Thesis (M. Phil.)--University of Queensland, 2002. / Includes bibliographical references.

Ischaemic stroke rates are expected to rise significantly in the next decades due to an aging population. This increases the demand for new stroke biomarkers for early detection of patients at risk and new targets for treatment. It has been hypothesized that epigenetics may be important in the aetiology of stroke. The study consisted of three types of investigation: analysis of candidate gene polymorphism, candidate gene methylation analysis and epigenome-wide methylation analysis (EWAS) of pooled stroke and control samples. The stroke types studied were large vessel disease (LVD), small vessel disease (SVD) and cardioembolic stroke (CE). DNA from peripheral blood samples was used for EWAS and methylation analysis. Significant increases in rare allele frequency were observed in the EHMT2 and DNMT3B genes for all stroke cases; MBD2, DNMT3B and DNMT3L polymorphisms were associated with LVD. IL10, SOD3, LINE1 and PITX2 were significantly hypomethylated in LVD. IL10 and ALOX15 were hypomethylated in CE compared to controls. Methylation levels of following genes were associated with age (LINE1, IL10, MTHFR, TNFα, and PITX2), gender (SOD3 and LINE1), total cholesterol level (SOD3) and systolic blood pressure (IL10). HDAC9 genetic polymorphism was associated with the MTHFR methylation level. A distinctive methylation pattern for each stroke subtype was found by EWAS. The CE pool was hypomethylated at genome, chromosome and gene level, while LVD and SVD pools had regions with higher and lower methylation levels compared to the controls. GNAS was identified as new candidate gene by EWAS. The results suggested that genetic polymorphism and DNA methylation levels of candidate genes were associated with ischaemic stroke. Stroke subtypes had distinct methylation profiles suggesting differences in underlying aetiology. Variations in methylation levels detected in this study could lead to identification of specific biomarkers. Replication on a large number of subjects is required before final conclusions can be drawn.

Heart transplantation is often the only therapeutic option for patients with end stage heart disease. Allograft organs are in short supply. Thus, preserving the life of a grafted organ is extremely important. Cardiac allograft vasculopathy (CAV) is an expression of chronic rejection that accounts for the greatest loss of graft function in transplanted hearts. Peri-transplant ischemia/reperfusion (I/R)-injury occurs during transplantation when blood flow is stopped to remove the heart from the donor and then is reinstated upon implantation of the donor heart into the recipient. This oxidative injury contributes to vascular dysfunction and CAV. In this dissertation, I hypothesize that prevention and/or reduction of I/R during transplantation reduces post-transplant vascular dysfunction and CAV. In this regard, myself and my colleagues examined the roles of apoptosis repressor with caspase recruitment domain (ARC) and cytochrome p450 (CYP) 2C enzymes in UR-induced vascular dysfunction and CAV. ARC expression was detected in endothelial cells (ECs) and smooth muscle cells (SMCs); however, increased levels of ARC do not protect against oxidant injury. ARC overexpression did protect against oxidant-induced cell death in H9c2 rat embryonic myoblasts. We observed that ARC-overexpression prevented H9c2 differentiation into muscle cells. With our focus on vascular injury, we turned our attention to the CYP 2C enzymes. Both endothelium-dependent and independent vascular function was impaired following I/R. Pre-treatment with the CYP 2C inhibitor sulfaphenazole (SP) restored endothelial sensitivity to acetylcholine, but did not restore sensitivity to endothelium-independent vasodilators. Rat heterotopic heart transplants were performed with rats being treated with SP or vector control prior to surgery. Rats treated with SP showed significantly reduced luminal narrowing and had decreased SMC proliferation, oxidant and interferon-y levels. No differences were detected in immune infiltration or apoptosis. Complementary studies in cultured vascular cells revealed that CYP 2C9 expression decreased viability and increased ROS production following hypoxia and re-oxygenation in ECs but not in SMCs. In summary, we did not detect protection of vascular cells by ARC, but did discover a novel role for ARC in differentiation. CYP 2C contributes to post-ischemic vascular dysfunction and CAV through increased oxidative stress and endothelial dysfunction.

The BNIP3 family, a group of death-inducing mitochondrial proteins, includes BNIP3, NIX and BNIP3h. These proteins share structural and functional similarities. BNIP3 causes neuronal cell death in a necrosis-like, caspase-independent manner with mitochondrial dysfunction. We reported that BNIP3 plays a role in delayed neuronal death in stroke models. Over-expression of BNIP3 causes up to 70% neuronal death, while knockdown of BNIP3 only protects 23% neurons from hypoxia. Thus, we hypothesize that other members of the BNIP3 subfamily compensate for the loss of BNIP3. BNIP3 and NIX were highly upregulated in the oxygen and glucose deprivation (OGD)/reoxygenation model, and knockdown of BNIP3 or NIX protected about 20% - 44% of neurons. Knockdown of BNIP3 family reduced neuronal death by 48%. Mitochondrial membrane potential loss, mitochondrial permeability transition pore (MPTP) opening and reactive oxygen species (ROS) production were all significantly attenuated by BNIP3 and/or NIX inhibition. AIF and EndoG were reported involving in caspase-independent cell death in ischemic stroke. We found that AIF was released from mitochondria and translocated into nuclei in neurons after OGD/reoxygenation, while inhibition of BNIP3 blocked AIF and EndoG translocation and prevented neuronal death. Over-expression of BNIP3 and NIX caused AIF translocation and subsequent neuronal death. These data reveal the effects of the BNIP3 family in neuronal death and indicate that AIF and EndoG are two downstream factors in the BNIP3-mediated cell death pathway. Meanwhile, necrostatin-1 (Nec-1), an inhibitor for a caspase-independent necrotic cell death, is able to protect neurons from death in stroke, mechanism of which is unclear. Here, we confirmed that Nec-1 significantly increased survival of neurons in models of stroke in vivo and in vitro. It also attenuated hypoxia or BNIP3-induced mitochondrial dysfunction and prevented mitochondrial release of AIF. Nec-1 did not affect the expression levels of BNIP3 but prevented its integration into mitochondria. These results suggest that Nec-1 protects neurons against ischemia by targeting BNIP3. In summary, this research indicates that the BNIP3 family is one of the regulators of caspase-independent neuronal death in stroke and that Nec-1 is an inhibitor for BNIP3 and a potential therapeutic agent for stroke.

Neuronal vulnerability to ischemia is dependent on the balance between pro-survival and pro-death cellular signaling. In the latter, it is increasingly appreciated that toxic Ca2+ influx can occur not only via postsynaptic glutamate receptors, but also through other cation conductances. One such conductance, the Transient receptor potential melastatin type-2 (TRPM2) channel, is a non-specific cation channel having similar homology to TRPM7, a conductance reported to play a key role in anoxic neuronal death. The role of TRPM2 conductances in ischemic Ca2+ influx has been difficult to study due to the lack of specific modulators. Here we used TRPM2-null mice (TRPM2(-/-)) to study how TRPM2 may modulate neuronal vulnerability to ischemia. TRPM2(-/-) mice subjected to transient middle cerebral artery occlusion (tMCAO) exhibited smaller infarcts when compared to wild-type (WT) animals, suggesting the absence of TRPM2 to be protective. Surprisingly, field potentials (fEPSPs) recorded during oxidative stress in brain slices taken from TRPM2(-/-) mice revealed increased excitability, a phenomenon normally associated with ischemic vulnerability, whereas WT fEPSPs were unaffected. The upregulation in fEPSP in TRPM2(-/-) neurons was blocked selectively by an NR2A antagonist. This oxidative stress-induced increase in excitability of TRPM2(-/-) fEPSPs depended on the upregulation and downregulation of NR2A and NR2B-containing NMDARs, respectively, and augmented pro-survival signaling via Akt and ERK pathways culminating in the inhibition of the proapoptotic factor, GSK3β. Cultured hippocampal neurons from TRPM2(-/-) animals subjected to oxygen glucose deprivation had a reduction in cell death in comparison to WT neurons, demonstrating that absence of TRPM2 is protective at the neuronal level in vitro. Our results suggest that TRPM2 plays a role in downregulating pro-survival signals in central neurons and that TRPM2 channels may comprise a therapeutic target for preventing ischemic damage.

The BNIP3 family, a group of death-inducing mitochondrial proteins, includes BNIP3, NIX and BNIP3h. These proteins share structural and functional similarities. BNIP3 causes neuronal cell death in a necrosis-like, caspase-independent manner with mitochondrial dysfunction. We reported that BNIP3 plays a role in delayed neuronal death in stroke models. Over-expression of BNIP3 causes up to 70% neuronal death, while knockdown of BNIP3 only protects 23% neurons from hypoxia. Thus, we hypothesize that other members of the BNIP3 subfamily compensate for the loss of BNIP3. BNIP3 and NIX were highly upregulated in the oxygen and glucose deprivation (OGD)/reoxygenation model, and knockdown of BNIP3 or NIX protected about 20% - 44% of neurons. Knockdown of BNIP3 family reduced neuronal death by 48%. Mitochondrial membrane potential loss, mitochondrial permeability transition pore (MPTP) opening and reactive oxygen species (ROS) production were all significantly attenuated by BNIP3 and/or NIX inhibition. AIF and EndoG were reported involving in caspase-independent cell death in ischemic stroke. We found that AIF was released from mitochondria and translocated into nuclei in neurons after OGD/reoxygenation, while inhibition of BNIP3 blocked AIF and EndoG translocation and prevented neuronal death. Over-expression of BNIP3 and NIX caused AIF translocation and subsequent neuronal death. These data reveal the effects of the BNIP3 family in neuronal death and indicate that AIF and EndoG are two downstream factors in the BNIP3-mediated cell death pathway. Meanwhile, necrostatin-1 (Nec-1), an inhibitor for a caspase-independent necrotic cell death, is able to protect neurons from death in stroke, mechanism of which is unclear. Here, we confirmed that Nec-1 significantly increased survival of neurons in models of stroke in vivo and in vitro. It also attenuated hypoxia or BNIP3-induced mitochondrial dysfunction and prevented mitochondrial release of AIF. Nec-1 did not affect the expression levels of BNIP3 but prevented its integration into mitochondria. These results suggest that Nec-1 protects neurons against ischemia by targeting BNIP3. In summary, this research indicates that the BNIP3 family is one of the regulators of caspase-independent neuronal death in stroke and that Nec-1 is an inhibitor for BNIP3 and a potential therapeutic agent for stroke.

Kidney transplants from both living-related (LRD) and living unrelated (LURD) donors have superior function and survival than transplants from cadaver donors. This may be unsurprising as kidneys from living donors are procured under optimal conditions, from healthy donors with minimal ischaemia times. In contrast, cadaver kidneys are obtained from traumatised donors and may experience extended periods of cold ischaemic storage before transplantation. An immunohistochemical analysis has been performed on biopsies obtained before, and immediately after transplantation, to investigate the potential causes of early inflammatory events associated with cadaver renal transplantation that may influence subsequent graft outcome. An immunohistochemical analysis of biopsies obtained before transplantation demonstrated upregulated expression of endothelial E-selectin and proximal tubular expression of ICAM-1, VCAM-1 and HLA Class II antigens in cadaver donor kidneys. Analysis of donor parameters demonstrated that traumatic physiological events experienced in intensive care around the time of brain death were significantly associated with the induction of proinflammatory antigens. Antigen induction in cadaver donor kidneys before transplantation was significantly associated with early acute rejection. Furthermore, in cadaveric kidneys with long cold ischaemia times, glomerular neutrophil infiltration and deposition of activated platelets expressing P-selectin on intertubular capillaries were detected following reperfusion, in association with impaired short and long term graft function. Expression of inflammatory mediators were absent in all LRD renal allografts before and after reperfusion. A clinical trial was performed to determine whether ischaemia/reperfusion injury may be ameliorated by reflushing cadaver kidneys after cold storage to remove harmful products that may have accumulated in the vessel lumen. Reflushing did not prevent the inflammatory events observed after reperfusion or improve graft function. Therefore, a novel, oxygen free radical scavenger (lec-SOD) was obtained to assess its potential efficacy in preventing ischaemia/reperfusion injury. Lec-SOD bound with high affinity to macro- and microvascular endothelial cells under cold hypoxic conditions following incorporation into Marshall's preservation solution, significantly inhibiting cold hypoxia induced cell death, adhesion molecule induction and neutrophil adhesion. Furthermore, preservation of kidneys with lec- SOD for 18 hr in an experimental model of chronic renal allograft rejection, significantly attenuated neutrophil infiltration and MHC Class I induction day 1 post-transplant, with improved long term renal function. The results presented in this Thesis demonstrate that donor factors and cold ischaemia/ reperfusion injury elicit an early inflammatory response that may influence graft outcome of cadaver kidneys. Refinements in donor management and organ preservation may limit the deleterious effects of ischaemia/reperfusion injury in cadaver renal allografts, increasing graft survival to that observed in living donor transplantation.

The two of major pathways that cause ischemic damage are oxidative stress and inflammation. To decreasing oxidative stress and inflammation, new anti-oxidant and anti-inflammatory agents are tested in ischemic models. In order to study ALRX828C anti-inflammatory properties, an in vivo six-day old air pouch model of inflammation was used to evaluate the anti-inflammatory potential of ALRX828C. Also, the dose response of ALRX828C for TNFα (IC50 = 30 μM) and IL-17 (IC50 = 1.3 μM) were determined by using human peripheral blood mononuclear cell cultures stimulated with ionomycin and PMA. To examine ALRX828C anti-inflammatory effect in neuroinflammation, a neurodegenerative model was used to evaluate its potential. I also showed that reducing oxidative stress with a potent antioxidant, Idebenone in nano-emulsion form, can effectively reduce tissue damage during ischemia in organotypic slice culture subjected to oxygen-glucose depravation (OGD). In conclusion, reducing oxidative stress and inflammation after stroke can reduce ischemic damage substantially.

Cardioprotective effects of glucagon-like peptide-1 (GLP-1), the GLP-1 receptor (GLP-1R) agonist exendin-4 (Ex-4), and GLP-1(9-36), a cleavage product of GLP-1, were examined in ischemia-reperfusion (I/R) models of both isolated mouse hearts and cultured cardiac myocytes (CMs) using both wild-type (WT) and GLP-1R knockout (Glp1r-/-) mice. In WT hearts, GLP-1 and Ex-4 significantly improved left ventricular functional recovery vs. untreated controls following I/R, whether the drugs were administered prior to ischemia (pre-ischemia) or during reperfusion (post-ischemia). Surprisingly, the cardioprotective effects of pre- and post-ischemia treatments with GLP-1, but not Ex-4, remained evident in Glp1r-/- hearts. Although pre-ischemia infusion of GLP-1(9-36) induced lower functional recovery than untreated controls, post-ishemia infusion of GLP-1(9-36) augmented functional recovery and reduced infarct size to a similar extent to that of GLP-1 and Ex-4 in hearts from both WT and Glp1r-/- mice. Mass spectrometry was used to assay conversion of GLP-1 to GLP-1(9-36) in coronary effluents of isolated mouse hearts. Within 15 min of infusing GLP-1, significant amounts of GLP-1(9-36) were generated by the heart. By 30 min, only trace amounts of intact GLP-1 remained in coronary effluents indicating the heart rapidly converts GLP-1 to GLP-1(9-36). In CMs undergoing simulated I/R injury in vitro, both GLP-1(9-36) and Ex-4 significantly improved cell viability, LDH release and caspase-3 activation. These effects were significantly attenuated by co-treatments with LY294002, PD98059 and Ex(9-39), inhibitors of PI3K, ERK1/2, and GLP-1R respectively. The actions of Ex-4, but not GLP-1(9-36), were lost in CMs isolated from Glp1r-/- mice and only GLP-1(9-36), but not Ex-4, improved the survival of human aortic endothelial cells (HAEC) undergoing simulated I/R injury. Of note, both GLP-1 and GLP-1(9-36) treatments also demonstrated potent vasodilatory effects, as manifested by increased coronary flow rates in isolated hearts and increased diameters of pre-constricted mesenteric arteries isolated from both WT and Glp1r-/- mice. The cardioprotective effects on isolated hearts and vasodilatory effects on isolated mesenteric arteries, induced by GLP-1 was blunted by co-treatment with a dipeptidyl peptidase-4 (DPP-4) enzyme inhibitor known to block conversion of GLP-1 to GLP-1(9-36). Together, these data suggest that the beneficial effects of GLP-1 in I/R injury are mediated in part by GLP(9-36) and support the existence of a GLP-1(9-36) responsive, but Ex(9-39)-sensitive cardioprotective signaling pathway distinct from that associated with the classical GLP-1R.

The two of major pathways that cause ischemic damage are oxidative stress and inflammation. To decreasing oxidative stress and inflammation, new anti-oxidant and anti-inflammatory agents are tested in ischemic models. In order to study ALRX828C anti-inflammatory properties, an in vivo six-day old air pouch model of inflammation was used to evaluate the anti-inflammatory potential of ALRX828C. Also, the dose response of ALRX828C for TNFα (IC50 = 30 μM) and IL-17 (IC50 = 1.3 μM) were determined by using human peripheral blood mononuclear cell cultures stimulated with ionomycin and PMA. To examine ALRX828C anti-inflammatory effect in neuroinflammation, a neurodegenerative model was used to evaluate its potential. I also showed that reducing oxidative stress with a potent antioxidant, Idebenone in nano-emulsion form, can effectively reduce tissue damage during ischemia in organotypic slice culture subjected to oxygen-glucose depravation (OGD). In conclusion, reducing oxidative stress and inflammation after stroke can reduce ischemic damage substantially.