Naoka Murakami

G2A Is a Proton-sensing G-protein-coupled Receptor Antagonized by Lysophosphatidylcholine

G2A (from G2 accumulation) is a G-protein-coupled receptor (GPCR) that regulates the cell cycle, proliferation, oncogenesis, and immunity. G2A shares significant homology with three GPCRs including ovarian cancer GPCR (OGR1/GPR68), GPR4, and T cell death-associated gene 8 (TDAG8). Lysophosphatidylcholine (LPC) and sphingosylphosphorylcholine (SPC) were reported as ligands for G2A and GPR4 and for OGR1 (SPC only), and a glycosphingolipid psychosine was reported as ligand for TDAG8. As OGR1 and GPR4 were reported as proton-sensing GPCRs (Ludwig, M. G., Vanek, M., Guerini, D., Gasser, J. A., Jones, C. E., Junker, U., Hofstetter, H., Wolf, R. M., and Seuwen, K. (2003) Nature 425, 93–98), we evaluated the proton-sensing function of G2A. Transient expression of G2A caused significant activation of the zif 268 promoter and inositol phosphate (IP) accumulation at pH 7.6, and lowering extracellular pH augmented the activation only in G2A-expressing cells. LPC inhibited the pH-dependent activation of G2A in a dose-dependent manner in these assays. Thus, G2A is another proton-sensing GPCR, and LPC functions as an antagonist, not as an agonist, and regulates the proton-dependent activation of G2A.

Risk of Metabolic Complications in Kidney Transplantation After Conversion to mTOR Inhibitor: A Systematic Review and Meta‐Analysis

Mammalian target of rapamycin (mTOR) inhibitors have been used in transplantation with the hope of minimizing calcineurin inhibitor (CNI)‐induced nephrotoxicity. However, mTOR inhibitors are also associated with a range of side effects, including metabolic complications. We aimed to determine the risks of metabolic complications after the conversion from CNI to mTOR inhibitor postkidney transplant. A systematic search in PubMed up to September 2013 identified nine relevant trials (a total of 2323 patients). The primary end points were the relative risks (RRs) of new‐onset diabetes after transplant (NODAT) and hypercholesterolemia. The overall RRs of NODAT and hypercholesterolemia associated with mTOR inhibitors were 1.32 (95% confidence interval [CI] 0.92–1.87) and 2.15 (95% CI 1.35–3.41), respectively, compared with CNI‐based regimen. Subgroup analyses revealed no differences in the incidence of NODAT or hypercholesterolemia between sirolimus‐ versus everolimus‐based regimen, or between early versus late conversion. Analyses of secondary outcomes revealed a higher risk of acute rejection, proteinuria and anemia, but no difference in the risk of opportunistic infections after mTOR inhibitor conversion. In conclusion, the conversion from CNI to mTOR inhibitor in low‐to‐moderate risk kidney transplant recipients was associated with nonsignificant trend toward increased risk of NODAT and significant increase in hypercholesterolemia, acute rejection, proteinuria and anemia.

Severe acute interstitial nephritis after combination immune-checkpoint inhibitor therapy for metastatic melanoma

Immune-checkpoint inhibitors are emerging as revolutionary drugs for certain malignancies. However, blocking the co-inhibitory signals may lead to immune-related adverse events, mainly in the spectrum of autoimmune diseases including colitis, endocrinopathies and nephritis. Here, we report a case of a 75-year-old man with metastatic malignant melanoma treated with a combination of nivolumab (anti-PD1-antibody) and ipilimumab (anti-CTLA-4 antibody) who developed systemic rash along with severe acute tubulointerstitial nephritis after two doses of combination therapy. Kidney biopsy and peripheral blood immune profile revealed highly proliferative and cytotoxic T cell features. Herein, we discuss the pathophysiology and management of immune checkpoint blockade-related adverse events.

Co-inhibitory pathways and their importance in immune regulation.

Immune regulation is critical for the maintenance of peripheral self-tolerance and for down-regulation of immune responses. Understanding its mechanisms may permit the development of novel targets for the promotion of tolerance in transplantation. Co-inhibitory molecules play a major role in modulating T-cell receptor signaling upon antigen encounter. Their unique patterns of expression, structure, and binding partners account for their diverse function and non-redundancy. Moreover, these inhibitory signals have active roles in both effector and regulatory immune cells in multiple sites, including the target tissue. Herein, we review the recent advances in our understanding of co-inhibitory signaling and its potential clinical applications, focusing mainly on the two best-characterized receptors CTLA4 and PD-1. Recent observations in cancer clinical trials using blocking antibodies against PD-1 or CTLA4, or both, showed a high incidence of autoimmune-related side effects, confirming the important role of these pathways in human immune homeostasis.

Immunophenotyping and Efficacy of Low Dose ATG in Non-Sensitized Kidney Recipients Undergoing Early Steroid Withdrawal: A Randomized Pilot Study

Rabbit antithymocyte globulin (ATG) is commonly used as an induction therapy in renal transplant recipients, but the ideal dosage in tacrolimus-based early steroid withdrawal protocols has not been established. The purpose of this pilot study was to determine the immunophenotyping and efficacy of lower dose ATG in low immunological-risk kidney transplant recipients. In this prospective study, 45 patients were randomized (1∶1) to our standard dose ATG (total dose 3.75 mg/kg)(sATG) vs. lower dose 2.25 mg/kg (lowATG). All patients underwent early steroid withdrawal within 7 days. The primary end point was biopsy-proven acute rejection at 12 months. Prospective immunophenotyping of freshly isolated PBMCs was performed at baseline, 3, 6, 12 months post-transplant. The rate of acute rejection was 17% and 10% in the sATG and lowATG, respectively. Effector memory T cells, Tregs and recent thymic emigrants T cells had similar kinetics post-transplant in both groups. No statistically significant differences were found in graft survival, patient survival or infections between the two groups, though there was a non-significant increase in leukopenia (43%v s. 30%), CMV (8% vs. 0) and BK (4% vs. 0) infections in sATG group vs. lowATG. In sum, in low immunological risk kidney recipients undergoing steroid withdrawal, low dose ATG seems to be efficacious in preventing acute rejection and depleting T cells with potentially lower infectious complications. A larger study is warranted to confirm these findings. Trial Registration ClinicalTrials.gov NCT00548405

Renal complications of immune checkpoint blockade

Immune checkpoint inhibitors have been approved for a variety of cancer species. Renal complications in use of these agents are not very common compared with other immune-related adverse events (irAE). However, it is crucial for physicians to recognize and manage renal manifestations of irAE. In this review, we will summarize the up-to-date knowledge of the clinical presentation, pathologic features, and management of renal irAE. In addition, we will discuss the safety of immune checkpoint inhibitors in patients with chronic kidney disease as well as in kidney transplant recipients.

Visualization of the pH-dependent dynamic distribution of G2A in living cells

G2A (from G2 accumulation) receptor is a member of the proton‐sensing G‐protein coupled receptor (GPCR) family and induces signal transduction events that regulate the cell cycle, proliferation, oncogenesis, and immunity. The mechanism by which G2A‐mediated signal transduction is regulated by the extracellular pH remains unresolved. Here, we first visualize the pH‐dependent G2A distribution change in living cells by a sortase A‐mediated pulse labeling technology: the short‐peptide tag‐fused human G2A on human embryo kidney HEK293T cell surfaces was labeled with a small fluorescent dye in the presence of lysophosphatidylcholine, and the labeled G2A was chased at acidic and neutral pHs in real time by microscope time course observations. G2A internalization from cell surfaces into intracellular compartments was observed to be inhibited under acidic pH conditions, and this inhibition was relieved at neutral pH. Additionally, the internalized G2A was redistributed onto cell surfaces by jumping from a neutral to an acidic pH. From quantitative image analysis data, we conclude the amount of G2A on the cell surface was controlled by suppressing the G2A internalization rate by one‐tenth in response to the extracellular acidic pH, and this acidic pH‐induced G2A accumulation on cell surfaces may be explained by proton‐induced dissociation of G2A from endocytic machinery.—Lan, W., Yamaguchi, S., Yamamoto, T., Yamahira, S., Tan, M., Murakami, N., Zhang, J., Nakamura, M., Nagamune, T. Visualization of the pH‐dependent dynamic distribution of G2A in living cells. FASEB J. 28, 3965‐3974 (2014). www.fasebj.org

Codominant Role of Interferon-γ– and Interleukin-17–Producing T Cells During Rejection in Full Facial Transplant Recipients

Facial transplantation is a life‐changing procedure for patients with severe composite facial defects. However, skin is the most immunogenic of all transplants, and better understanding of the immunological processes after facial transplantation is of paramount importance. Here, we describe six patients who underwent full facial transplantation at our institution, with a mean follow‐up of 2.7 years. Seum, peripheral blood mononuclear cells, and skin biopsy specimens were collected prospectively, and a detailed characterization of their immune response (51 time points) was performed, defining 47 immune cell subsets, 24 serum cytokines, anti‐HLA antibodies, and donor alloreactivity on each sample, producing 4269 data points. In a nonrejecting state, patients had a predominant T helper 2 cell phenotype in the blood. All patients developed at least one episode of acute cellular rejection, which was characterized by increases in interferon‐γ/interleukin‐17–producing cells in peripheral blood and in the allografts skin. Serum monocyte chemotactic protein‐1 level was significantly increased during rejection compared with prerejection time points. None of the patients developed de novo donor‐specific antibodies, despite a fourfold expansion in T follicular helper cells at 1 year posttransplantation. In sum, facial transplantation is frequently complicated by a codominant interferon‐γ/interleukin‐17–mediated acute cellular rejection process. Despite that, medium‐term outcomes are promising with no evidence of de novo donor‐specific antibody development.

Transcriptional regulation of human G2A in monocytes/ macrophages: involvement of c/EBPs, Runx and Pu.1

G2 accumulation (G2A) is a G‐protein coupled receptor, activated by several ligands and stimuli, such as lysophosphatidylcholine (LPC), extracellular low pH and oxidized phospholipids including 9‐ and 13‐hydroxyoctadecadienoic acid, and has been implicated in mediating inflammatory process under oxidative conditions. Recently, it was demonstrated that G2A in monocytes/macrophages plays critical roles in atherosclerosis deterioration, and therefore its transcriptional regulation in monocytes/macrophages is of great interest. Here, we first confirmed the expression of human G2A (hG2A) in lymph nodes, spleen and peripheral blood leukocytes, including monocytes. Thereafter, transcription start site (TSS) of hG2A was determined by 5′‐rapid amplification of cDNA ends analysis. In the course of the analysis, we found that two transcriptional variants, hG2A‐a and ‐b, are produced by alternative splicing, resulting in the production of N‐terminal different hG2A proteins with similar sensitivity to low pH and LPC. Using a monocytic cell line THP‐1 as a model, transcription of hG2A was precisely examined, and we demonstrated that it is dependent both on the chromatin structure around TSS, and on the binding of the transcription factors (c/EBPα and β, Runx1 and Pu.1) to their cis‐elements, located at the core promoter just upstream of TSS.

Disaster Preparedness and Awareness of Patients on Hemodialysis after Hurricane Sandy

BACKGROUND AND OBJECTIVES Patients with ESRD on dialysis live in a complex sociomedical situation and are dependent on technology and infrastructure, such as transportation, electricity, and water, to sustain their lives. Interruptions of this infrastructure by natural disasters can result in devastating outcomes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Between November of 2013 and April of 2014, a cross-sectional survey was conducted of patients who received maintenance hemodialysis before and after the landfall of Hurricane Sandy on October 29, 2012 in lower Manhattan, New York. The primary outcome was the number of missed dialysis sessions after the storm. Dialysis-specific and general disaster preparedness were assessed using checklists prepared by the National Kidney Foundation and US Homeland Security, respectively. RESULTS In total, 598 patients were approached, and 357 (59.7%) patients completed the survey. Participants were 60.2% men and 30.0% black, with a median age of 60 years old; 94 (26.3%) participants missed dialysis (median of two sessions [quartile 1 to quartile 3 =1-3]), and 236 (66.1%) participants received dialysis at nonregular dialysis unit(s): 209 (58.5%) at affiliated dialysis unit(s) and 27 (7.6%) at emergency rooms. The percentages of participants who carried their insurance information and detailed medication list were 75.9% and 44.3%, respectively. Enhancement of the dialysis emergency packet after the hurricane was associated with a significantly higher cache of medical records at home at follow-up survey (P<0.001, Fishers exact test). Multivariate Poisson regression analysis showed that dialysis-specific preparedness (incidence rate ratio, 0.91; 95% confidence interval, 0.87 to 0.98), other racial ethnicity (incidence rate ratio, 0.34; 95% confidence interval, 0.20 to 0.57), dialysis treatment in affiliated units (incidence rate ratio, 0.69; 95% confidence interval, 0.51 to 0.94), and older age (incidence rate ratio, 0.98; 95% confidence interval, 0.97 to 0.99) were associated with a significantly lower incidence rate ratio of missed dialysis. CONCLUSIONS There is still room to improve the preparedness for natural disasters of patients with ESRD. Provider- or facility-oriented enhancement of awareness of the disease and preparedness should be a priority.