Regression of pressure-induced left ventricular hypertrophy is characterized by a distinct gene expression profile.

OBJECTIVE: Left ventricular hypertrophy is a highly prevalent and robust predictor of cardiovascular morbidity and mortality. Existing studies have finely detailed mechanisms involved with its development, yet clinical translation of these findings remains unsatisfactory. We propose an alternative strategy focusing on mechanisms of left ventricular hypertrophy regression rather than its progression and hypothesize that left ventricular hypertrophy regression is associated with a distinct genomic profile. METHODS: Minimally invasive transverse arch banding and debanding (or their respective sham procedures) were performed in C57Bl6 male mice. Left ventricular hypertrophy was assessed physiologically by means of transthoracic echocardiographic analysis, structurally by means of histology, and molecularly by means of real-time polymerase chain reaction. Mouse hearts were genomically analyzed with Agilent (Santa Clara, Calif) mouse 44k developmental gene chips. RESULTS: Compared with control animals, animals banded for 28 days had a robust hypertrophic response, as determined by means of heart weight/body weight ratio, histologic analysis, echocardiographic analysis, and fetal gene expression. These parameters were reversed within 1 week of debanding. Whole-genome arrays on left ventricular tissue revealed 288 genes differentially expressed during progression, 265 genes differentially expressed with regression, and only 23 genes shared by both processes. Signaling-related expression patterns were more prevalent with regression rather than the structure-related patterns associated with left ventricular hypertrophy progression. In addition, regressed hearts showed comparatively more changes in energy metabolism and protein production. CONCLUSIONS: This study demonstrates an effective model for characterizing left ventricular hypertrophy and reveals that regression is genomically distinct from its development. Further examination of these expression profiles will broaden our understanding of left ventricular hypertrophy and provide a novel therapeutic paradigm focused on promoting regression of left ventricular hypertrophy and not just halting its progression.

Inhibitory kappa B kinase-beta is a target for specific nuclear factor kappa B-mediated delayed cardioprotection.

OBJECTIVE: Myocardial ischemia/reperfusion injury remains a vexing problem. Translating experimental strategies that deliver protective agents before the ischemic insult limits clinical applicability. We targeted 2 proteins in the nuclear factor-kappaB pathway, inhibitory kappa B kinase-beta, and 26S cardiac proteasome to determine their cardioprotective effects when delivered during reperfusion. METHODS: C57BL/6 mice underwent left anterior descending artery occlusion for 30 minutes. An inhibitory kappa B kinase-beta inhibitor (Compound A), a proteasome inhibitor (PS-519), or vehicle was administered at left anterior descending artery release or 2 hours afterward. Infarct size was analyzed 24 hours later. Pressure-volume loops were performed at 72 hours. Serum and left ventricular tissue were collected 1 hour after injury to examine protein expression by enzyme-linked immunosorbent assay and Western blot. RESULTS: Inhibitory kappa B kinase-beta and proteasome inhibition significantly attenuated infarct size and preserved ejection fraction compared with the vehicle groups. When delivered even 2 hours after reperfusion, Compound A, but not PS-519, still decreased infarct size in mice. Finally, when delivered at reperfusion, successful inhibition of phosphorylated-p65 and decreased interleukin-6 and tumor necrosis factor-alpha levels occurred in mice given the inhibitory kappa B kinase-beta inhibitor, but not in mice with proteasome inhibition. CONCLUSION: Although inhibitory kappa B kinase-beta and proteasome inhibition at reperfusion attenuated infarct size after acute ischemia/reperfusion, only inhibitory kappa B kinase-beta inhibition provided cardioprotection through specific suppression of nuclear factor-kappaB signaling. This feature of highly targeted nuclear factor-kappaB inhibition might account for its delayed protective effects, providing a clinically relevant option for treating myocardial ischemia/reperfusion associated with unknown periods of ischemia and reperfusion as seen in cardiac surgery and acute coronary syndromes.

Proteasome inhibition promotes regression of left ventricular hypertrophy.

Current research in left ventricular hypertrophy (LVH) has largely focused on its progression and therapeutic mechanisms to prevent or slow its development. Few studies have centered on the regression or treatment of existing LVH. Nuclear factor-kappaB (NF-kappaB) is an inflammatory transcription factor that has been shown to be involved in LVH development. We hypothesized that proteasome-mediated NF-kappaB inhibition would prevent the development of LVH and promote its regression. A murine model of reversible hypertrophy was employed by administering isoproterenol (Iso) subcutaneously for 7-14 days. The proteasome inhibitor, PS-519, was delivered both concurrently and after Iso treatment. LVH was quantified by heart weight-to-body weight ratios, histology, transthoracic echocardiography, and hypertrophic gene expression. After 7 days of Iso treatment, all measures indicated successful development of LVH. Another group was treated for 7 days and then observed for an additional 7 days. This group experienced normalization of Iso-induced cell size, wall thickness, and beta-myosin heavy chain expression. When administered concurrently, PS-519 prevented Iso-induced LVH at 7 days. Furthermore, when PS-519 was given to animals during the second week of continued Iso treatment, these animals also experienced regression of hypertrophy by several measures. The success of proteasome inhibition in preventing LVH development and in promoting LVH regression, even in the face of continued hypertrophic stimulation, demonstrates its potential use as a clinically accessible strategy for treating patients with a variety of LVH-associated cardiomyopathies.

IKKbeta inhibition attenuates myocardial injury and dysfunction following acute ischemia-reperfusion injury.

Despite years of experimental and clinical research, myocardial ischemia-reperfusion (IR) remains an important cause of cardiac morbidity and mortality. The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated as a key mediator of reperfusion injury. Activation of NF-kappaB is dependent upon the phosphorylation of its inhibitor, IkappaBalpha, by the specific inhibitory kappaB kinase (IKK) subunit, IKKbeta. We hypothesized that specific antagonism of the NF-kappaB inflammatory pathway through IKKbeta inhibition reduces acute myocardial damage following IR injury. C57BL/6 mice underwent left anterior descending (LAD) artery ligation and release in an experimental model of acute IR. Bay 65-1942, an ATP-competitive inhibitor that selectively targets IKKbeta kinase activity, was administered intraperitoneally either prior to ischemia, at reperfusion, or 2 h after reperfusion. Compared with untreated animals, mice treated with IKKbeta inhibition had significant reduction in left ventricular infarct size. Cardiac function was also preserved following pretreatment with IKKbeta inhibition. These findings were further associated with decreased expression of phosphorylated IkappaBalpha and phosphorylated p65 in myocardial tissue. In addition, IKKbeta inhibition decreased serum levels of TNF-alpha and IL-6, two prototypical downstream effectors of NF-kappaB activity. These results demonstrate that specific IKKbeta inhibition can provide both acute and delayed cardioprotection and offers a clinically accessible target for preventing cardiac injury following IR.

Proteasome inhibition attenuates infarct size and preserves cardiac function in a murine model of myocardial ischemia-reperfusion injury.

BACKGROUND: Despite improvements in protection, myocardial ischemia-reperfusion remains an important cause of cardiac dysfunction. Multiple strategies exist experimentally; few are clinically accessible. Nuclear factor kappa-B (NF-kappaB) is a transcription factor central to the inflammatory response and is implicated in reperfusion injury. Its activation relies on the degradation of its inhibitory molecule, IkappaB, by the 20S proteasome. We hypothesized that proteasome inhibition would decrease the extent of infarction after temporary coronary occlusion. METHODS: C57Bl6 mice received a specific proteasome inhibitor (PS-519) and were subjected to 30 minutes of transient occlusion of the left anterior descending artery. After 24 hours of reperfusion, echocardiography was performed to evaluate ventricular function and hearts were excised and analyzed for infarct size, areas at risk, and molecular markers of injury and NF-kappaB activation. RESULTS: Compared with controls, PS-519 delivered before left anterior descending (coronary artery) ligation reduced the area of infarct without a change in the area at risk. Similar results were seen with PS-519 delivered at reperfusion. Echocardiography demonstrated a relative reduction in fractional shortening in the vehicle group of 9.8% versus only 2.7% in the PS-519 group. Markers of myocardial stress and injury were accordingly suppressed with PS-519. These physiologic findings were associated with PS-519 decreasing p65 and TNF expression while preserving IkappaB alpha expression. CONCLUSIONS: In this murine infarct model PS-519 significantly preserved regional myocardial function, reduced the size of infarction, and attenuated expression of myocardial inflammatory response genes. These data demonstrate that a currently available and well-tolerated inhibitor of NF-kappaB can decrease the risk of myocardial injury associated with ischemia-reperfusion.