Mechanisms of phospholamban dysregulation in anthrax lethal toxin-induced diastolic heart failure : a dissertation /
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| Format: | Thesis Book |
| Language: | English |
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[College Station, Texas :
Texas A&M University System Health Science Center,
2010].
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| Subjects: |
| Abstract: | ABSTRACT: We previously demonstrated that anthrax lethal toxin (LT, protective antigen [PA] + lethal factor [LF] ) produces acute systolic heart failure in male Sprague-Dawley (SD) rats. We tested whether the LT-mediated loss in cardiac function is a consequence of dysregulated signaling mechanisms resulting from LF-mediated MEK cleavage. A bolus iv injection of LT (0.02 mg PA + 0.01 mg LF) administered to adult male SD rats in a time course (2, 4, 8 and 24 h) study of LT toxicity revealed acute diastolic dysfunction via diminished mitral flow velocities for early diastolic filling at 4 and 8 h post-LT (P<0.01 and p<0.05, respectively), pulmonary regurgitation and left atrial dilation. Biochemical analysis of LV tissue revealed PLB dephosphorylation at 2-8 h (p<0.001), although PKA activity was increased at all time-points post-LT (p<0.01). Additionally, PP2A enzymatic activities were increased at 2-8 h compared to controls (p<0.01), suggesting that LT induces dephosphorylation of PLB at 2-4 h through PP2A. LT dose-response effects on isolated neonatal rat ventricular myocytes (NRVM) revealed increased B56[alpha] total protein, at a dose of 0.05 ng/mL PA + 0.025 ng/mL LF, accompanied by diminished PLB and JNK phosphorylation. Using this dose for time course experiments, LT treatment resulted in diminished activation of JNK from 1 h to 4 h (p<0.05). Akt phosphorylation at both Thr³⁰⁸ and Ser⁴⁷³ were also significantly reduced (p<0.001 and p<0.01, respectively) from 30 min to 4 h, accompanied by elevated B56[alpha] total protein and intracellular Ca²⁺, and reduced PLB phosphorylation. To determine whether JNK regulates PP2A activity, gain-of-function and loss-of-function studies performed with regard to MEK7, JNK1 and JNK2 revealed a significant role for JNK1 in PP2A-mediated Ca²⁺ dysregulation. Since Akt has recently been shown to directly phosphorylate PLB at Thr¹⁷, we employed adenoviral-mediated gene therapy of Akt targeted to the sarcoplasmic reticulum (SR) as a strategy to phosphorylate, and thus inactivate, PLB. Compared to the virus control, the SR-targeted Akt adenoviral construct protected against elevated intracellular Ca²⁺ levels during 2 h LT intoxication. The present study suggests a primary role of anthrax LT in cardiac dysfunction through dysregulation of signaling mechanisms that modulate myocyte SR Ca²⁺ mobilization. |
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| Item Description: | Vita. "Major Subject: Medical Sciences". "Submitted to the Office of Research and Graduate Studies of The Texas A&M University System Health Science Center in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2010" Approved as to style and content by: David E. Dostal, Cynthia Meininger, Alejandro Arroliga, Linley E. Watson, Avadhesh Sharma |
| Physical Description: | ix, 125 leaves : illustrations (mostly color) ; 28 cm. |
| Bibliography: | Includes bibliographical references (leaves 95-120). |