Abstract

Biology of Chronic Graft-versus-host Disease: Implications for a Future Therapeutic Approach

Paul J. Martin

Hematopoietic cell transplantation (HCT) is frequently complicated by graft-versus-host disease (GVHD). During the past three decades, experimental studies and clinical observations have elucidated the pathophysiology of acute GVHD, but the biology of chronic GVHD is much less well understood. Recommendations of the NIH Consensus Development Project on Criteria for Clinical Trials in Chronic GVHD have begun to standardize the diagnosis and clinical assessment of the disease. These criteria have emphasized the importance of qualitative differences, as opposed to time of onset after HCT, in making the distinction between acute and chronic GVHD. Experimental studies have generated at least four theories to explain the pathophysiology of chronic GVHD. These theories include 1) thymic damage and defective negative selection of T cells generated from marrow progenitors after HCT, 2) aberrant production of transforming growth factor-β, 3) auto-antibody production, and 4) deficiency of T-regulatory cells. Recent studies in humans have corroborated a possible role for each of these mechanisms in humans. No animal model fully replicates all of the features of chronic GVHD in humans, and it appears likely that multiple biological mechanisms account for the diverse features the disease. Chronic GVHD may represent a "syndrome" with diverse causes among individual patients. In the future, it might become possible to tailor specific therapeutic interventions for patients as individually needed for each distinct pathophysiologic mechanism involved in development of the disease.

Investigation of Oxalate and Urolithiasis over 30 years with Emphasis on Oxalosis

Yoshihide Ogawa

Oxalate is well known to increase the urinary calcium oxalate saturation, potentially resulting in renal stone formation. There are a variety of factors that influence the urinary concentrations of oxalate, calcium, and other stone-related substances. In addition, there is diurnal variation of urinary calcium oxalate saturation. Urinary oxalate excretion is influenced by four factors, which are dietary oxalate absorption, endogenous oxalate production from precursors, vitamin B6 deficiency, and hyperoxaluria (types 1 & 2). Magnesium and citrate alkaline salts have been shown to inhibit stone formation. Dietary intake of oxalate has an important influence on urinary oxalate excretion, while dietary calcium and magnesium block oxalate absorption and lead to its degradation by bacteria in the colon. Various precursors (including glyoxylate, glycolate, ethylene glycol, hydroxypyruvate, hydroxyproline, and xylitol) are metabolized to form oxalate and this metabolic process is augmented by vitamin B6 deficiency. Two glyoxylate-detoxifying enzymes (AGT and GRHPR) are defective in primary hyperoxaluria and vitamin B6 deficiency mimics the knock-down state of both enzymes. So far, combined liver and kidney transplantation is the only way to salvage patients with primary hyperoxaluria type 1 (AGT deficiency). This is a rare disease that presents early in life with renal failure. It is hard to make a diagnosis of primary hyperoxaluria in patients with chronic renal failure because they tend to have a high blood oxalate level. Vitamin C is required for dialysis patients to utilize iron, but excessive intake may cause hyperoxalemia because of its conversion to oxalate.

Barrier Dysfunction Due to Defensin Deficiency in Crohn's Disease

Eduard F. Stange

Different clinical localizations of CD are associated with different deficiencies in epithelial and leukocyte antimicrobial peptide expression. As compared to UC, Crohn's disease of the colon is characterized by an impaired induction of beta defensins, antimicrobial antiproteases elafin and SLPI as well as the cathelicidin LL37. The attenuated induction of beta defensins is linked to fewer gene copy numbers in this locus which is associated with colonic but not ileal CD. In contrast, ileal Crohn's disease patients are characterized by a reduced antibacterial activity and a specific reduction of ileal Paneth cell defensins. This decrease is independent of the grade of histological inflammation and cannot be found in inflammation controls. In ileal Crohn's patients displaying a NOD2 mutation, this decrease is even more pronounced. Thus, some of these defects can be explained either by direct or indirect genetic mechanisms and appear to be primary.
Unlike UC, ileal and colonic CD are characterized by localization specific deficiencies of antibacterial peptides. Understanding the precise molecular mechanisms of the defective antibacterial barrier function might provide new therapeutic directions aimed at stimulating protective innate immune functions.

Cellular and Molecular Mechanisms of OPG and RANKL and their Involvement in the Pathophysiology of Osteoarthritis

Steeve Kwan Tat, Jean-Pierre Pelletier, Carmen Ruiz Velasco, Marc Padrines, and Johanne Martel-Pelletier

Bone remodelling is tightly regulated by a molecular triad composed of OPG/RANK/RANKL. The receptor activator of NF-κB ligand (RANKL) (localized on osteoblasts) enhances osteoclastogenesis via interaction with its receptor RANK (localized on osteoclasts), whereas osteoprotegerin (OPG) (produced by osteoblasts) inhibits this osteoclastogenesis by binding RANKL. The equilibrium between OPG and RANKL plays a crucial role in the pathophysiology of bone. Although some studies have shown the efficacy of OPG as a therapeutic agent against bone resorption, its bio-availability and mechanism of action after binding to RANKL remains to be determined. The group in Nantes (France) conducted a mechanistic investigation based on the becoming of OPG after binding to RANKL cells, which demonstrated an internalization of OPG through the clathrin pathway before proteasomal and/or lysosomal degradation. This OPG internalisation process reduced the half-life of RANKL.
Osteoarthritis is the most common arthritic disease, and recent evidence has shown that the subchondral bone alteration is intimately involved in cartilage degradation and loss, and that OPG/RANKL may be implicated. Indeed, with the Montreal group (Canada), we showed that human osteoarthritic subchondral bone osteoblasts had an abnormal OPG and RANKL level and consequently an altered OPG/RANKL ratio. Further data also revealed the involvement of some osteotropic factors in this abnormal ratio and that treatment with such factors generally targets RANKL with a differential modulation of each RANKL isoform. Altogether, data suggest that OPG or RANKL could be targeted as new strategies for the treatment of osteoarthritis.

Role of the Renin-Angiotensin System in the Development of the Ureteric Bud and Renal Collecting System

Ihor V. Yosypiv

Defects in ureteric bud (UB) morphogenesis result in congenital abnormalities of the kidney and urinary tract (CAKUT). The developing metanephros expresses all the components of the renin-angiotensin system (RAS). Mutations in the genes encoding components of the RAS in mice cause renal papillary hypoplasia, hydronephrosis, and urinary concentrating defect. We tested the hypothesis that papillary hypoplasia in RAS-deficient mice is secondary to an intrinsic defect in the development of the UB and the renal medulla. We demonstrated that: 1) UB and surrounding stroma express angiotensinogen and angiotensin (Ang) II AT₁ receptors (AT₁R) in vivo; 2) Ang II stimulates UB cell process extension, branching and cord formation in collagen gel cultures in vitro as well as UB branching in the intact metanephroi obtained from Hoxb7-GFP transgenic mice grown ex vivo; 3) Ang II induces tyrosine phosphorylation of epidermal growth factor receptor (EGFR) in UB cells. Ang II-induced UB branching is attenuated by inhibition of EGFR tyrosine kinase activity; 4) Ang II-induced effects on UB branching and EGFR tyrosine phosphorylation are abrogated by AT₁R antagonism with candesartan. These data demonstrate that Ang II, acting via the AT₁R, stimulates UB branching and that cooperation of AT₁R and EGFR signaling is important in UB morphogenesis and development of the renal collecting system.

Dendritic Cells as Tolerogens

Alexander H. Enk

The "classical" role of a dendritic cells (DC) is to induce potent immune responses in vertebrates. However, it is known for some time that DC can also subserve as inducers of immune tolerance. As an in vivo example, DC resident in tumor tissue or tumor-infiltrated lymph nodes have been shown to induce anergic or even regulatory T cells. Cytokines such as IL-10 and TGFβ released by tumor infiltrating cells seem to be instrumental for this process, that even leads to the expansion of regulatory T cells. Thus there is experimental evidence that tumors actively convert immune responses triggered by DC to tolerogenic signals. The molecular target structures that are modified during this process encompass costimulatory signals, antigen presentation and release of immunomodulatory cytokines.
The fact that especially immature DC seem to exert tolerogenic functions might also be used therapeutically. Strategies using targeting of antigens to immature DC have been developed. A very potent strategy is targeting using the antigen receptor DEC-205. Binding of the antibody does not lead to activation of DC. Thus, coupling of antigens to anti-DEC mAb results in antigen presentation by immature DC and the induction of regulatory T cells (Tregs). This induction process can be used in the induction of tolerance in autoimmune models such as murine EAE and might be of value for future therapies in human autoimmunity. The construction of single chain mAb might further facilitate this strategy.