The Macrophage Mediates the Renoprotective Effects of Endotoxin Preconditioning

Preconditioning is a preventative approach, whereby minimized insults generate protection against subsequent larger exposures to the same or even different insults. In immune cells, endotoxin preconditioning downregulates the inflammatory response and yet, preserves the ability to contain infections. However, the protective mechanisms of preconditioning at the tissue level in organs such as the kidney remain poorly understood. Here, we show that endotoxin preconditioning confers renal epithelial protection in various models of sepsis in vivo. We also tested the hypothesis that this protection results from direct interactions between the preconditioning dose of endotoxin and the renal tubules. This hypothesis is on the basis of our previous findings that endotoxin toxicity to nonpreconditioned renal tubules was direct and independent of immune cells. Notably, we found that tubular protection after preconditioning has an absolute requirement for CD14-expressing myeloid cells and particularly, macrophages. Additionally, an intact macrophage CD14-TRIF signaling pathway was essential for tubular protection. The preconditioned state was characterized by increased macrophage number and trafficking within the kidney as well as clustering of macrophages around S1 proximal tubules. These macrophages exhibited increased M2 polarization and upregulation of redox and iron-handling molecules. In renal tubules, preconditioning prevented peroxisomal damage and abolished oxidative stress and injury to S2 and S3 tubules. In summary, these data suggest that macrophages are essential mediators of endotoxin preconditioning and required for renal tissue protection. Preconditioning is, therefore, an attractive model to investigate novel protective pathways for the prevention and treatment of sepsis.     

Gomisin A decreases the LPS-induced expression of iNOS and COX-2 and activation of RIP2/NF-κB in mouse peritoneal macrophages

Gomisin A (GA), a lignan component contained in the fruit of Schisandra chinensis Baillon, improves hepatic cell degeneration, vasodilatory activity and insulin sensitivity. These effects also impact the immune system, including various inflammatory mediators and cytokines. In this study, the anti-inflammatory effect of GA on lipopolysaccharide-stimulated mouse peritoneal macrophages was studied. Pretreatment with GA attenuated the expression of receptor-interacting protein 2 (RIP2) and IκB kinase-β (IKK-β) as well as IKK-β phosphorylation. The activation of nuclear factor-kappa B (NF-κB) in the nucleus, the phosphorylation of IκBα and degradation of IκBα in the cytosol were suppressed by GA. GA decreased the production and mRNA expression of the inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6. In addition, expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and production of nitric oxide were decreased by pretreatment with GA. In conclusion, these results show that the anti-inflammatory properties of GA potentially result from the inhibition of COX-2, iNOS, IL-6, TNF-α and NO through the down-regulation of RIP2 and NF-κB activation. These results impact the development of potential health products for preventing and treating inflammatory diseases.     

Rapid‐onset clinical and mechanistic effects of anti‐C5aR treatment in the mouse collagen‐induced arthritis model

Preclinical evidence supports targeting the C5a receptor (C5aR) in rheumatoid arthritis (RA). To support ongoing clinical development of an anti‐C5aR monoclonal antibody, we have investigated for the first time the mechanism of action and the pharmacodynamics of a blocking anti‐murine C5aR (anti‐mC5aR) surrogate antibody in mouse collagen‐induced arthritis (CIA). First, efficacy was demonstrated in a multiple‐dose treatment study. Almost complete inhibition of clinical disease progression was obtained, including reduced bone and cartilage destruction in anti‐mC5aR‐treated mice. Then, the mechanism of action was examined by looking for early effects of anti‐mC5aR treatment in single‐dose treatment studies. We found that 48 h after single‐dose treatment with anti‐mC5aR, the neutrophil and macrophage infiltration into the paws was already reduced. In addition, several inflammatory markers, including tumour necrosis factor (TNF)‐α, interleukin (IL)‐6 and IL‐17A were reduced locally in the paws, indicating reduction of local inflammation. Furthermore, dose‐setting experiments supported a beneficial clinical effect of dosing above the C5aR saturation level. In conclusion, these preclinical data demonstrated rapid onset effects of antibody blockade of C5aR. The data have translational value in supporting the Novo Nordisk clinical trials of an anti‐C5aR antibody in rheumatoid arthritis patients, by identifying potential biomarkers of treatment effects as well as by providing information on pharmacodynamics and novel insights into the mechanism of action of monoclonal antibody blockade of C5aR.     

An update on leptin as immunomodulator

Until the discovery of leptin 20 years ago, adipose tissue was considered only as a fat storage organ, involved in the regulation of energy homeostasis. At present, it is well known that adipokines, being leptin the forerunner of this superfamily, may act in different biological processes, including inflammation and immunity. In this review, we have explored the recent evidence about the relationship between leptin and immune system, summarizing the most important findings related to the involvement of leptin in both innate and adaptive immune response.     

Systematic review of mouse kidney transplantation

A mouse model of kidney transplantation was first described in 1973 by Skoskiewicz et al. Although the mouse model is technically difficult, it is attractive for several reasons: the mouse genome has been characterized and in many aspects is similar to man and there is a greater diversity of experimental reagents and techniques available for mouse studies than other experimental models. We reviewed the literature on all studies of mouse kidney transplantation to report the donor and recipient strain combinations that have been investigated and the resultant survival and histological outcomes. Some models of kidney transplantation have used the transplanted kidney as a life‐supporting organ, however, in many studies the recipient mouse's native kidney has been left in situ. Several different combinations of inbred mouse strains have been reported, with varying degrees of injury, survival or tolerance because of haplotype differences. This model has been exceptionally useful as an investigational tool to understand multiple aspects of transplantation including acute rejection, cellular and humoral rejection mechanisms and their treatment. Furthermore, this model has been used to investigate disease mechanisms beyond transplant rejection including intrinsic renal disease and infection‐associated pathology.     

Microglial polarization and plasticity: Evidence from organotypic hippocampal slice cultures

Increasing evidence indicates that “functional plasticity” is not solely a neuronal attribute but a hallmark of microglial cells, the main brain resident macrophage population. Far from being a univocal phenomenon, microglial activation can originate a plethora of functional phenotypes, encompassing the classic M1 proinflammatory and the alternative M2 anti‐inflammatory phenotypes. This concept overturns the popular view of microglial activation as a synonym of neurotoxicity and neurogenesis failure in brain disorders. The characterization of the alternative programs is a matter of intense investigation, but still scarce information is available on the course of microglial activation, on the reversibility of the different commitments and on the capability of preserving molecular memory of previous priming stimuli. By using organotypic hippocampal slice cultures as a model, we developed paradigms of stimulation aimed at shedding light on some of these aspects. We show that persistent stimulation of TLR4 signaling promotes an anti‐inflammatory response and microglial polarization toward M2‐like phenotype. Moreover, acute and chronic preconditioning regimens permanently affect the capability to respond to a later challenge, suggesting the onset of mechanisms of molecular memory. Similar phenomena could occur in the intact brain and differently affect the vulnerability of mature and newborn neurons to noxious signals. GLIA 2013;61:1698–1711     

Salmonella-induced SipB-independent cell death requires Toll-like receptor-4 signalling via the adapter proteins Tram and Trif

Salmonella enterica serovar typhimurium (S. typhimurium) is an intracellular pathogen that causes macrophage cell death by at least two different mechanisms. Rapid cell death is dependent on the Salmonella pathogenicity island-1 protein SipB whereas delayed cell death is independent of SipB and occurs 18-24 hr post infection. Lipopolysaccharide (LPS) is essential for the delayed cell death. LPS is the main structural component of the outer membrane of Gram-negative bacteria and is recognized by Toll-like receptor 4, signalling via the adapter proteins Mal, MyD88, Tram and Trif. Here we show that S. typhimurium induces SipB-independent cell death through Toll-like receptor 4 signalling via the adapter proteins Tram and Trif. In contrast to wild type bone marrow derived macrophages (BMDM), Tram(-/-) and Trif(-/-) BMDM proliferate in response to Salmonella infection.     

Neuroprotective role of the innate immune system by microglia

Innate immunity is a rapid series of reactions to pathogens, cell injuries and toxic proteins. A key component of this natural response is the production of inflammatory mediators by resident microglia and infiltrating macrophages. There is accumulating evidence that inflammation contributes to acute injuries and more chronic CNS diseases, though other studies have shown that inhibition of microglia is, in contrast, associated with more damages or less repair. The controversies regarding the neuroprotective and neurodegenerative properties of microglia may depend on the experimental approaches. Neurotoxic substances are frequently used to produce animal models of acute injuries or diseases and they may activate microglia either directly or indirectly by their ability to cause neuronal death and demyelination. Whether microglia and the immune response play a direct role in such processes still remains an open question. On the other hand, there are data supporting the role of resident microglia and those derived from the bone marrow in the stimulation of myelin repair, removal of toxic proteins from the CNS and the prevention of neurodegeneration in chronic brain diseases. The ability of glucocorticoids to provide a negative feedback on nuclear factor kappa B pathways in microglia may be a determinant mechanism underlying the ultimate fate of the inflammatory response in the CNS. This review presents new concepts regarding the neuroprotective role of the innate immune response in the brain and how microglia can be directed to improve recovery after injuries and prevent/delay neurodegeneration.