The goal of this study was to interrogate the role of inducible NO synthase (iNOS) in the late phase of ischemic preconditioning (PC) in vivo. A total of 321 mice were used. Wild-type mice preconditioned 24 h earlier with six cycles of 4-min coronary occlusion͞4-min reperfusion exhibited a significant (P < 0.05) increase in myocardial iNOS protein content, iNOS activity (assessed as calciumindependent L-citrulline formation), and nitrite ؉ nitrate tissue levels. In contrast, endothelial NOS protein content and calcium-dependent NOS activity remained unchanged. No immunoreactive neuronal NOS was detected. When wild-type mice were preconditioned 24 h earlier with six 4-min occlusion͞4-min reperfusion cycles, the size of the infarcts produced by a 30-min coronary occlusion followed by 24 h of reperfusion was reduced markedly (by 67%; P < 0.05) compared with sham-preconditioned controls, indicating a late PC effect. In contrast, when mice homozygous for a null iNOS allele were preconditioned 24 h earlier with the same protocol, infarct size was not reduced. Disruption of the iNOS gene had no effect on early PC or on infarct size in the absence of PC. These results demonstrate that (i) the late phase of ischemic PC is associated with selective up-regulation of iNOS, and (ii) targeted disruption of the iNOS gene completely abrogates the infarct-sparing effect of late PC (but not of early PC), providing unequivocal molecular genetic evidence for an obligatory role of iNOS in the cardioprotection afforded by the late phase of ischemic PC. Thus, this study identifies a specific protein that mediates late PC in vivo.

Following myocardial infarction, nonischemic myocyte death results in infarct expansion, myocardial loss, and ventricular dysfunction. Here, we demonstrate that a specific proapoptotic gene, Bnip3, minimizes ventricular remodeling in the mouse, despite having no effect on early or late infarct size. We evaluated the effects of ablating Bnip3 on cardiomyocyte death, infarct size, and ventricular remodeling after surgical ischemia/reperfusion (IR) injury in mice. Immediately following IR, no significant differences were observed between Bnip3(-/-) and WT mice. However, at 2 days after IR, apoptosis was diminished in Bnip3(-/-) periinfarct and remote myocardium, and at 3 weeks after IR, Bnip3(-/-) mice exhibited preserved LV systolic performance, diminished LV dilation, and decreased ventricular sphericalization. These results suggest myocardial salvage by inhibition of apoptosis. Forced cardiac expression of Bnip3 increased cardiomyocyte apoptosis in unstressed mice, causing progressive LV dilation and diminished systolic function. Conditional Bnip3 overexpression prior to coronary ligation increased apoptosis and infarct size. These studies identify postischemic apoptosis by myocardial Bnip3 as a major determinant of ventricular remodeling in the infarcted heart, suggesting that Bnip3 may be an attractive therapeutic target.

Background-Heat-shock proteins (Hsps) have been shown to render cardioprotection from stress-induced injury; however, little is known about the role of another small heat-shock protein, Hsp20, which regulates activities of vasodilation and platelet aggregation, in cardioprotection against ischemia injury. We recently reported that increased expression of Hsp20 in cardiomyocytes was associated with improved contraction and protection against ␤-agonistinduced apoptosis. Methods and Results-To investigate whether overexpression of Hsp20 exerts protective effects in both ex vivo and in vivo ischemia/reperfusion (I/R) injury, we generated a transgenic (TG) mouse model with cardiac-specific overexpression of Hsp20 (10-fold). TG and wild-type (WT) hearts were then subjected to global no-flow I/R (45 minutes/120 minutes) using the Langendorff preparation. TG hearts exhibited improved recovery of contractile performance over the whole reperfusion period. This improvement was accompanied by a 2-fold decrease in lactate dehydrogenase released from the TG hearts. The extent of infarction and apoptotic cell death was also significantly decreased, which was associated with increased protein ratio of Bcl-2/Bax and reduced caspase-3 activity in TG hearts. Furthermore, in vivo experiments of 30-minute myocardial ischemia, via coronary artery occlusion, followed by 24-hour reperfusion, showed that the infarct region-to-risk region ratio was 8.1Ϯ1.1% in TG hearts (nϭ7), compared with 19.5Ϯ2.1% in WT hearts (nϭ11, PϽ0.001). Conclusions-Our data demonstrate that increased Hsp20 expression in the heart protects against I/R injury, resulting in improved recovery of cardiac function and reduced infarction. Thus, Hsp20 may constitute a new therapeutic target for ischemic heart diseases.

Background-Although remote ischemic stimuli have been shown to elicit cardioprotection against ischemia/reperfusion injury, there is little known about the effects of nonischemic stimuli. We previously described a remote cardioprotective effect of nonischemic surgical trauma (abdominal incision) called remote preconditioning of trauma (RPCT). In the present study, we elucidate mechanisms underlying this phenomenon. Methods and Results-We used a murine model of myocardial infarction to evaluate ischemia/reperfusion injury, and either abdominal surgical incision, or application of topical capsaicin, to elicit cardioprotection. We show that the cardioprotective effect of RPCT is initiated by skin nociception, and requires neurogenic signaling involving spinal nerves and activation of cardiac sensory and sympathetic nerves. Our results demonstrate bradykinin-dependent activation and repression, respectively, of PKC and PKC␦ in myocardium after RPCT, and we show involvement of the K ATP channels in cardioprotection. Finally, we show that topical application of capsaicin, which selectively activates C sensory fibers in the skin, mimics the cardioprotective effect of RPCT against myocardial infarction. Conclusions-Nontraumatic

Lumbar splanchnic (LSN) and sacral pelvic (PN) nerves convey different mechanosensory information from the colon to the spinal cord. Here we determined whether these pathways also differ in their chemosensitivity and receptor expression. Using an in vitro mouse colon preparation, individual primary afferents were tested with selective P2X and transient receptor potential vanilloid receptor 1 (TRPV1) receptor ligands. Afferent cell bodies in thoracolumbar and lumbosacral dorsal root ganglia (DRG) were retrogradely labelled from the colon and analysed for P2X 3 -and TRPV1-like immunoreactivity (LI). Forty per cent of LSN afferents responded to α,β-methylene adenosine 5 -triphosphate (α,β-meATP; 1 mM), an effect that was concentration dependent and reversed by the P2X antagonist pyridoxyl5-phosphate 6-azophenyl-2 ,4 -disulphonic acid (PPADS) (100 µM). Significantly fewer PN afferents (7%) responded to α,β-meATP. Correspondingly, 36% of colonic thoracolumbar DRG neurones exhibited P2X 3 -LI compared with only 19% of colonic lumbosacral neurones. Capsaicin (3 µM) excited 61% of LSN afferents and 47% of PN afferents; 82% of thoracolumbar and 50% of lumbosacral colonic DRG neurones displayed TRPV1-LI. Mechanically insensitive afferents were recruited by α,β-meATP or capsaicin, and were almost exclusive to the LSN. Capsaicin-responsive LSN afferents displayed marked mechanical desensitization after responding to capsaicin, which did not occur in capsaicin-responsive PN afferents. Therefore, colonic LSN and PN pathways differ in their chemosensitivity to known noxious stimuli and their corresponding receptor expression. As these pathways relay information that may relate to symptoms in functional gastrointestinal disease, these results may have implications for the efficacy of therapies targeting receptor modulation.

The ␣ -myosin heavy chain ( ␣ -MyHC) is the major contractile protein expressed in the myocardium of adult mice. We have produced mice carrying a null mutation of ␣ -MyHC by homologous recombination in murine ES cells. Homozygous null animals die between 11 and 12 d in utero of gross heart defects, while ␣ -MyHC ϩ / Ϫ heterozygotes survive and appear externally normal. The presence of a single functional ␣ -MyHC ϩ allele in heterozygous animals results in reduced levels of the transcript and protein as well as fibrosis and alterations in sarcomeric structure. Examination of heart function using a working heart preparation revealed severe impairment of both contractility and relaxation in a subset of the ␣ -MyHC ϩ / Ϫ animals. Thus, two ␣ -MyHC ϩ alleles are necessary for normal cardiac development, and hemizygosity for the normal allele can result in altered cardiac function. ( J. Clin. Invest. 1996Invest. . 98:1906Invest. -1917

Rationale: The levels of a small heat shock protein (Hsp)20 and its phosphorylation are increased on ischemic insults, and overexpression of Hsp20 protects the heart against ischemia/reperfusion injury. However, the mechanism underlying cardioprotection of Hsp20 and especially the role of its phosphorylation in regulating ischemia/reperfusion-induced autophagy, apoptosis, and necrosis remain to be clarified. Objective: Herein, we generated a cardiac-specific overexpression model, carrying nonphosphorylatable Hsp20, where serine 16 was substituted with alanine (Hsp20 S16A ). By subjecting this model to ischemia/reperfusion, we addressed whether: (1) the cardioprotective effects of Hsp20 are associated with serine 16 phosphorylation; (2) blockade of Hsp20 phosphorylation influences the balance between autophagy and cell death; and (3) the aggregation pattern of Hsp20 is altered by its phosphorylation. Methods and Results: Our results demonstrated that Hsp20 S16A hearts were more sensitive to ischemia/reperfusion injury, evidenced by lower recovery of contractile function and increased necrosis and apoptosis, compared with non-TG hearts. Interestingly, autophagy was activated in non-TG hearts but significantly inhibited in Hsp20 S16A hearts following ischemia/reperfusion. Accordingly, pretreatment of Hsp20 S16A hearts with rapamycin, an activator of autophagy, resulted in improvement of functional recovery, compared with saline-treated Hsp20 S16A hearts. Furthermore, on ischemia/reperfusion, the oligomerization pattern of Hsp20 appeared to shift to higher aggregates in Hsp20 S16A hearts. Conclusions: Collectively, these data indicate that blockade of Ser16-Hsp20 phosphorylation attenuates the cardioprotective effects of Hsp20 against ischemia/reperfusion injury, which may be attributable to suppressed autophagy and increased cell death. Therefore, phosphorylation of Hsp20 at serine 16 may represent a potential therapeutic target in ischemic heart disease. (Circ Res. 2009;105:1223-1231.)

Radiation injury of blood vessels was originally described more than a century ago and remains a contemporary clinical problem, despite dramatic advances in the field of radiation oncology (1). Clinical studies indicate that patients who have previously undergone radiation therapy for various malignancies—such as lymphoma, breast cancer, and head and neck cancer—are at increased risk for developing vascular disease (2). The consequences are significant; depending upon the study, the relative risk of suffering a clinical cardiovascular event (i.e., myocardial infarction, stroke) related to radiation therapy ranges from approximately 1.5- to 4.0-fold, and this risk is further amplified in the presence of traditional cardiovascular risk factors (3,4).