Chaker N. Adra

Immunomodulation by Mesenchymal Stem Cells A Potential Therapeutic Strategy for Type 1 Diabetes

Mesenchymal stem cells (MSCs) are pluripotent stromal cells that have the potential to give rise to cells of diverse lineages. Interestingly, MSCs can be found in virtually all postnatal tissues. The main criteria currently used to characterize and identify these cells are the capacity for self-renewal and differentiation into tissues of mesodermal origin, combined with a lack in expression of certain hematopoietic molecules. Because of their developmental plasticity, the notion of MSC-based therapeutic intervention has become an emerging strategy for the replacement of injured tissues. MSCs have also been noted to possess the ability to impart profound immunomodulatory effects in vivo. Indeed, some of the initial observations regarding MSC protection from tissue injury once thought mediated by tissue regeneration may, in reality, result from immunomodulation. Whereas the exact mechanisms underlying the immunomodulatory functions of MSC remain largely unknown, these cells have been exploited in a variety of clinical trials aimed at reducing the burden of immune-mediated disease. This article focuses on recent advances that have broadened our understanding of the immunomodulatory properties of MSC and provides insight as to their potential for clinical use as a cell-based therapy for immune-mediated disorders and, in particular, type 1 diabetes.

Immunomodulatory Function of Bone Marrow-Derived Mesenchymal Stem Cells in Experimental Autoimmune Type 1 Diabetes

Human clinical trials in type 1 diabetes (T1D) patients using mesenchymal stem cells (MSC) are presently underway without prior validation in a mouse model for the disease. In response to this void, we characterized bone marrow-derived murine MSC for their ability to modulate immune responses in the context of T1D, as represented in NOD mice. In comparison to NOD mice, BALB/c-MSC mice were found to express higher levels of the negative costimulatory molecule PD-L1 and to promote a shift toward Th2-like responses in treated NOD mice. In addition, transfer of MSC from resistant strains (i.e., nonobese resistant mice or BALB/c), but not from NOD mice, delayed the onset of diabetes when administered to prediabetic NOD mice. The number of BALB/c-MSC trafficking to the pancreatic lymph nodes of NOD mice was higher than in NOD mice provided autologous NOD-MSC. Administration of BALB/c-MSC temporarily resulted in reversal of hyperglycemia in 90% of NOD mice (p = 0.002). Transfer of autologous NOD-MSC imparted no such therapeutic benefit. We also noted soft tissue and visceral tumors in NOD-MSC-treated mice, which were uniquely observed in this setting (i.e., no tumors were present with BALB/c- or nonobese resistant mice-MSC transfer). The importance of this observation remains to be explored in humans, as inbred mice such as NOD may be more susceptible to tumor formation. These data provide important preclinical data supporting the basis for further development of allogeneic MSC-based therapies for T1D and, potentially, for other autoimmune disorders.

Atopy and asthma: genetic variants of IL-4 and IL-13 signalling

Abstract Recent genetic and functional studies highlight the importance of IL-4/IL-13 signalling in the development of asthma and atopy. Here, Taro Shirakawa and colleagues discuss genetic variants of IL-4/IL-13 signalling, and whether they promote asthma or atopy among different ethnic groups.

A TRPV2–PKA Signaling Module for Transduction of Physical Stimuli in Mast Cells

Cutaneous mast cell responses to physical (thermal, mechanical, or osmotic) stimuli underlie the pathology of physical urticarias. In vitro experiments suggest that mast cells respond directly to these stimuli, implying that a signaling mechanism couples functional responses to physical inputs in mast cells. We asked whether transient receptor potential (vanilloid) (TRPV) cation channels were present and functionally coupled to signaling pathways in mast cells, since expression of this channel subfamily confers sensitivity to thermal, osmotic, and pressure inputs. Transcripts for a range of TRPVs were detected in mast cells, and we report the expression, surface localization, and oligomerization of TRPV2 protein subunits in these cells. We describe the functional coupling of TRPV2 protein to calcium fluxes and proinflammatory degranulation events in mast cells. In addition, we describe a novel protein kinase A (PKA)–dependent signaling module, containing PKA and a putative A kinase adapter protein, Acyl CoA binding domain protein (ACBD)3, that interacts with TRPV2 in mast cells. We propose that regulated phosphorylation by PKA may be a common pathway for TRPV modulation.

Functional promoter polymorphism in the TBX21 gene associated with aspirin-induced asthma

Asthma is a phenotypically heterogeneous disorder with many etiologic factors and clinical characteristics. T-bet, a Th1-specific transcription factor of T-box family, has been found to control interferon-γ (IFN-γ) expression in T cells. Mice lacking the T-bet gene (tbx21) demonstrate multiple physiological and inflammatory features reminiscent of human asthma. In order to examine whether polymorphisms in the candidate gene, TBX21, located on chromosome 17q21.32, are related to the risk of human asthma phenotypes, we have searched for genetic variations in the human TBX21 gene and identified 24 single nucleotide polymorphisms (SNPs), including five novel SNPs, by direct sequencing in Japanese subjects. Among asthma phenotypes, a promoter −1993T→C SNP, which is in linkage disequilibrium with a synonymous coding 390A→G SNP in exon 1, is significantly associated with a risk of aspirin-induced asthma (AIA; P=0.004, Pc=0.016). This association has also been confirmed in additional independent samples of asthma with nasal polyposis (P=0.008), regardless of aspirin hypersensitivity. Furthermore, our data indicate that the −1993T→C substitution increases the affinity of a particular nuclear protein to the binding site of TBX21 covering the −1993 position, resulting in increased transcriptional activity of the TBX21 gene. Thus, in addition to the antigen-driven excess Th2 response, increased T-bet (and subsequent IFN-γ) production in human airways of individuals with the −1993T→C polymorphism could contribute to the development of certain asthma-related phenotypes, such as AIA.

Human HTm4 is a hematopoietic cell cycle regulator

Proper control of cell cycle progression is critical for the constant self-renewal, differentiation, and homeostasis of the hematopoietic system. Cells of all types share the common cell cycle regulators. The different expression patterns of common regulators, in a broad sense, define cell-type or lineage specificity. However, there remains the possibility of hematopoietic cell cycle regulators tailored to the demands of the hematopoietic system. Here we describe a novel protein, HTm4, which serves as a hematopoietic cell cycle regulator. Our data indicate that HTm4 is expressed in hematopoietic tissues and is tightly regulated during the differentiation of hematopoietic stem cells. It binds to cyclin-dependent kinase-associated (CDK-associated) phosphatase-CDK2 (KAP-CDK2) complexes, and the three proteins demonstrate similar patterns of cellular expression in human lymphoid tissues. HTm4 stimulates the phosphatase activity of KAP, and its C-terminal region is required for binding to KAP-CDK2 complexes and the modulation of KAP activity. Overexpression of HTm4 can cause cell cycle arrest at the G(0)/G(1) phase. Thus, HTm4 is a novel hematopoietic modulator for the G(1)-S cell cycle transition.

Inhibition of hematopoietic development from embryonic stem cells by antisense vav RNA.

The vav proto‐oncogene is universally and specifically expressed in hematopoietic cells. vav contains a unique array of motifs allowing the protein to function as a signal transducer and possibly as a transcription factor. Under certain in vitro culture conditions murine embryonic stem cells develop into colonies containing multiple hematopoietic lineages. In embryonic stem cell lines, constitutively expressing high levels of antisense vav transcripts through a stably integrated transgene, differentiation into hematopoietic cells is disrupted. This observation presents the first evidence that vav has a critical role in the development of hematopoietic cells from totipotent cells.

Anti-inflammatory potential of CB1-mediated cAMP elevation in mast cells

Cannabinoids are broadly immunosuppressive, and anti-inflammatory properties have been reported for certain marijuana constituents and endogenously produced cannabinoids. The CB2 cannabinoid receptor is an established constituent of immune system cells, and we have recently established that the CB1 cannabinoid receptor is expressed in mast cells. In the present study, we sought to define a role for CB1 in mast cells and to identify the signalling pathways that may mediate the suppressive effects of CB1 ligation on mast cell activation. Our results show that CB1 and CB2 mediate diametrically opposed effects on cAMP levels in mast cells. The observed long-term stimulation of cAMP levels by the Galpha(i/o)-coupled CB1 is paradoxical, and our results indicate that it may be attributed to CB1-mediated transcriptional regulation of specific adenylate cyclase isoenzymes that exhibit superactivatable kinetics. Taken together, these results reveal the complexity in signalling of natively co-expressed cannabinoid receptors and suggest that some anti-inflammatory effects of CB1 ligands may be attributable to sustained cAMP elevation that, in turn, causes suppression of mast cell degranulation.

RGA protein associates with a TRPV ion channel during biosynthesis and trafficking.

TRPV ion channels transduce a range of temperature stimuli. We proposed that analysis of the protein–protein interactions made by TRPV2 might give insight into the key issues surrounding this channel. These issues include the potential functional significance of TRPV2 in non‐sensory tissues, the molecules involved in transducing its activation signal(s) and the mechanism by which its trafficking to the cell surface is regulated. Here we describe the interaction of TRPV2 channel with the RGA gene product. RGA is a four‐transmembrane domain, intracellularly localized protein. RGA associates with TRPV2 in a rat mast cell line that is a native context for both proteins. The interaction between TRPV2 and RGA is transient and occurs intracellularly. RGA does not accompany TRPV2 to the cell surface. Formation of the TRPV2/RGA complex is dependent upon a cellular glycosylation event, suggesting that RGA may play a chaperone or targeting role for TRPV2 during the maturation of the ion channel protein. These data record a novel protein–protein interaction for TRPV2 and provide a foundation for future study of the potential regulatory contribution of RGA to TRPV2 function.

Transplant tourism outcome: a single center experience.

Background. Transplant tourism is the term used for patients who travel abroad for transplantation. Transplant tourism has always been surrounded with controversy regarding how these organs were obtained, the donors care after transplantation, and the recipient outcome. Many authors have found that the outcome of the recipients in transplant tourism is inferior to those transplanted in their own countries. However, most these studies were small, with the latest one including only 33 patients. Here, we describe the outcome of 93 patients who were transplanted abroad compared with local transplantation. Material and Methods. All transplant patients who were followed up at our Nephrology Clinic from 1998 until 2008 were identified using our data base system. We selected patients transplanted from 2003 and forward because the computerized system for laboratory and electronic records began operation that year. Results. A total of 165 patients were identified (93 in the tourist group and 72 in the local one). Transplant tourists had a higher rate of acute rejection in the first year compared with local transplantation (27.9% vs. 9.9, P=0.005), higher mean creatinine at 6 months and 1 year (120 vs. 101 &mgr;mol/L, P=0.0007, 113 vs. 98 &mgr;mol/L, P=0.008). There was no statistical difference in graft or patient survival in 1 or 2 years after transplantation. However, transplant tourist had a higher rate of cytomegalovirus infection (15.1% vs. 5.6%, P=0.05) and hepatitis C seroconversion (7.5% vs. 0%, P=0.02). Conclusion. Transplant tourists had a more complex posttransplantation course with higher incidence of acute rejection and infectious complications.