Loss of interstitial collagen causes structural and functional alterations of cardiomyocyte subsarcolemmal mitochondria in acute volume overload

Abstract

Volume overload (VO) caused by aortocaval fistula (ACF) is associated with oxidative/inflammatory stress. The resulting inflammation, matrix metalloproteinase (MMP) activation, and collagen degradation is thought to play a pivotal role in left ventricular (LV) dilatation and failure. Since mitochondria are also targets for inflammation and oxidative stress, we hypothesized that there would be bioenergetic dysfunction with acute VO. In Sprague-Dawley rats subjected to 24 hrs of ACF, there was a two-fold increase in LV pressure-volume area in vivo, consistent with increased LV myocardial oxygen usage and increased bioenergetic demand in cardiomyocytes. Isolated cardiomyocytes from ACF LVs demonstrated increased hydrogen peroxide and superoxide formation and increased MMP activity. Subsarcolemmal mitochondria (SSM) showed a 40% decrease in state 3 respiration and proteomic analysis of SSM demonstrated decreased levels of complexes I-V in ACF. Immunohistochemical analysis revealed disruption of the subsarcolemmal location of the SSM network in ACF. To test for a potential link between SSM dysfunction and loss of interstitial collagen, rats were treated with the MMP-inhibitor PD166793 prior to ACF. MMP-inhibitor preserved interstitial collagen, integrin-α5 and the SSM structural arrangement. In addition, the decrease in state 3 mitochondrial respiration with ACF was prevented by PD166793. These studies established an important interaction between degradation of interstitial collagen in acute VO and the disruption of SSM structure and function which could contribute to progression to heart failure.

Xanthine oxidase inhibition preserves left ventricular systolic but not diastolic function in cardiac volume overload

“…5, A and B), suggesting that this could be a possible mechanism of increased mitochondrial Ca 2ϩ uptake (29,39), and this effect was not blunted by the addition of allopurinol to the ACF group. Since XO has been shown to be increased in VO, we decided to determine if the protein levels of MnSOD were altered as a compensatory mechanism to cope with increased levels of ROS, specifically O 2 ·Ϫ .…”

“…Sprague-Dawley rats (200 -250g) at 12 wk of age were subjected to either to sham or ACF, as previously described by our laboratory (18,33,39,40), with and without the XO inhibitor allopurinol (100 mg/kg, Sigma) for 8 wk. Allopurinol was started at the time of surgery and delivered in standard rat chow.…”

“…Cardiomyocytes were isolated from sham and ACF rats, as previously described by our laboratory (18,33,39). Briefly, hearts were perfused with perfusion buffer (120 mmol/l NaCl, 15 mmol/l KCl, 0.5 mmol/l KH 2PO4, 5 mmol/l NaHCO3, 10 mmol/l HEPES, and 5 mmol/l glucose at pH 7.0) for 5 min and digested with perfusion buffer containing 2% collagenase type II (Invitrogen, Carlsbad, CA) for 30 min at 37°C.…”

“…Recently, our laboratory has demonstrated increased cardiomyocyte oxidative stress in patients with VO of isolated chronic mitral regurgitation (1) and in rats with VO of aortocaval fistula (ACF) (18,39). Specifically, xanthine oxidase (XO) is elevated in cardiomyocytes along with myofibrillar degeneration and mitochondrial dysfunction and damage, despite a preserved LV ejection fraction (LVEF).…”

The extracellular matrix in myocardial injury, repair, and remodeling

“…Volume overload is associated with a distinct profile of changes in the composition of the ECM that ultimately lead to chamber dilation and contribute to systolic dysfunction. In contrast to the marked accentuation in collagen deposition triggered by a pressure load, volume overload is associated with a reduction in interstitial collagen content due to increased MMP expression (113)(114)(115) and augmented autophagic degradation of procollagen in cardiac fibroblasts (116). Pharmacologic inhibition studies suggested that MMP activation is directly implicated in dilative remodeling of the volume-overloaded ventricle (117), but the mechanisms responsible for the distinct cell biological changes and matrix alterations in volume overload remain poorly understood.…”