Genetic predisposition of donors affects the allograft outcome in kidney transplantation; polymorphisms of stromal-derived factor-1 and CXC receptor 4

The Role of CXCL12 in Kidney Diseases: A Friend or Foe?

Background

Chemokines are a family of proteins mainly mediating the homing and migration of various cells. The CXC chemokine CXCL12 is a member of low-weight-molecular chemokines. In the kidney, CXCL12 is pivotal for renal development and exerts a modulatory effect in kidney diseases under different etiologic settings by binding with CXC chemokine receptor 4 (CXCR4) or CXC chemokine receptor 7 (CXCR7). Besides, CXCL12 also exerts homeostasis influence in diverse physical conditions and various pathological situations. Thus, we conclude the complicated relationship between CXCL12 and kidney diseases in this review.

Summary

In renal development, CXCL12 contributes a lot to nephrogenesis and the formation of renal vasculature via correlating with CXCR4. CXCL12 also plays an essential role in renal recovery from acute kidney injury. However, the CXCL12/CXCR4 axis plays a dual regulatory role in the initiation and development of diabetic kidney disease as well as chronic allogeneic nephropathy after kidney transplantation through dialectical consideration. Additionally, the CXCL12/CXCR4 link is considered as a new risk factor for lupus nephritis and renal cell carcinoma.

Key Messages

Plenty of studies have presented the influence of CXCL12 and the relation with corresponding receptors in diverse biological and pathological statuses. Simultaneously, some drugs and antagonists targeting CXCL12/CXCR4 axis effectively treat various kidney diseases. However, more researches are needed to explore thorough influence and mechanisms, providing more cues for clinical treatments.

Effects of Complement Regulators and Chemokine Receptors in Type 2 Diabetes

CD55 and CD59 are complement regulatory proteins suggested to be related with progression of diabetes and its complications. The stromal cell-derived factor 1 (SDF-1) and C-X-C chemokine receptor type 4 (CXCR-4) are chemokine proteins. We aimed to investigate the relation of CD55 and CD59 expression levels and polymorphisms of SDF-1 and CXCR-4 with type 2 diabetes mellitus (T2DM) and its complications. Seventy-five T2DM patients and 73 controls were enrolled. Expression levels of CD55 and CD59 were measured by FACS Calibur; qRT-PCR was used to determine SDF-1 and CXCR-4 gene polymorphisms. CD55 and CD59 expressions in patients with nephropathy, retinopathy and cardiovascular disease were significantly lower than controls. Frequency of CXCR-4 T allele carrying was high in patients and created 1.6 fold risk for the disease (p = .07). CXCR-4 a allele carriers had decreased nephropathy; although there was no statistical significance in carrying CXCR-4 T allele, presence of nephropathy was approximately 2 times higher (p = .254). The nephropathy risk increased 10-fold in CXCR-4 TT genotype carriers (p = .02). All SDF-1 CC genotype carriers had retinopathy, so, it was considered that the CC genotype was effective in retinopathy development (p = .031). For the presence of cardiovascular disease, significant difference was observed for SDF-1 genotypes. Increased cardiovascular risk of 5- and 1.9-fold in SDF-1 T (p = .007) and CXCR-4 T (p = .216) allele carriers, respectively, was observed. We suggest that CD55 and CD59 protein levels and SDF-1 and CXCR-4 have predictive importance in process, complications and tendency of T2DM.

Association of blood bicarbonate and pH with mineral metabolism disturbance and outcome after kidney transplantation

In kidney transplant recipients (KTRs), scarce evidence has associated low blood bicarbonate levels with mineral metabolic disturbance and reduced allograft survival. However, the contribution of the blood pH to these observations remains unassessed. Equally, little is known about the influence of the blood provenance (arteriovenous fistula vs peripheral vein) on bicarbonate values. We analyzed blood gas parameters in a single-center cohort of 1260 stable KTRs, 3 months after transplantation. Inspection of pO₂ distribution allowed the unambiguous identification of the arterial (N = 914) or venous (N = 346) origin of the samples. In patients with arterial blood samples, 435 (46%) had bicarbonate levels below 22 mmol/L. Among them, 196 (40%) were acidemic (blood pH <7.38). In multivariate analysis, low arterial blood pH was associated with increased blood ionized calcium and phosphate and reduced fibroblast growth factor 23 and calcitriol, but not with outcome. In contrast, low bicarbonate concentration predicted allograft loss independently of measured glomerular filtration rate and other potential confounders (hazard ratio [HR] 1.70; 95% confidence interval [CI] 1.04-2.80). In KTRs, reduced arterial blood bicarbonate levels predict outcome while acidemia is associated with altered mineral metabolism.

Analysis of genetic and clinical risk factors of post-transplant thrombocytopenia in kidney allograft recipients

BACKGROUND

Hematological abnormalities after transplantation are complications that may arise after renal transplantation, of which thrombocytopenia is associated with increased risk of bleeding and other complications. The development of thrombocytopenia is affected by various clinical conditions, and the stromal-derived factor 1 (SDF1) and platelet factor 4 (PF4) genes are known to be involved in the production or destruction of platelets. The purpose of this study was to investigate the prevalence of posttransplant thrombocytopenia and its association with other clinical conditions and genetic polymorphisms of SDF1 and PF4 genes a long time after transplantation.

METHODS

This is a retrospective study that includes a total of 305 kidney transplant (KT) recipients between 2008 and 2012 at St. Vincent Medical Center, Los Angeles, CA. In this study, posttransplant thrombocytopenia was defined as a 30% reduction in platelet count from the baseline in the first week or a decrease of <100 (×10³/μL) within 1 year after KT. The subjects were divided into posttransplant thrombocytopenia and control groups. The chi-square test, t-test, and logistic regression were used for the analyses.

RESULTS

In the first week, 65 patients had a 30% reduction in platelet count (21.3%). Gender, simultaneous kidney-pancreas transplantation, induction therapy (IT), and only alleles of rs2297630 of SDF1, among the SDF1 and PF4 genes, showed statistically significant differences. The rs2297630 alleles were consistently significant risk factors (non G vs. G: odds ratio = 0.445; 95% confidence interval, 0.224-0.884; p = .021) in the multiple logistic regression. In the 1-year study, 61 patients (20.0%) had platelet counts of <100 × 10³/μL and had statistically significant differences in patients who had delayed graft function and induction therapy.

CONCLUSIONS

In this study, non-G group of rs2297630 in SDF1 significantly increased the risk of post-transplant thrombocytopenia in the first week of kidney transplantation.

Integrative Analysis of Renal Ischemia/Reperfusion Injury and Remote Ischemic Preconditioning in Mice

Remote ischemic preconditioning (RIPC) is a strategy to induce resistance in a target organ against the oxidative stress and injury caused by ischemia and reperfusion (IR). RIPC harnesses the body's endogenous protective capabilities through brief episodes of IR applied in organs remote from the target. Few studies have analyzed this phenomenon in the kidney. Furthermore, the window of protection representing RIPC efficacy has not been fully elucidated. Here, we performed a multiomics study to specify those associated with protective effects of RIPC against the IR injury. A total of 30 mice were divided to four groups: sham, IR only, late RIPC + IR, and early RIPC + IR. We found that IR clearly led to tubular injury, whereas both preconditioning groups exhibited attenuated injury after the insult. In addition, renal IR injury produced changes of the metabolome in kidney, serum, and urine specimens. Furthermore, distinctive mRNA and associated protein expression changes supported potential mechanisms. Our findings revealed that RIPC effectively reduces renal damage after IR and that the potential mechanisms differed between the two time windows of protection. These results may potentially be extended to humans to allow non- or minimally invasive diagnosis of renal IR injury and RIPC efficacy.

Impact of kidney donor hemostasis on risk of complications after transplantation--preliminary outcomes

Background

This study analyzes the influence the of kidney donor hemostasis on the risk of complications in the kidney recipient after transplantation.

Material/Methods

We enrolled 38 deceased kidney donors, of whom14 donors died from a physical injury and the others died from ischemic or bleeding central nervous system stroke. The donors were categorized into 2 subgroups. If the recipient’s postoperative period proceeded smoothly, the kidney donor was assigned to the uncomplicated donors (UD) group. If the recipient’s postoperative period was complicated, the donor was assigned to the complicated (CD) Group. The CD group of consisted of 9 donors who died from strokes or bleedings and 2 who died from physical injury. We examined the antithrombin (AT) protein C (PC), complexes of thrombin/antithrombin (TAT), fragments F₁₊₂ of prothrombin (F₁₊₂), plasminogen (Pl), complexes of plasmin/antiplasmin (PAP), and D-dimers (D-d).

Results

In the CD group had decreased activity of AT, PC, and Pl and increased activity of F₁₊₂, TAT, and D-d. The UD group had a higher level of PAP. The CD group had evidence of intensive blood coagulation, but the UD group had evidence of fibrinolysis. Fisher’s exact test revealed an increased risk in recipients who received a kidney from the CD group.

Conclusions

The hemostasis of the kidney donors had a correlation with the occurrence of some complications in the kidney recipients, especially complications connected with activation of blood coagulation. It seems that the activation of fibrinolysis could be positive prognostic factor, but this requires further investigations.

The genetics of kidney transplantation

Over the last decade, the search for gene variants with the potential to influence transplant outcomes or predispose individuals to host-recipient-related phenotypes has generated a considerable number of studies with conflicting results. Thousands of genotypes have been associated with complex traits related to transplant medicine, including acute rejection, immunosuppressive drug metabolism and side effects, infections, long-term outcomes, and cardiovascular complications. However, these efforts have given disappointing results, both in terms of gaining understanding of the biological basis of disease and in patient management. The methodological weaknesses that constitute the major limitations of most of these studies have been discussed widely. A new generation of approaches is needed to understand the relationship between gene variants and complex kidney transplantation traits. These approaches should be global, to generate original pathophysiological hypotheses, and should rely on advanced genomic tools, including Genome Wide Association studies and Whole Genome Sequencing technologies. Such enterprises will only be successful with the creation of international consortiums that connect partners in clinical, industrial, and academic transplant medicine.

Validation of genetic variants associated with early acute rejection in kidney allograft transplantation

Numerous reports have identified genetic variants associated with kidney transplant outcome, but only a few have been validated in subsequent studies. We analyzed the association of 21 previously reported genetic variants associated with acute rejection (AR), in an effort to validate these associations in our kidney transplant population. All recipients (n = 585) received Ab induction, rapid discontinuation of prednisone, and calcineurin inhibitors with either mycophenolate mofetil or sirolimus. Both univariate analysis and logistic regression were used for determining the association between the genotypes and AR. Univariate analysis detected one significant single-nucleotide polymorphism (p = 0.03), rs1801133, within the methylenetetrahydrofolate reductase (MTHFR) gene associated with AR. Logistic regression analysis identified two variants associated with AR, the 32-bp deletion within chemokine (C-C motif) receptor 5 gene (rs333) and the p.222A/V variant (rs1801133) within the MTHFR gene. Although our analysis utilized a much larger cohort than used in previous reports, we were only able to detect an association with two of these variants. The lack of validation for the other 19 variants may be due to the small effect size, or that, they are not associated with AR. These results stress the need for larger cohorts for both future studies as well as for validation studies.