G protein-coupled receptor (GPCR) kinases (GRKs) are critical regulators of cellular signaling and function. In cardiomyocytes, GRK2 and GRK5 are two GRKs important for myocardial regulation, and both have been shown to be up-regulated in the dysfunctional heart. We report that increased levels and activity of GRK5 in failing myocardium may have unique significance due to its nuclear localization, a property not shared by GRK2. We find that transgenic mice with elevated cardiac GRK5 levels have exaggerated hypertrophy and early heart failure compared with control mice after pressure overload. This pathology is not present in cardiac GRK2-overexpressing mice or in mice with overexpression of a mutant GRK5 that is excluded from the nucleus. Nuclear accumulation of GRK5 is enhanced in myocytes after aortic banding in vivo and in vitro in myocytes after increased Gαq activity, the trigger for pressure-overload hypertrophy. GRK5 enhances activation of MEF2 in concert with Gq signals, demonstrating that nuclear localized GRK5 regulates gene transcription via a pathway critically linked to myocardial hypertrophy. Mechanistically, we show that this is due to GRK5 acting, in a non-GPCR manner, as a class II histone deacetylase (HDAC) kinase because it can associate with and phosphorylate the myocyte enhancer factor-2 repressor, HDAC5. Moreover, significant HDAC activity can be found with GRK5 in the heart. Our data show that GRK5 is a nuclear HDAC kinase that plays a key role in maladaptive cardiac hypertrophy apparently independent of any action directly on GPCRs.

Abstract-Myocardial G protein-coupled receptor kinase (GRK)2 is a critical regulator of cardiac ␤-adrenergic receptor (␤AR) signaling and cardiac function. Its upregulation in heart failure may further depress cardiac function and contribute to mortality in this syndrome. Preventing GRK2 translocation to activated ␤AR with a GRK2-derived peptide that binds G ␤ ␥ (␤ARKct) has benefited some models of heart failure, but the precise mechanism is uncertain, because GRK2 is still present and ␤ARKct has other potential effects. We generated mice in which cardiac myocyte GRK2 expression was normal during embryonic development but was ablated after birth (␣MHC-CreϫGRK2 fl/fl) or only after administration of tamoxifen (␣MHC-MerCreMerϫGRK2 fl/fl) and examined the consequences of GRK2 ablation before and after surgical coronary artery ligation on cardiac adaptation after myocardial infarction. Absence of GRK2 before coronary artery ligation prevented maladaptive postinfarction remodeling and preserved ␤AR responsiveness. Strikingly, GRK2 ablation initiated 10 days after infarction increased survival, enhanced cardiac contractile performance, and halted ventricular remodeling. These results demonstrate a specific causal role for GRK2 in postinfarction cardiac remodeling and heart failure and support therapeutic approaches of targeting GRK2 or restoring ␤AR signaling by other means to improve outcomes in heart failure.

Background— Diminished cardiac S100A1 protein levels are characteristic of ischemic and dilated human cardiomyopathy. Because S100A1 has recently been identified as a Ca 2+ -dependent inotropic factor in the heart, this study sought to explore the pathophysiological relevance of S100A1 levels in development and progression of postischemic heart failure (HF). Methods and Results— S100A1-transgenic (STG) and S100A1-knockout (SKO) mice were subjected to myocardial infarction (MI) by surgical left anterior descending coronary artery ligation, and survival, cardiac function, and remodeling were compared with nontransgenic littermate control (NLC) and wild-type (WT) animals up to 4 weeks. Although MI size was similar in all groups, infarcted S100A1-deficient hearts (SKO-MI) responded with acute contractile decompensation and accelerated transition to HF, rapid onset of cardiac remodeling with augmented apoptosis, and excessive mortality. NLC/WT-MI mice, displaying a progressive decrease in cardiac S100A1 expression, showed a later onset of cardiac remodeling and progression to HF. Infarcted S100A1-overexpressing hearts (STG-MI), however, showed preserved global contractile performance, abrogated apoptosis, and prevention from cardiac hypertrophy and HF with superior survival compared with NLC/WT-MI and SKO-MI. Both Gq-protein–dependent signaling and protein kinase C activation resulted in decreased cardiac S100A1 mRNA and protein levels, whereas Gs-protein–related signaling exerted opposite effects on cardiac S100A1 abundance. Mechanistically, sarcoplasmic reticulum Ca 2+ cycling and β-adrenergic signaling were severely impaired in SKO-MI myocardium but preserved in STG-MI. Conclusions— Our novel proof-of-concept study provides evidence that downregulation of S100A1 protein critically contributes to contractile dysfunction of the diseased heart, which is potentially responsible for driving the progressive downhill clinical course of patients with HF.

Background-A salient characteristic of dysfunctional myocardium progressing to heart failure is an upregulation of the adenylyl cyclase inhibitory guanine nucleotide (G) protein ␣ subunit, G␣ i2 . It has not been determined conclusively whether increased Gi activity in the heart is beneficial or deleterious in vivo. Gi signaling has been implicated in the mechanism of cardioprotective agents; however, no in vivo evidence exists that any of the G␣ subunits are cardioprotective. We have created a novel molecular tool to specifically address the role of Gi proteins in normal and dysfunctional myocardium. Methods and Results-We have developed a class-specific Gi inhibitor peptide, GiCT, composed of the region of G␣ i2 that interacts specifically with G protein-coupled receptors. GiCT inhibits Gi signals specifically in vitro and in vivo, whereas Gs and Gq signals are not affected. In vivo expression of GiCT in transgenic mice effectively causes a "functional knockout" of cardiac G␣ i2 signaling. Inducible, cardiac-specific GiCT transgenic mice display a baseline phenotype consistent with nontransgenic mice. However, when subjected to ischemia/reperfusion injury, GiCT transgenic mice demonstrate a significant increase in infarct size compared with nontransgenic mice (from 36.9Ϯ2.5% to 50.9Ϯ4.3%). Mechanistically, this post-ischemia/reperfusion phenotype includes increased myocardial apoptosis and resultant decreased contractile performance. Conclusions-Overall, our results demonstrate the in vivo utility of GiCT to dissect specific mechanisms attributed to Gi signaling in stressed myocardium. Our results with GiCT indicate that upregulation of G␣ i2 is an adaptive protective response after ischemia to shield myocytes from apoptosis.

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Owing to its osteoinductive and osteoconductive properties and the presence of osteogenic cells, freshly harvested autologous bone graft is the gold standard for skeletal reconstruction where there is inadequate native bone. Whereas these characteristics are difficult to replicate, engineered, commercially available bone graft substitutes aim to achieve a comparable osseoregenerative profile. This work furnishes the reader with an understanding of the predominant classes of bone graft substitutes available for reconstruction of upper extremity CME INFORMATION AND DISCLOSURESThe Journal of Hand Surgery will contain at least 2 clinically relevant articles selected by the editor to be offered for CME in each issue. For CME credit, the participant must read the articles in print or online and correctly answer all related questions through an online examination. The questions on the test are designed to make the reader think and will occasionally require the reader to go back and scrutinize the article for details.The JHS CME Activity fee of $15.00 includes the exam questions/answers only and does not include access to the JHS articles referenced.Statement of Need: This CME activity was developed by the JHS editors as a convenient education tool to help increase or affirm reader's knowledge. The overall goal of the activity is for participants to evaluate the appropriateness of clinical data and apply it to their practice and the provision of patient care. Accreditation:The American Society for Surgery of the Hand (ASSH) is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.AMA PRA Credit Designation: The ASSH designates this Journal-Based CME activity for a maximum of 1.00 AMA PRA Category 1 Creditsä. Physicians should claim only the credit commensurate with the extent of their participation in the activity.ASSH Disclaimer: The material presented in this CME activity is made available by the ASSH for educational purposes only. This material is not intended to represent the only methods or the best procedures appropriate for the medical situation(s) discussed, but rather it is intended to present an approach, view, statement, or opinion of the authors that may be helpful, or of interest, to other practitioners. Examinees agree to participate in this medical education activity, sponsored by the ASSH, with full knowledge and awareness that they waive any claim they may have against the ASSH for reliance on any information presented. The approval of the US Food and Drug Administration (FDA) is required for procedures and drugs that are considered experimental. Instrumentation systems discussed or reviewed during this educational activity may not yet have received FDA approval.

When selectively overexpressed in mouse heart, TNF-alpha effects the development of a cardiomyopathy that closely mimics that seen in human failing hearts. It has been suggested that two intracellular signaling pathways, the Akt protein kinase and the NF-kappaB transcription factor, mediated TNF-alpha signaling. The present experiments assessed the effects of TNF-alpha overexpression on these two target proteins in vivo. We measured cardiac Akt kinase phosphorylation and NF-kappaB activity in mice overexpressing TNF-alpha (TNF1.6). Both basal and insulin-stimulated Akt phosphorylation were reduced by almost 70% by TNF-alpha overexpression. By contrast, NF-kappaB was robustly activated. These effects were absent when TNF-alpha receptor 1 (TNFR1) was selectively ablated. Cardiomyocyte-specific overexpression of the dominant-negative inhibitory kappaB protein transgene and subsequent inhibition of NF-kappaB activity attenuated the effects of TNF-alpha on Akt phosphorylation. NF-kappaB inhibition also significantly improved fractional shortening and diminished ventricular hypertrophy and survival without affecting infiltrative inflammation or cytokine expression. Thus, while overexpression of TNF-alpha effected a marked Akt inhibition and NF-kappaB activation in mouse hearts, inhibition of NF-kappaB offered salutary benefits mediated at least in part through activation of Akt.

Caveolin are scaffolding proteins that are integral components of caveolae, flask shaped invaginations in the membranes of all mammalian cells. Caveolins-1 and −3 are expressed ubiquitously whereas caveolin-3 is found only in muscle. The role of caveolin-3 in heart muscle disease is controversial. The present study was undertaken to assess the effects of left ventricular dysfunction on the expression of caveolin proteins using two well-characterized models of murine heart failure and failing human heart. Mice with constitutive overexpression of A 1 -adenosine receptor (A 1 -TG) demonstrate cardiac dilatation and decreased left ventricular function at 10 weeks of age. This was accompanied by a marked decrease in caveolin-3 mRNA and protein levels when compared to non-TG control mice. The change in caveolin-3 expression was selective as levels of caveolin-1 and −2 did not change. Confocal imaging of myocytes isolated from A 1 -AR TG mice demonstrated a loss of the plate like appearance of T-tubules. Caveolin-3 levels were also reduced in hearts from mice over-expressing TNFα. There was a direct relationship between caveolin-3 expression and fractional shortening in all mice that were studied (r= 0.65; p<0.001).Although we could not demonstrate a significant decrease in caveolin-3 levels in failing human heart, we did find a direct correlation (r=0.7; p<0.05) between levels of caveolin-3 protein and Ca 2+ -ATPase, a marker of the heart failure phenotype. These results suggest a relationship between left ventricular dysfunction and caveolin-3 levels and suggest that caveolin-3 may provide a novel target for heart failure therapy.