Different effects of global osteopontin and macrophage osteopontin in glomerular injury.

Osteopontin (OPN) is a pro-and anti-inflammatory molecule that simultaneously attenuates oxidative stress. Both inflammation and oxidative stress play a role in the pathogenesis of glomerulonephritis and in the progression of kidney injury. Importantly, OPN is highly induced in nephritic kidneys. To characterize further the role of OPN in kidney injury we used OPN-/- mice in antiglomerular basement membrane reactive serum-induced immune (NTS) nephritis, an inflammatory and progressive model of kidney disease. Normal wild-type (WT) and OPN-/- mice did not show histological differences. However, nephritic kidneys from OPN-/- mice showed severe damage compared with WT mice. Glomerular proliferation, necrotizing lesions, crescent formation, and tubulointerstitial injury were significantly higher in OPN-/- mice. Macrophage infiltration was increased in the glomeruli and interstitium in OPN-/- mice, with higher expression of IL-6, CCL2, and chemokine CXCL1. In addition, collagen (Col) I, Col III, and Col IV deposition were increased in kidneys from OPN-/- mice. Elevated expression of the reactive oxygen species-generating enzyme Nox4 and blunted expression of Nrf2, a molecule that inhibits reactive oxygen species and inflammatory pathways, was observed in nephritic kidneys from OPN-/- mice. Notably, CD11b diphteria toxin receptor mice with NTS nephritis selectively depleted of macrophages and reconstituted with OPN-/- macrophages showed less kidney injury compared with mice receiving WT macrophages. These findings suggest that in global OPN-/- mice there is increased inflammation and redox imbalance that mediate kidney damage. However, absence of macrophage OPN is protective, indicating that macrophage OPN plays a role in the induction and progression of kidney injury in NTS nephritis.

Macrophage A2A Adenosine Receptors Are Essential to Protect from Progressive Kidney Injury.

A2A adenosine receptors (A2ARs) are endogenous inhibitor of inflammation. Macrophages that are key effectors of kidney disease progression express A2ARs. We investigated the role of A2ARs in kidney inflammation in a macrophage-mediated anti-glomerular basement membrane reactive serum-induced immune nephritis in A2AR-deficient mice. Sub-threshold doses of glomerular basement membrane-reactive serum induced more severe and prolonged kidney damage with higher levels of proinflammatory cytokines and greater accumulation of inflammatory cells in A2AR(-/-) mice than wild-type (WT) mice. To investigate the role of macrophage A2AR in progressive kidney injury, glomerulonephritis was induced in CD11b-DTR transgenic mice. Macrophages were selectively depleted in the established phase of the disease and reconstituted with macrophages from WT or A2AR-deficient mice and then treated with an A2AR agonist. In mice receiving WT macrophages and treated with an A2AR agonist, the glomerular cellularity, crescent formation, sclerotic glomeruli, and tubulointerstitial injury were significantly reduced compared with the control group. In contrast, in mice reconstituted with A2AR-deficient macrophages and treated with an A2AR agonist, the kidney injury was more severe with increased deposition of collagen I, III, and IV. These findings suggest that disruption of the protective A2AR amplifies inflammation to accelerate glomerular damage and endogenous macrophage A2ARs are essential to protect from progressive kidney fibrosis.

Absence of nicotinic acetylcholine receptor α7 subunit amplifies inflammation and accelerates onset of fibrosis: an inflammatory kidney model.

Inflammation is regulated by endogenous mechanisms, including anti-inflammatory cytokines, adenosine, and the nicotinic acetylcholine receptor α7 subunit (α7nAChR). We investigated the role of α7nAChR in protection against the progression of tissue injury in a model of severe, macrophage-mediated, cytokine-dependent anti-glomerular basement membrane (GBM) glomerulonephritis (GN), in α7nAChR-deficient (α7(-/-)) mice . At d 7 after the injection of anti-GBM antibody, kidneys from α7(-/-) mice displayed severe glomeruli (P < 0.0001) and tubulointerstitial lesions (P < 0.001) compared to kidneys from WT mice. An important finding was the presence of severe glomerulosclerosis in α7(-/-) mice in this early phase of the disease. Kidneys of α7(-/-) mice showed greater accumulation of inflammatory cells and higher expression of chemokines and cytokines than did those of WT mice. In addition, in α7(-/-) fibrotic kidneys, the expression of fibrin, collagen, TGF-ß, and tissue inhibitor of metalloproteinase (TIMP)-2 increased, and the expression of TIMP3 declined. The increase in counterregulatory responses to inflammation in α7(-/-) nephritic kidneys did not compensate for the lack of α7nAChR. These findings indicate that α7nAChR plays a key role in regulating the inflammatory response in anti-GBM GN and that disruption of the endogenous protective α7nAChR amplifies inflammation to accelerate kidney damage and fibrosis.

Opposing activity changes in AMP deaminase and AMP-activated protein kinase in the hibernating ground squirrel.

Hibernating animals develop fatty liver when active in summertime and undergo a switch to a fat oxidation state in the winter. We hypothesized that this switch might be determined by AMP and the dominance of opposing effects: metabolism through AMP deaminase (AMPD2) (summer) and activation of AMP-activated protein kinase (AMPK) (winter). Liver samples were obtained from 13-lined ground squirrels at different times during the year, including summer and multiples stages of winter hibernation, and fat synthesis and ß-fatty acid oxidation were evaluated. Changes in fat metabolism were correlated with changes in AMPD2 activity and intrahepatic uric acid (downstream product of AMPD2), as well as changes in AMPK and intrahepatic ß-hydroxybutyrate (a marker of fat oxidation). Hepatic fat accumulation occurred during the summer with relatively increased enzymes associated with fat synthesis (FAS, ACL and ACC) and decreased enoyl CoA hydratase (ECH1) and carnitine palmitoyltransferase 1A (CPT1A), rate limiting enzymes of fat oxidation. In summer, AMPD2 activity and intrahepatic uric acid levels were high and hepatic AMPK activity was low. In contrast, the active phosphorylated form of AMPK and ß-hydroxybutyrate both increased during winter hibernation. Therefore, changes in AMPD2 and AMPK activity were paralleled with changes in fat synthesis and fat oxidation rates during the summer-winter cycle. These data illuminate the opposing forces of metabolism of AMP by AMPD2 and its availability to activate AMPK as a switch that governs fat metabolism in the liver of hibernating ground squirrel.

Human IL-32 expression protects mice against a hypervirulent strain of Mycobacterium tuberculosis.

Silencing of interleukin-32 (IL-32) in a differentiated human promonocytic cell line impairs killing of Mycobacterium tuberculosis (MTB) but the role of IL-32 in vivo against MTB remains unknown. To study the effects of IL-32 in vivo, a transgenic mouse was generated in which the human IL-32γ gene is expressed using the surfactant protein C promoter (SPC-IL-32γTg). Wild-type and SPC-IL-32γTg mice were infected with a low-dose aerosol of a hypervirulent strain of MTB (W-Beijing HN878). At 30 and 60 d after infection, the transgenic mice had 66% and 85% fewer MTB in the lungs and 49% and 68% fewer MTB in the spleens, respectively; the transgenic mice also exhibited greater survival. Increased numbers of host-protective innate and adaptive immune cells were present in SPC-IL-32γTg mice, including tumor necrosis factor-alpha (TNFα) positive lung macrophages and dendritic cells, and IFN-gamma (IFNγ) and TNFα positive CD4(+) and CD8(+) T cells in the lungs and mediastinal lymph nodes. Alveolar macrophages from transgenic mice infected with MTB ex vivo had reduced bacterial burden and increased colocalization of green fluorescent protein-labeled MTB with lysosomes. Furthermore, mouse macrophages made to express IL-32γ but not the splice variant IL-32ß were better able to limit MTB growth than macrophages capable of producing both. The lungs of patients with tuberculosis showed increased IL-32 expression, particularly in macrophages of granulomas and airway epithelial cells but also B cells and T cells. We conclude that IL-32γ enhances host immunity to MTB.

Endogenous Inhibitors of Kidney Inflammation.

Although inflammation is the physiological response to pathogen invasion and tissue damage, it can also be responsible for significant tissue damage. Therefore, the inflammatory response must be carefully regulated to prevent critical inflammatory damage to vital organs. Typically, local endogenous regulatory mechanisms adjust the magnitude of the response such that the injurious condition is resolved and homeostasis is mantained. Humoral mechanisms that restrain or inhibit inflammation include glucocorticoid hormones, anti-inflammatory cytokines such as IL-10 and transforming growth factor-ß (TGF-ß), and soluble cytokine receptors; other mediators facilitate tissue healing, like lipoxins and resolvins. There is growing evidence that inflammation plays a critical role in the development and progression of heart disease, cancer, stroke, diabetes, kidney diseases, sepsis, and several fibroproliferative disorders. Consequently, understanding the mechanisms that regulate inflammation may offer therapeutic targets for inhibiting the progression of several diseases. In this article, we review the significance of several novel endogenous anti-inflammatory mediators in the protection from kidney injury and the potential of these regulatory molecules as therapeutic targets for treatment of kidney inflammatory diseases.