Cai, Dongqing, Jacquelyne M. Holm, Inga J. Duignan, Jingang Zheng, Munira Xaymardan, Andrew Chin, Victoria L. T. Ballard, Jonathan N. Bella, and Jay M. Edelberg. BDNF-mediated enhancement of inflammation and injury in the aging heart. Physiol Genomics 24: 191-197, 2006. First published December 13, 2005; doi: 10.1152/physiolgenomics.00165.2005.-Aging is associated with shifts in autocrine and paracrine pathways in the cardiac vasculature that may contribute to the risk of cardiovascular disease in older persons. To elucidate the molecular basis of these changes in vivo, phage-display biopanning of 3-and 18-mo-old mouse hearts was performed that identified peptide epitopes with homology to brainderived neurotrophic factor (BDNF) in old but not young phage pools. Quantification of cardiac phage binding by titration and immunostaining after injection with BDNF-like phage identified a twofold increased density of the BDNF receptor, truncated Trk B, in the aging hearts. Studies focused on the receptor ligand using a rat model of transient myocardial ischemia revealed increases in cardiac BDNF associated with local mononuclear infiltrates in 24-but not 4-mo-old rats. To investigate these changes, both 4-and 24-mo-old rat hearts were treated with intramyocardial injections of BDNF (or PBS control), demonstrating significant inflammatory increases with activated macrophage (ED1) in BDNF-treated aging hearts compared with aging controls and similarly treated young hearts. Additional studies with permanent coronary occlusion following intramyocardial growth factor pretreatment revealed that BDNF significantly increased the extent of myocardial injury in older rat hearts (BDNF 35

In this study, we have used two-dimensional electrophoresis, protein sequencing, immunoblotting, and immunohistochemistry to identify proteins that were differentially expressed during aging in human and rat skeletal muscles. Ubiquitin was identified. It was expressed at high levels in old fast-twitch muscles but at low levels in young fast-twitch muscles. It was also discovered that exogenous ubiquitin could suppress the growth of C2C12 cells, in vitro. The reduction in C2C12 cell growth was not attributed to an increase in apoptosis but to an inhibition in cell cycle entry. Furthermore, it was possible to induce muscles to degenerate in vivo by injecting a high dose of exogenous ubiquitin into young healthy skeletal muscles. These results suggest that hyperactivity of the ubiquitin-proteasome pathway is involved in the aging process of fast-twitch muscles. In addition, ubiquitin-dependent growth suppression in satellite cells may be associated with the poor healing potential of old skeletal muscles.

Cai, Dongqing, Munira Xaymardan, Jacquelyne M. Holm, Jingang Zheng, Jorge R. Kizer, and Jay M. Edelberg. Age-associated impairment in TNF-α cardioprotection from myocardial infarction. Am J Physiol Heart Circ Physiol 285: H463-H469, 2003. First published May 8, 2003; 10.1152/ajpheart.00144.2003.—Age-associated dysfunction in cardiac microvascular endothelial cells with impaired induction of cardioprotective platelet-derived growth factor (PDGF)-dependent pathways suggests that alterations in critical vascular receptor(s) may contribute to the increased severity of cardiovascular pathology in older persons. In vivo murine phage-display peptide library biopanning revealed a senescent decrease in cardiac microvascular binding of phage epitopes homologous to tumor necrosis factor-α (TNF-α), suggesting that its receptor(s) may be downregulated in older cardiac endothelial cells. Immunostaining demonstrated that TNF-receptor 1 (TNF-R1) density was significantly lower in the subendocardial endothelium of the aging murine heart. Functional studies confirmed the senescent dysregulation of TNF-receptor pathways, demonstrating that TNF-α induced PDGF-B expression in cardiac microvascular endothelial cells of 4-mo-old, but not 24-mo-old, rats. Moreover, TNF-mediated cardioprotective pathways were impaired in the aging heart. In young rat hearts, injection of TNF-significantly reduced the extent of myocardial injury after coronary ligation: TNF-α, 7.9±1.9% left ventricular injury (n=4) versus PBS, 16.2±7.9% (n=10; P＜0.05). The addition of PDGF-AB did not augment the cardioprotective action of TNF-α. In myocardial infarctions of older hearts, however, TNF- induced significant postcoronary occlusion mortality (TNF-α 80% vs. PBS 0%; n＝10 each, P＜0.05) that was reversed by the coadministration of PDGF-AB. Overall, these studies demonstrate that aging-associated alterations in TNF-α receptor cardiac microvascular pathways may contribute to the increased cardiovasular pathology of the aging heart. Strategies targeted at restoring TNF-α receptor-B mediated expression of PDGF-B may improve cardiac microvascular function and provide novel approaches for treatment and possible prevention of cardiovascular disease in older individuals.

In this study, the protein expression pro

Vascular function in the aging heart is impaired and may underlie the increased morbidity and mortality associated with ischemic heart disease in older individuals. This vascular dysfunction is due, in part, to impairment of plateletderived growth factor (PDGF)-mediated pathways in senescent cardiac microvascular endothelial cells. Restoration of these pathways by intramyocardial injection of growth factor transiently rescues senescent cardiac angiogenesis. Longer-term reconstitution can be achieved experimentally by transplantation of young bone marrow-derived stem cells to promote enescent cardiac angiogenic function in the murine host. Moreover, enhancement of PDGF pathways is cardioprotective, markedly reducing the extent of myocardial injury following coronary occlusion. The clinical translation of these findings for treatment of ischemic heart diseases must overcome the limitation of the proatherosclerotic actions of PDGF, as well as the generation of autologous stem/precursor cell approaches, for the aging cardiovascular system. Strategies targeting growth factor and/or stem-cell homing to gene products downstream of PDGF in the cardiac microvasculature may provide positive feedback loops to enhance cardiac angiogenesis and protection from myocardial infarction and may offer a foundation for developing novel therapies for the prevention and treatment of cardiovascular disease associated with aging.