Jiankun Zhu

Toll-Like Receptor Signaling Pathways—Therapeutic Opportunities

Toll-like receptors (TLRs) are transmembrane proteins acting mainly as sensors of microbial components. Triggering TLRs results in increased expression of multiple inflammatory genes, which then play a protective role against infection. However, aberrant activation of TLR signaling has a significant impact on the onset of cancer, allergy, sepsis and autoimmunity. Various adaptor proteins, including MyD88, IRAKs, TIRAP, TRIF, and TRAM, are involved in specific TLR signaling pathways. This article reviews the role of these molecules in TLR signaling, and discusses the impact of this pathway on various disease scenarios. Given their important role in infectious and non-infectious disease settings, TLRs and their signaling pathways emerge as attractive targets for therapeutics.

T cell hyperactivity in lupus as a consequence of hyperstimulatory antigen-presenting cells

Sle3 is an NZM2410-derived lupus susceptibility locus on murine chromosome 7. Congenic recombination has resulted in a novel mouse strain, B6.Sle3, associated with serum antinuclear autoantibodies (ANAs), T cell hyperactivity, and elevated CD4/CD8 ratios. An OVA-specific TCR transgene was used as a tool to demonstrate that Sle3 facilitated heightened T cell expansion in vitro, and in vivo, following antigen challenge. Indeed, continued T cell expansion was noted even in response to a tolerogenic signal. However, these phenotypes did not appear to be T cell intrinsic but were dictated by hyperstimulatory B6.Sle3 APCs. Importantly, B6.Sle3-derived DCs and macrophages appeared to be significantly more mature/activated, less apoptotic, and more proinflammatory and were better at costimulating T cells in vitro, compared with the B6 counterparts. Finally, the adoptive transfer of B6.Sle3-derived DCs into healthy B6 recipients elicited increased CD4/CD8 ratios and serum ANAs, 2 cardinal Sle3-associated phenotypes. We posit that their heightened expression of various costimulatory molecules, including CD80, CD106, I-A, and CD40, and their elevated production of various cytokines, including IL-12 and IL-1beta, may explain why Sle3-bearing DCs may be superior at breaching self tolerance. These studies provide mechanistic evidence indicating that intrinsic abnormalities in DCs and possibly other myeloid cells may dictate several of the phenotypes associated with systemic lupus, including ANA formation and T cell hyperactivity.

Innate Stimuli Accentuate End-Organ Damage by Nephrotoxic Antibodies via Fc Receptor and TLR Stimulation and IL-1/TNF-α 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-α, 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.

Adverse effects of simulated hyper- and hypo-phosphatemia on endothelial cell function and viability

Background Dysregulaiton of phosphate homeostasis as occurs in chronic kidney disease is associated with cardiovascular complications. It has been suggested that both hyperphosphatemia and hypophosphatemia can cause cardiovascular disease. The molecular mechanisms by which high or low serum phosphate levels adversely affect cardiovascular function are poorly understood. The purpose of this study was to explore the mechanisms of endothelial dysfunction in the presence of non-physiologic phosphate levels. Methodology/Principal Findings We studied the effects of simulated hyper- and hypophosphatemia in human umbilical vein endothelial cells in vitro. We found both simulated hyperphosphatemia and hypophosphatemia decrease eNOS expression and NO production. This was associated with reduced intracellular calcium, increased protein kinase C β2 (PKCβ2), reduced cell viability, and increased apoptosis. While simulated hyperphosphatemia was associated with decreased Akt/p-Akt, Bcl-xl/Bax ratios, NFkB-p65 and p-Erk abundance, simulated hypophosphatemia was associated with increased Akt/p-Akt and Bcl-xl/Bax ratios and p-Mek, p38, and p-p38 abundance. Conclusions/Significance This is the first demonstration of endothelial dysfunction with hypophosphatemia. Our data suggests that both hyperphosphatemia and hypophosphatemia decrease eNOS activity via reduced intracellular calcium and increased PKCβ2. Hyperphosphatemia also appears to reduce eNOS transcription via reduced signaling through PI3K/Akt/NF-kB and MAPK/NF-kB pathways. On the other hand, hypophosphatemia appears to activate these pathways. Our data provides the basis for further studies to elucidate the relationship between altered phosphate homeostasis and cardiovascular disease. As a corollary, our data suggests that the level of phosphate in the culture media, if not in the physiologic range, may inadvertently affect experimental results.

The Lupus-Susceptibility Locus, Sle3, Mediates Enhanced Resistance to Bacterial Infections

The genetic predisposition to many autoimmune diseases is inherited as a polygenic trait. It is conceivable that some of the causative alleles in these diseases became prevalent in the population by conferring a survival benefit against environmental assaults, such as infections. We used mice cogenic for genetic loci predisposing to systemic lupus erythomatosus to test the hypothesis that some of these genetic loci protect the host from bacterial infections. Mice with the Sle3 lupus-susceptibility locus on a wild-type background were found to have enhanced antibacterial responses in the context of pneumonia and intra-abdominal sepsis than wild-type animals. This was associated with markedly augmented accumulation of neutrophils in infected tissues, and was bone marrow transferable and dependent on the presence of neutrophils, but not lymphocytes. There was no difference in in vitro leukocyte killing of bacteria nor influx of phagocytes between lupus-susceptible and wild-type animals, but neutrophils from lupus-susceptible mice displayed markedly reduced rate of apoptosis, associated with altered expression of Bcl-2 family proteins, contributing to their greater accumulation. Importantly, deliberate inhibition of apoptosis in wild-type animals significantly boosted the accumulation of neutrophils at the site of infection and resulted in an enhanced antimicrobial response. These observations support the concept that some of the genetic loci that mediate autoimmunity may also confer augmented antimicrobial innate immunity.

Prevention of Murine Lupus Nephritis by Targeting Multiple Signaling Axes and Oxidative Stress Using a Synthetic Triterpenoid

Current treatment options for lupus are far from optimal. Previously, we reported that phosphatidylinositol 3‐kinase/Akt/mammalian target of rapamycin, MEK‐1/ERK‐1,2, p38, STAT‐3, STAT‐5, NF‐κB, multiple Bcl‐2 family members, and various cell cycle molecules were overexpressed in splenic B cells in an age‐dependent and gene dose–dependent manner in mouse strains with spontaneous lupus. Since the synthetic triterpenoid methyl‐2‐cyano‐3,12‐dioxooleana‐1,9‐dien‐28‐oate (CDDO‐Me) has been shown to inhibit AKT, MEK‐1/2, and NF‐κB, and to induce caspase‐mediated apoptosis, we tested the therapeutic potential of this agent in murine lupus nephritis.

Strain distribution pattern of immune nephritis—a follow-up study

Previous studies have indicated that the NZW, DBA/1, 129/sv and BUB strains are particularly sensitive to experimental anti-glomerular basement membrane (GBM)-induced immune nephritis. The present study extends previous observations by examining eight additional inbred mouse strains for their susceptibility to immune nephritis. Unlike the ALR/Lt, CAST/Ei, DDY/JclSidSeyFrk, FVB/NJ, PERA/Ei, SB/Le and BALB/c strains, the C58 mouse strain was observed to be particularly susceptible to experimental immune nephritis, with CBA mice being a close second. In contrast to the other strains, C58 mice uniformly developed heavy proteinuria, azotemia and severe glomerulonephritis with prominent crescent formation and tubulointerstitial nephritis following challenge with anti-GBM sera. These differences were associated with increased murine Ig deposition, leukocyte infiltration and IFN-gamma production within the kidneys of C58 mice. Studies aimed at elucidating the genetic factors and molecular pathways responsible for the enhanced renal disease in C58 mice are warranted.

Targeting multiple signaling axes and oxidative stress using a synthetic triterpenoid prevents murine lupus nephritis

Current treatment options for lupus are far from optimal. Previously, we reported that phosphatidylinositol 3‐kinase/Akt/mammalian target of rapamycin, MEK‐1/ERK‐1,2, p38, STAT‐3, STAT‐5, NF‐κB, multiple Bcl‐2 family members, and various cell cycle molecules were overexpressed in splenic B cells in an age‐dependent and gene dose–dependent manner in mouse strains with spontaneous lupus. Since the synthetic triterpenoid methyl‐2‐cyano‐3,12‐dioxooleana‐1,9‐dien‐28‐oate (CDDO‐Me) has been shown to inhibit AKT, MEK‐1/2, and NF‐κB, and to induce caspase‐mediated apoptosis, we tested the therapeutic potential of this agent in murine lupus nephritis.

Peritoneal catheter implantation elicits IL-10-producing immune-suppressor macrophages through a MyD88-dependent pathway

Catheters are implanted into the peritoneal cavity during the process of peritoneal dialysis. Though these catheters may be effective and beneficial, the impact of catheters on the immune system is poorly understood. Catheters and other devices implanted in the peritoneal cavity elicit a foreign body reaction. However, the immunological consequences of this remain uncharacterized. To model this, catheters were implanted into the peritoneal cavity of healthy mice. Catheter implantation induced rapid cellular changes within the peritoneal cavity. Whereas B-cells and T-cells were reduced, catheter implantation was associated with the rapid expansion of F4/80-low-positive, CD11b-positive macrophages that elaborated IL-10, and suppressed T-cell division and Th1 skewing in co-culture assays. Peritoneal catheter elicited macrophages had increased Jmjd3 but reduced NF-κB activation, and their emergence was MyD88-dependent. Collectively, these studies indicate that foreign body implantation into the peritoneal cavity is associated with the expansion of suppressor macrophages. Whether peritoneal cavity catheter implantation may have systemic immunoregulatory roles remains to be explored.

Prevention of Murine Lupus Nephritis by Targeting Multiple Signaling Axes and Oxidative Stress Using a Synthetic Triterpenoid: CDDO-Me Ameliorates Lupus

Current treatment options for lupus are far from optimal. Previously, we reported that phosphatidylinositol 3‐kinase/Akt/mammalian target of rapamycin, MEK‐1/ERK‐1,2, p38, STAT‐3, STAT‐5, NF‐κB, multiple Bcl‐2 family members, and various cell cycle molecules were overexpressed in splenic B cells in an age‐dependent and gene dose–dependent manner in mouse strains with spontaneous lupus. Since the synthetic triterpenoid methyl‐2‐cyano‐3,12‐dioxooleana‐1,9‐dien‐28‐oate (CDDO‐Me) has been shown to inhibit AKT, MEK‐1/2, and NF‐κB, and to induce caspase‐mediated apoptosis, we tested the therapeutic potential of this agent in murine lupus nephritis.