in preventing EVH, we generated a P humanized mouse by transgenic expression of hP in P knockout mice (hP-Tg/P−/−). In a murine EVH model, complement-susceptible erythrocytes were completely eliminated within 3 d in control mAb-treated hP-Tg/P−/− mice, whereas such cells were protected and persisted in hP-Tg/P−/− mice treated with an anti-hP mAb. Collectively, these data suggest that anti-P mAbs can inhibit both IVH and EVH mediated by complement and may offer improved efficacy over eculizumab, the current standard therapy for PNH.

Retinal Basal Laminar Deposits in Complement fH/fP Mouse Model of Dense Deposit Disease

Purpose Dense deposit disease (DDD) is caused by dysregulation of the alternative pathway of the complement cascade and characterized by electron-dense deposits in the kidney glomerular basement membrane (GBM) and drusen in Bruchs membrane (BrM). Complement factor H (fH) and factor properdin (fP) regulate complement activation; fH inhibits alternative pathway (AP) activation, whereas fP promotes it. We report pathologic changes in eyes of an fH and fP double-mutant mouse, which we previously showed have dense deposits in the GBM and early mortality from nephropathy. Methods fHm/m, fP−/−, and fHm/m/fP−/− mice were generated on a C57BL/6–129J background. Fundus imaging at 8 weeks of age was followed by analysis via light and electron microscopy. Retinal function was assessed by electroretinography (ERG). Complement levels and localization were tested by immunohistochemistry and ELISA. Retinas of fHm/m/fP−/− mice treated with intraperitoneal injections of an anti-C5 antibody were compared to those of age- and genotype-matched mice injected with an isotype control antibody. Results fHm/m/fP−/− mice suffered early-onset retinal hypopigmented spots detected using in vivo retinal photography, and histologic examination showed basal laminar deposits (BLamD), degeneration of the photoreceptors, and RPE vacuolization. ERG showed diminished retinal function. The anti-C5 antibody was retina-protective. Conclusions This unique mouse represents a new model of complement-mediated rapid-onset DDD, and could be useful in exploring the pathologic changes associated with BLamD in age-related macular degeneration.