Link between immune cell infiltration and mitochondria-induced cardiomyocyte death during acute cardiac graft rejection

Cyclophilin D Regulates the Nuclear Translocation of AIF, Cardiac Endothelial Cell Necroptosis and Murine Cardiac Transplant Injury

Ischemia-reperfusion injury (IRI) is an inevitable consequence of organ transplant procedure and associated with acute and chronic organ rejection in transplantation. IRI leads to various forms of programmed cell death, which worsens tissue damage and accelerates transplant rejection. We recently demonstrated that necroptosis participates in murine cardiac microvascular endothelial cell (MVEC) death and murine cardiac transplant rejection. However, MVEC death under a more complex IRI model has not been studied. In this study, we found that simulating IRI conditions in vitro by hypoxia, reoxygenation and treatment with inflammatory cytokines induced necroptosis in MVECs. Interestingly, the apoptosis-inducing factor (AIF) translocated to the nucleus during MVEC necroptosis, which is regulated by the mitochondrial permeability molecule cyclophilin D (CypD). Furthermore, CypD deficiency in donor cardiac grafts inhibited AIF translocation and mitigated graft IRI and rejection (n = 7; p = 0.002). Our studies indicate that CypD and AIF play significant roles in MVEC necroptosis and cardiac transplant rejection following IRI. Targeting CypD and its downstream AIF may be a plausible approach to inhibit IRI-caused cardiac damage and improve transplant survival.

Circulating mitochondrial genes detect acute cardiac allograft rejection: Role of the mitochondrial calcium uniporter complex

Acute rejection after heart transplantation increases the risk of chronic dysfunction. Disturbances in mitochondrial function may play a contributory role, however, the relationship between histological signs of rejection in the human transplanted heart and expression levels of circulating mitochondrial genes, such as the mitochondrial Ca²⁺ uniporter (MCU) complex, remains unexplored. We conducted an RNA-sequencing analysis to identify altered mitochondrial genes in serum and to evaluate their diagnostic accuracy for rejection episodes. We included 40 consecutive samples from transplant recipients undergoing routine endomyocardial biopsies. In total, 112 mitochondrial genes were identified in the serum of posttransplant patients, of which 28 were differentially expressed in patients with acute rejection (p < .05). Considering the receiver operating characteristic analysis with an area under the curve (AUC) >0.900 to discriminate patients with moderate or severe degrees of rejection, we found that the MCU system showed a strong capability for detection: MCU (AUC = 0.944, p < .0001), MCU/MCUR1 ratio (AUC = 0.972, p < .0001), MCU/MCUB ratio (AUC = 0.970, p < .0001), and MCU/MICU1 ratio (AUC = 0.970, p < .0001). Mitochondrial alterations are reflected in peripheral blood and are capable of discriminating between patients with allograft rejection and those not experiencing rejection with excellent accuracy. The dysregulation of the MCU complex was found to be the most relevant finding.

Markers of Immune Function in Heart Transplantation: Implications for Immunosuppression and Screening for Rejection

PURPOSE OF REVIEW

Recent developments in high-throughput DNA and RNA sequencing technologies have facilitated the development of noninvasive assays to monitor heart transplant rejection. In this review, we summarize existing assays employed for the surveillance of allograft rejection, as well as promising future directions for such tests in the molecular biology field.

RECENT FINDINGS

The AlloMap genome expression profiling assay remains the only noninvasive test for rejection surveillance and is incorporated into the International Society of Heart and Lung Transplantation guidelines. Other efforts have focused on messenger RNA (mRNA), microRNA (miRNA), and donor-derived cell-free DNA (dd-cfDNA) as potential viable biomarkers. Mitochondrial pathways in allograft necroptosis and inflammation signaling may represent a novel direction for future research endeavors. Although endomyocardial biopsy remains the gold standard, several converging areas of molecular biology could soon yield successful alternative methods of heart transplant rejection monitoring, with the distinct advantage of avoiding procedural complications.

Mitochondrial permeability regulates cardiac endothelial cell necroptosis and cardiac allograft rejection

Transplantation is invariably associated with programmed cell death including apoptosis and necrosis, resulting in delayed graft function and organ rejection. We have demonstrated the contribution of necroptosis to mouse microvascular endothelial cell (MVEC) death and transplant rejection. Organ injury results in the opening of mitochondrial permeability transition pores (mPTPs), which can trigger apoptotic molecules release that ultimately results in cell death. The effect of mPTPs in the necroptotic pathway remains controversial; importantly, their role in transplant rejection is not clear. In this study, tumor necrosis factor-α triggered MVECs to undergo receptor-interacting protein kinase family (RIPK1/3)-dependent necroptosis. Interestingly, inhibition of mPTP opening could also inhibit necroptotic cell death. Cyclophilin-D (Cyp-D) is a key regulator of the mPTPs. Both inhibition and deficiency of Cyp-D protected MVECs from necroptosis (n = 3, P < .00001). Additionally, inhibition of Cyp-D attenuated RIPK3-downstream mixed-lineage kinase domain-like protein phosphorylation. In vivo, Cyp-D-deficient cardiac grafts showed prolonged survival in allogeneic BALB/c mice posttransplant compared with wild-type grafts (n = 7, P < .0001). Our study results suggest that the mPTPs may be important mechanistic mediators of necroptosis in cardiac grafts. There is therapeutic potential in targeting cell death via inhibition of the mPTP-regulating molecule Cyp-D to prevent cardiac graft rejection.

Impact of Mitochondrial Permeability on Endothelial Cell Immunogenicity in Transplantation

BACKGROUND

Microvascular endothelial cells (ECs) are central to an allograft's immunogenicity. Cold ischemia and reperfusion injury associated with static cold storage and warm reperfusion activates ECs and increases the immunogenicity of the allograft. After reperfusion, mitochondrial permeability transition pore (mPTP) opening contributes to mitochondrial dysfunction in the allograft, which correlates to alloimmune rejection. Current understanding of this relationship, however, centers on the whole allograft instead of ECs. This study aimed to elucidate the relationship between EC mPTP opening and their immunophenotype.

METHODS

Mitochondrial metabolic fitness and glycolysis in ECs were assessed in parallel with metabolic gene microarray postreperfusion. NIM811 was used to inhibit mPTP opening to rescue mitochondrial fitness. The immunogenicity of NIM811-treated ECs was determined via levels of EC's proinflammatory cytokines and allogeneic CD8 T cell cocultures. Finally, EC surface expression of adhesion, costimulatory, coinhibitory, MHC-I molecules, and MHC-I machinery protein levels were characterized.

RESULTS

Genes for glycolysis, tricarboxylic acid cycle, fatty acid synthesis, gluconeogenesis were upregulated at 6 hours postreperfusion but either normalized or downregulated at 24 hours postreperfusion. As mitochondrial fitness was reduced, glycolysis increased during the first 6 hours postreperfusion. Endothelial cell treatment with NIM811 during the early postreperfusion period rescued mitochondrial fitness and reduced EC immunogenicity by decreasing CCL2, KC release, and VCAM-1, MHC-I, TAP1 expression.

CONCLUSIONS

Static cold storage and warm reperfusion leads to a reduction in mitochondrial fitness in microvascular ECs due to mPTP opening. Further, mPTP opening promotes increased EC immunogenicity that can be prevented by NIM811 treatment.

Expression of Mitochondrial-Encoded Genes in Blood Differentiate Acute Renal Allograft Rejection

Despite potent immunosuppression, clinical and biopsy confirmed acute renal allograft rejection (AR) still occurs in 10-15% of recipients, ~30% of patients demonstrate subclinical rejection on biopsy, and ~50% of them can show molecular inflammation, all which increase the risk of chronic dysfunction and worsened allograft outcomes. Mitochondria represent intracellular endogenous triggers of inflammation, which can regulate immune cell differentiation, and expansion and cause antigen-independent graft injury, potentially enhancing the development of acute rejection. In the present study, we investigated the role of mitochondrial DNA encoded gene expression in biopsy matched peripheral blood (PB) samples from kidney transplant recipients. Quantitative PCR was performed in 155 PB samples from 115 unique pediatric (<21 years) and adult (>21 years) renal allograft recipients at the point of AR (n = 61) and absence of rejection (n = 94) for the expression of 11 mitochondrial DNA encoded genes. We observed increased expression of all genes in adult recipients compared to pediatric recipients; separate analyses in both cohorts demonstrated increased expression during rejection, which also differentiated borderline rejection and showed an increasing pattern in serially collected samples (0-3 months prior to and post rejection). Our results provide new insights on the role of mitochondria during rejection and potentially indicate mitochondria as targets for novel immunosuppression.

Lebetin 2, a Snake Venom-Derived Natriuretic Peptide, Attenuates Acute Myocardial Ischemic Injury through the Modulation of Mitochondrial Permeability Transition Pore at the Time of Reperfusion

Cardiac ischemia is one of the leading causes of death worldwide. It is now well established that natriuretic peptides can attenuate the development of irreversible ischemic injury during myocardial infarction. Lebetin 2 (L2) is a new discovered peptide isolated from Macrovipera lebetina venom with structural similarity to B-type natriuretic peptide (BNP). Our objectives were to define the acute cardioprotective actions of L2 in isolated Langendorff-perfused rat hearts after regional or global ischemia-reperfusion (IR). We studied infarct size, left ventricular contractile recovery, survival protein kinases and mitochondrial permeability transition pore (mPTP) opening in injured myocardium. L2 dosage was determined by preliminary experiments at its ability to induce cyclic guanosine monophosphate (cGMP) release without changing hemodynamic effects in normoxic hearts. L2 was found to be as effective as BNP in reducing infarct size after the induction of either regional or global IR. Both peptides equally improved contractile recovery after regional IR, but only L2 increased coronary flow and reduced severe contractile dysfunction after global ischemia. Cardioprotection afforded by L2 was abolished after isatin or 5-hydroxydecanote pretreatment suggesting the involvement of natriuretic peptide receptors and mitochondrial K_ATP (mitoK_ATP) channels in the L2-induced effects. L2 also increased survival protein expression in the reperfused myocardium as evidenced by phosphorylation of signaling pathways PKCε/ERK/GSK3β and PI3K/Akt/eNOS. IR induced mitochondrial pore opening, but this effect was markedly prevented by L2 treatment. These data show that L2 has strong cardioprotective effect in acute ischemia through stimulation of natriuretic peptide receptors. These beneficial effects are mediated, at least in part, by mitoK_ATP channel opening and downstream activated survival kinases, thus delaying mPTP opening and improving IR-induced mitochondrial dysfunction.

Mitochondrial DNA disturbances and deregulated expression of oxidative phosphorylation and mitochondrial fusion proteins in sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is one of the most common myopathies in elderly people. Mitochondrial abnormalities at the histological level are present in these patients. We hypothesize that mitochondrial dysfunction may play a role in disease aetiology. We took the following measurements of muscle and peripheral blood mononuclear cells (PBMCs) from 30 sIBM patients and 38 age- and gender-paired controls: mitochondrial DNA (mtDNA) deletions, amount of mtDNA and mtRNA, mitochondrial protein synthesis, mitochondrial respiratory chain (MRC) complex I and IV enzymatic activity, mitochondrial mass, oxidative stress and mitochondrial dynamics (mitofusin 2 and optic atrophy 1 levels). Depletion of mtDNA was present in muscle from sIBM patients and PBMCs showed deregulated expression of mitochondrial proteins in oxidative phosphorylation. MRC complex IV/citrate synthase activity was significantly decreased in both tissues and mitochondrial dynamics were affected in muscle. Depletion of mtDNA was significantly more severe in patients with mtDNA deletions, which also presented deregulation of mitochondrial fusion proteins. Imbalance in mitochondrial dynamics in muscle was associated with increased mitochondrial genetic disturbances (both depletion and deletions), demonstrating that proper mitochondrial turnover is essential for mitochondrial homoeostasis and muscle function in these patients.

Apollon/RNF41 myocardial messenger RNA diagnoses cardiac allograft apoptosis in rejection

BACKGROUND

Endomyocardial biopsy (EMB) remains the gold standard for acute cellular rejection (ACR) diagnosis in cardiac transplantation yet is subject to interobserver variability. A method that could avoid discordant EMB analysis would be desirable. The apoptosis rate in EMB correlates with ACR severity. Apollon inhibits apoptosis, and RNF41 catalyzes its degradation. Whether tissue Apollon/RNF41 could diagnose ACR is not known. This study addressed this issue.

METHODS

Apollon/RNF41 messenger RNA (mRNA) was measured by real time reverse-transcriptase polymerase chain reaction and apoptosis was quantified with TUNEL assays in EMBs of 268 transplant recipients. EMBs were obtained at 1, 2, 3, 4, 7, 12, 24, and 52 posttransplant weeks.

RESULTS

At all time points posttransplant, Apollon mRNA decreased significantly in EMBs with ACR grades 2R/3R combined (P<or=0.0010) compared with 0/1R combined, although RNF41 mRNA significantly increased in EMBs with ACR grade 1R (P<0.0001) or 2R/3R combined (P<0.0001) compared with 0. At the identified cut-off level of less than or equal to 168.2 arbitrary units, Apollon mRNA identified ACR grades 2R/3R with 100% sensitivity and 84% specificity, whereas RNF41 mRNA at the cut-off level of more than or equal to 51.8 identified ACR grades 1R-3R with 99% sensitivity and 95% specificity. Increased RNF41 (rs, 0.728; P<0.0001) and decreased Apollon (rs, -0.562; P<0.0001) expression correlated significantly with the degree of apoptosis in EMBs.

CONCLUSIONS

Combined Apollon/RNF41 mRNA quantitatively and specifically identifies ACR associated with apoptosis in cardiac allografts and could validate ACR grading variability associated with histologic EMB analysis.

Inhibition of GSK3β by Postconditioning Is Required to Prevent Opening of the Mitochondrial Permeability Transition Pore During Reperfusion

Background— Opening of the mitochondrial permeability transition pore (mPTP) is a crucial event in lethal reperfusion injury. Phosphorylation (inhibition) of glycogen synthase kinase-3β (GSK3β) has been involved in cardioprotection. We investigated whether phosphorylated GSK3β may protect the heart via the inhibition of mPTP opening during postconditioning.

Methods and Results— Wild-type and transgenic GSK3β-S9A mice (the cardiac GSK3β activity of which cannot be inactivated) underwent 60 minutes of ischemia and 24 hours of reperfusion. At reperfusion, wild-type and GSK3β-S9A mice received no intervention (control), postconditioning (3 cycles of 1 minute ischemia and 1 minute of reperfusion), the mPTP inhibitor cyclosporine A (CsA; 10 mg/kg IV), or the GSK3β inhibitor SB216763 (SB21; 70 μg/kg IV). Infarct size was assessed by triphenyltetrazolium chloride staining. The resistance of the mPTP to opening after Ca 2+ loading was assessed by spectrofluorometry on mitochondria isolated from the area at risk. In wild-type mice, infarct size was significantly reduced by postconditioning, CsA, and SB21, averaging 39±2%, 35±5%, and 37±4%, respectively, versus 58±5% of the area at risk in control mice ( P <0.05). In GSK3β-S9A mice, only CsA, but not postconditioning or SB21, reduced infarct size. Postconditioning, CsA, and SB21 all improved the resistance of the mPTP in wild-type mice, but only CsA did so in GSK3β-S9A mice.

Conclusion— These results suggest that S9-phosphorylation of GSK3β is required for postconditioning and likely acts by inhibiting the opening of the mitochondrial permeability transition pore.

Inhibition of mitochondrial permeability transition improves functional recovery and reduces mortality following acute myocardial infarction in mice

Inhibition of mitochondrial permeability transition pore (mPTP) opening by cyclosporin A or ischemic postconditioning attenuates lethal reperfusion injury. Its impact on major post-myocardial infarction events, including worsening of left ventricular (LV) function and death, remains unknown. We sought to determine whether pharmacological or postconditioning-induced inhibition of mPTP opening might improve functional recovery and survival following myocardial infarction in mice. Anesthetized mice underwent 25 min of ischemia and 24 h (protocol 1) or 30 days (protocol 2) of reperfusion. At reperfusion, they received no intervention (control), postconditioning (3 cycles of 1 min ischemia-1 min reperfusion), or intravenous injection of the mPTP inhibitor Debio-025 (10 mg/kg). At 24 h of reperfusion, mitochondria were isolated from the region at risk for assessment of the Ca(2+) retention capacity (CRC). Infarct size was measured by triphenyltetrazolium chloride staining. At 30 days of reperfusion, mortality and LV contractile function (echocardiography) were evaluated. Postconditioning and Debio-025 significantly improved Ca(2+) retention capacity (132 +/- 13 and 153 +/- 31 vs. 53 +/- 16 nmol Ca(2+)/mg protein in control) and reduced infarct size to 35 +/- 4 and 32 +/- 7% of area at risk vs. 61 +/- 6% in control (P < 0.05). At 30 days, ejection fraction averaged 74 +/- 6 and 77 +/- 6% in postconditioned and Debio-025 groups, respectively, vs. 62 +/- 12% in the control group (P < 0.05). At 30 days, survival was improved from 58% in the control group to 92 and 89% in postconditioned and Debio-025 groups, respectively. Inhibition of mitochondrial permeability transition at reperfusion improves functional recovery and mortality in mice.

Determination of N-methyl-4-isoleucine-cyclosporin (NIM811) in human whole blood by high performance liquid chromatography-tandem mass spectrometry

A liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the determination of N-methyl-4-isoleucine-cyclosporin (NIM811) was developed and validated over the concentration range 1-2500 ng/mL in human whole blood using a 0.05 mL sample volume. NIM811 and the internal standard, d(12)-cyclosporin A (d(12)-CsA), were extracted from blood using MTBE via liquid-liquid extraction. After evaporation of the organic solvent and reconstitution, a 10 microL aliquot of the resulting extract was injected onto the LC-MS/MS system. Chromatographic separation of NIM811 and internal standard was performed using a Waters Symmetry RP-8 (50 x 4.6 mm, 3 microm particle size) column. The mobile phase consists of 10 mm ammonium acetate in water (A) and acetonitrile (B), with 45% B from 0 to 0.2 min, 45 to 85% B from 0.2 to 0.8 min and 85% B from 0.8 to 2.2 min. The total run time was 3.5 min with a flow rate of 0.8 mL/min. The method was validated for sensitivity, linearity, reproducibility, stability, dilution integrity and recovery. The precision and accuracy of quality control samples at low (2.00 ng/mL), medium (20.0 and 400 ng/mL) and high (2000 ng/mL) concentrations were in the range 1.1-4.3% relative standard deviation (RSD) and -2.5-10.0% (bias), respectively, from three validation runs. The method has been used to measure the exposure of NIM811 in human subjects.

Immuno-protective effect of liver on small bowel in combined transplantation of liver and small bowel

AIM: To develop a new combined transplan-tation model of liver and small bowel in rats, and to investigate the protective effect of trans-planted liver on transplanted small bowel.

METHODS: Closed colony Sprague Dawley rats and inbred Wistar rats were included in this study. Five groups were designed: isogene small bowel transplant group (A), isogene liver transplant group (B), xenogene small bowel transplant group (C), xenogene liver transplant group (D), combined transplant of liver and small bowel group (E). Only Wistar rats were used in group A and B, while SD and Wistar rats were used as donors and recipients respectively in group C, D and E. During the combined transplantation of liver and small bowel (CTLS) for the donors, inferior vena cava in chest was cut to construct a muff in the lateral wall of portal vein and cuff was placed. During the operation for the recipients, portal veins of the donors and recipients were connected using cuff technique, and re-arterialization was completed by anastomosing the superior mesenteric artery of graft with the right kidney artery of the recipients. Randomly selected 4 rats from each group were sacrificed on postoperative days (POD) 5, 7 and 14, and grafts were sampled. The rejection of graft was investigated through histopathological analysis, and the apoptosis of the cells of graft were evaluated by TUNEL.

RESULTS: The survival rate of CTLS was 73.3% (22/30). The pathological changes of ischemia and reperfusion injury were observed in group A and B, and the numbers of apoptotic cells in the grafts were decreased with the prolonging of time. However, acute rejection after transplantation appeared in group C and D, and there were more apoptotic cells in the grafts. Mild, moderate and severe acute rejection occurred on POD 5, 7 and 14, respectively in group C, while only mild or severe acute rejection appeared in group E. Furthermore, the number of apoptotic cells in the grafts of group E was markedly decreased on POD 14 in comparison with that of group C (16.9 ± 4.3 vs 20.5 ± 6.3, P < 0.05). The degrees of acute rejection after transplantation and cell apoptosis of the grafts were not significantly different between group D and E.

CONCLUSION: The technique used in this study is feasible for establishment of CTLS model, and the transplanted liver can protect the transplanted intestinal graft from rejection in CTLS.