AdvisorWatson, Ronald R.
Committee ChairWatson, Ronald R.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractRecent studies support the association between metabolic syndrome (MetS), a cluster of cardiovascular risk factors, and diastolic dysfunction. Disproportionate collagen accumulation, particularly cross-linking of collagen, plays a key role in translating interstitial fibrosis into mechanical chamber stiffness and diastolic dysfunction. Characteristic changes in the expression and activity of myocardial lysyl oxidase (LOX), a matrix modifying enzyme that catalyzes cross-linked collagen, are unclear in MetS. We established a diet-induced MetS model to study diastolic dysfunction by treating male C57BL/6 mice a high-fat high-simple carbohydrate (HFHSC) diet for 6 months. Despite blunted gene expression of LOX isoforms, MetS mice demonstrated significant increase in the ratio of protein expression of mature to proenzyme LOX, enhanced LOX activity, and increased cardiac cross-linked collagen compared with controls. This fibrotic response coincided with marked increase in left ventricular end-diastolic pressure and stiffness and impaired diastolic filling pattern. Our data demonstrate that diet-induced MetS alters the remodeling enzyme LOX, thereby increasing the amount of crosslinking and inducing diastolic dysfunction.Furthermore we examined the role of T-lymphocytes in myocardial LOX regulation in diet-induced fibrotic hearts. Female SCID mice which are devoid of functional T-lymphocytes and C57BL/6 mice were treated with HFHSC diet for 12 months. Similar to male C67BL/6, female HFHSC-fed C57BL/6 mice demonstrated significant increase in maturation and catalytic activity of myocardial LOX, cross-linking, ventricular stiffness and diastolic dysfunction. Whereas induction of LOX protein was minimal in SCID mice compared with wild-type counterparts. Correspondingly fibrillar cross-linked collagen formation and diastolic dysfunction were less prominent in SCID mice. Our results suggest a potential role of T-lymphocytes in induction of myocardial stiffness and diastolic dysfunction through modulation of LOX-dependent collagen maturation.Moreover we studied the role of leptin, an adipokine over-produced in MetS with fibrotic effects in non-cardiac tissues, as a key mediator of profibrogenic responses in the heart by administrating leptin to C57BL/6 and leptin-deficient ob/ob mice. With exogenous leptin administration ob/ob mice displayed passive diastolic filling dysfunction that coincided with increase in myocardial collagen compared with ob/ob controls. Our findings suggest profibrotic effects of leptin in the heart, primarily through predominance of collagen synthesis over degradation.
Degree ProgramNutritional Sciences