Browsing by Author "Mapanga, Rudo F."

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    Glycation abolishes the cardioprotective effects of albumin during ex vivo ischemia-reperfusion
    (Wiley Open Access, 2017) Mapanga, Rudo F.; Joseph, Danzil E.; Saieva, Marco; Boyer, Florence; Rondeau, Philippe; Bourdon, Emmanuel; Essop, M. Faadiel
    Hyperglycemia‐induced oxidative stress plays a key role in the onset/progression of cardiovascular diseases. For example, it can trigger formation of advanced glycation end (AGE) products with ischemia‐reperfusion performed under hyperglycemic conditions. For this study, we hypothesized that albumin modified by glycation loses its unique cardioprotective properties in the setting of ischemia‐reperfusion under high glucose conditions. Here, ex vivo rat heart perfusions were performed under simulated normo‐ and hyperglycemic conditions, that is Krebs‐Henseleit buffer containing 11 mmol/L and 33 mmol/L glucose, respectively, ± normal or glycated albumin preparations. The perfusion protocol consisted of a 60 min stabilization step that was followed by 20 min of global ischemia and 60 min reperfusion. Additional experiments were completed to determine infarct sizes in response to 20 min regional ischemia and 120 min reperfusion. At the end of perfusions, heart tissues were isolated and evaluated for activation of the AGE pathway, oxidative stress, and apoptosis. Our data reveal that native bovine serum albumin treatment elicited cardioprotection (improved functional recovery, decreased infarct sizes) under high glucose conditions together with enhanced myocardial antioxidant capacity. However, such protective features are lost with glycation where hearts displayed increased infarct sizes and poor functional recovery versus native albumin treatments. Myocardial antioxidant capacity was also lowered together with activation of the intracellular AGE pathway. These data therefore show that although albumin acts as a cardioprotective agent during ischemia‐reperfusion, it loses its cardioprotective and antioxidant properties when modified by glycation.
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    MuRF2 regulates PPARγ1 activity to protect against diabetic cardiomyopathy and enhance weight gain induced by a high fat diet
    (BioMed Central, 2015) He, Jun; Quintana, Megan T.; Sullivan, Jenyth; Parry, Traci L .; Grevengoed, Trisha J.; Schisler, Jonathan C.; Hill, Joseph A.; Yates, Cecelia C.; Mapanga, Rudo F.; Essop, M. Faadiel; Stansfield, William E.; Bain, James R.; Newgard, Christopher B.; Muehlbauer, Michael J.; Han, Yipin; Clarke, Brian A.; Willis, Monte S.
    Background: In diabetes mellitus the morbidity and mortality of cardiovascular disease is increased and represents an important independent mechanism by which heart disease is exacerbated. The pathogenesis of diabetic cardiomyopathy involves the enhanced activation of PPAR transcription factors, including PPARα, and to a lesser degree PPARβ and PPARγ1. How these transcription factors are regulated in the heart is largely unknown. Recent studies have described post-translational ubiquitination of PPARs as ways in which PPAR activity is inhibited in cancer. However, specific mechanisms in the heart have not previously been described. Recent studies have implicated the musclespecific ubiquitin ligase muscle ring finger-2 (MuRF2) in inhibiting the nuclear transcription factor SRF. Initial studies of MuRF2−/− hearts revealed enhanced PPAR activity, leading to the hypothesis that MuRF2 regulates PPAR activity by post-translational ubiquitination. Methods: MuRF2−/− mice were challenged with a 26-week 60% fat diet designed to simulate obesity-mediated insulin resistance and diabetic cardiomyopathy. Mice were followed by conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1-regulated mRNA expression. Results: MuRF2 protein levels increase ~20% during the development of diabetic cardiomyopathy induced by high fat diet. Compared to littermate wildtype hearts, MuRF2−/− hearts exhibit an exaggerated diabetic cardiomyopathy, characterized by an early onset systolic dysfunction, larger left ventricular mass, and higher heart weight. MuRF2−/− hearts had significantly increased PPARα- and PPARγ1-regulated gene expression by RT-qPCR, consistent with MuRF2’s regulation of these transcription factors in vivo. Mechanistically, MuRF2 mono-ubiquitinated PPARα and PPARγ1 in vitro, consistent with its non-degradatory role in diabetic cardiomyopathy. However, increasing MuRF2:PPARγ1 (>5:1) beyond physiological levels drove poly-ubiquitin-mediated degradation of PPARγ1 in vitro, indicating large MuRF2 increases may lead to PPAR degradation if found in other disease states. Conclusions: Mutations in MuRF2 have been described to contribute to the severity of familial hypertrophic cardiomyopathy. The present study suggests that the lack of MuRF2, as found in these patients, can result in an exaggerated diabetic cardiomyopathy. These studies also identify MuRF2 as the first ubiquitin ligase to regulate cardiac PPARα and PPARγ1 activities in vivo via post-translational modification without degradation.
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    Muscle ring finger-3 protects against diabetic cardiomyopathy induced by a high fat diet
    (BioMed Central, 2015-07) Quintana, Megan T.; He, Jun; Sullivan, Jenyth; Grevengoed, Trisha; Schisler, Jonathan; Han, Yipin; Hill, Joseph A.; Yates, Cecelia C.; Stansfield, William E.; Mapanga, Rudo F.; Essop, M. Faadiel; Muehlbauer, Michael J.; Newgard, Christopher B.; Bain, James R.; Willis, Monte S.
    Background: The pathogenesis of diabetic cardiomyopathy (DCM) involves the enhanced activation of peroxisome proliferator activating receptor (PPAR) transcription factors, including the most prominent isoform in the heart, PPARα. In cancer cells and adipocytes, post-translational modification of PPARs have been identified, including ligand-dependent degradation of PPARs by specific ubiquitin ligases. However, the regulation of PPARs in cardiomyocytes and heart have not previously been identified. We recently identified that muscle ring finger-1 (MuRF1) and MuRF2 differentially inhibit PPAR activities by mono-ubiquitination, leading to the hypothesis that MuRF3 may regulate PPAR activity in vivo to regulate DCM. Methods: MuRF3−/− mice were challenged with 26 weeks 60 % high fat diet to induce insulin resistance and DCM. Conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1 activities were assayed. Results: MuRF3−/− mice exhibited a premature systolic heart failure by 6 weeks high fat diet (vs. 12 weeks in MuRF3+/+). MuRF3−/− mice weighed significantly less than sibling-matched wildtype mice after 26 weeks HFD. These differences may be largely due to resistance to fat accumulation, as MRI analysis revealed MuRF3−/− mice had significantly less fat mass, but not lean body mass. In vitro ubiquitination assays identified MuRF3 mono-ubiquitinated PPARα and PPARγ1, but not PPARβ. Conclusions: These findings suggest that MuRF3 helps stabilize cardiac PPARα and PPARγ1 in vivo to support resistance to the development of DCM. MuRF3 also plays an unexpected role in regulating fat storage despite being found only in striated muscle.
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    Oleanolic acid : a novel cardioprotective agent that blunts hyperglycemia-induced contractile dysfunction
    (Public Library of Science, 2012-10-16) Mapanga, Rudo F.; Rajamani, Uthra; Dlamini, Nonkululeko; Zungu-Edmondson, Makhosazane; Kelly-Laubscher, Roison; Shafiullah, Mohammed; Wahab, Athiq; Hasan, Mohamed Y.; Fahim, Mohamed A.; Rondeau, Phillipe; Bourdon, Emmanuel; Essop, M. Faadiel
    Diabetes constitutes a major health challenge. Since cardiovascular complications are common in diabetic patients this will further increase the overall burden of disease. Furthermore, stress-induced hyperglycemia in non-diabetic patients with acute myocardial infarction is associated with higher in-hospital mortality. Previous studies implicate oxidative stress, excessive flux through the hexosamine biosynthetic pathway (HBP) and a dysfunctional ubiquitin-proteasome system (UPS) as potential mediators of this process. Since oleanolic acid (OA; a clove extract) possesses antioxidant properties, we hypothesized that it attenuates acute and chronic hyperglycemia-mediated pathophysiologic molecular events (oxidative stress, apoptosis, HBP, UPS) and thereby improves contractile function in response to ischemia-reperfusion. We employed several experimental systems: 1) H9c2 cardiac myoblasts were exposed to 33 mM glucose for 48 hr vs. controls (5 mM glucose); and subsequently treated with two OA doses (20 and 50 mM) for 6 and 24 hr, respectively; 2) Isolated rat hearts were perfused ex vivo with Krebs-Henseleit buffer containing 33 mM glucose vs. controls (11 mM glucose) for 60 min, followed by 20 min global ischemia and 60 min reperfusion 6 OA treatment; 3) In vivo coronary ligations were performed on streptozotocin treated rats 6 OA administration during reperfusion; and 4) Effects of long-term OA treatment (2 weeks) on heart function was assessed in streptozotocin-treated rats. Our data demonstrate that OA treatment blunted high glucose-induced oxidative stress and apoptosis in heart cells. OA therapy also resulted in cardioprotection, i.e. for ex vivo and in vivo rat hearts exposed to ischemia-reperfusion under hyperglycemic conditions. In parallel, we found decreased oxidative stress, apoptosis, HBP flux and proteasomal activity following ischemia-reperfusion. Long-term OA treatment also improved heart function in streptozotocin-diabetic rats. These findings are promising since it may eventually result in novel therapeutic interventions to treat acute hyperglycemia (in non-diabetic patients) and diabetic patients with associatedcardiovascular complications.
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    Partial inhibition of the ubiquitin– proteasome system ameliorates cardiac dysfunction following ischemia–reperfusion in the presence of high glucose
    (Springer Verlag, 2015) Adams, Buin; Mapanga, Rudo F.; Essop, M. Faadiel; Physiological Sciences
    Abstract Background: Acute hyperglycemia co-presenting with myocardial infarction (in diabetic and non-diabetic individuals) is often associated with a poor prognosis. Although acute hyperglycemia induces oxidative stress that can lead to dysregulation of the ubiquitin–proteasome system (UPS), it is unclear whether increased/decreased UPS is detrimental with ischemia–reperfusion under such conditions. As our earlier data implicated the UPS in cardiac damage, we hypothesized that its inhibition results in cardioprotection with ischemia–reperfusion performed under conditions that simulate acute hyperglycemia. Methods: Ex vivo rat heart perfusions were performed with Krebs–Henseleit buffer containing 33 mM glucose vs. controls (11 mM glucose) for 60 min stabilization, followed by 20 min global ischemia and 60 min reperfusion ± 5 µM lactacystin and 10 µM MG-132, respectively. The UPS inhibitors were added during the first 20 min of the reperfusion phase and various cardiac functional parameters evaluated. In parallel experiments, infarct sizes were assessed following 20 min regional ischemia and 120 min reperfusion ± each of the respective UPS inhibitors (added during reperfusion). Heart tissues were collected and analyzed for markers of oxidative stress, UPS activation, inflammation and autophagy. Results: The proteasome inhibitor doses and treatment duration here employed resulted in partial UPS inhibition during the reperfusion phase. Both lactacystin and MG-132 administration resulted in cardioprotection in our experimental system, with MG-132 showing a greater effect. The proteasome inhibitors also enhanced cardiac superoxide dismutase protein levels (SOD1, SOD2), attenuated pro-inflammatory effects and caused an upregulation of autophagic markers. Conclusions: This study established that partial proteasome inhibition elicits cardioprotection in hearts exposed to ischemia–reperfusion with acute simulated hyperglycemia. These data reveal that protease inhibition triggered three major protective effects, i.e. (a) enhancing myocardial anti-oxidant defenses, (b) attenuating inflammation, and (c) increasing the autophagic response. Thus the UPS emerges as a unique therapeutic target for the treatment of ischemic heart disease under such conditions. Keywords: Ubiquitin–proteasome system, Ischemia–reperfusion, Cardiac dysfunction, Hyperglycemia, Inflammation, Oxidative stress, Autophagy
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    Resveratrol co-treatment attenuates the effects of HIV protease inhibitors on rat body weight and enhances cardiac mitochondrial respiration
    (Public Library of Science, 2017-01-20) Symington, Burger; Mapanga, Rudo F.; Norton, Gavin R.; Essop, M. Faadiel
    Since the early 1990s human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) emerged as a global health pandemic, with sub-Saharan Africa the hardest hit. While the successful roll-out of antiretroviral (ARV) therapy provided significant relief to HIV-positive individuals, such treatment can also elicit damaging side-effects. Here especially HIV protease inhibitors (PIs) are implicated in the onset of cardio-metabolic complications such as type-2 diabetes and coronary heart disease. As there is a paucity of data regarding suitable co-treatments within this context, this preclinical study investigated whether resveratrol (RSV), aspirin (ASP) or vitamin C (VitC) co-treatment is able to blunt side-effects in a rat model of chronic PI exposure (Lopinavir/Ritonavir treatment for 4 months). Body weights and weight gain, blood metabolite levels (total cholesterol, HDL, LDL, triglycerides), echocardiography and cardiac mitochondrial respiration were assessed in PI-treated rats ± various co-treatments. Our data reveal that PI treatment significantly lowered body weight and cardiac respiratory function while no significant changes were found for heart function and blood metabolite levels. Moreover, all co-treatments ameliorated the PI-induced decrease in body weight after 4 months of PI treatment, while RSV co-treatment enhanced cardiac mitochondrial respiratory capacity in PI-treated rats. This pilot study therefore provides novel hypotheses regarding RSV co-treatment that should be further assessed in greater detail.