Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy.

Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5' AMP-activated protein kinase (AMPKα1/α2/ß2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment.

Blockade of the extracellular signal-regulated kinase pathway by U0126 attenuates neuronal damage following circulatory arrest.

OBJECTIVES: The extracellular signal-regulated kinase pathway of the mitogen-activated protein kinase signal transduction cascade has been implicated in the neuronal and endothelial dysfunction witnessed following cerebral ischemia-reperfusion injury. Extracellular signal-regulated kinase is activated by mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2. We evaluated the ability of a mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2-specific inhibitor (U0126) to block extracellular signal-regulated kinase activation and mitigate ischemic neuronal damage in a model of deep hypothermic circulatory arrest. METHODS: Piglets underwent normal flow cardiopulmonary bypass (control, n = 4), deep hypothermic circulatory arrest (n = 6), and deep hypothermic circulatory arrest with U0126 (n = 5) at 20 degrees C for 60 minutes. The deep hypothermic circulatory arrest with U0126 group was given 200 microg/kg of U0126 45 minutes prior to initiation of bypass followed by 100 microg/kg at reperfusion. Following 24 hours of post-cardiopulmonary bypass recovery, brains were harvested. Eleven distinct cortical regions were evaluated for neuronal damage using hematoxylin and eosin staining. A section of ischemic cortex was further evaluated by immunohistochemistry with rabbit polyclonal antibody against phosphorylated extracellular signal-regulated kinase 1/2. RESULTS: The deep hypothermic circulatory arrest and deep hypothermic circulatory arrest with U0126 groups displayed diffuse ischemic changes. However, the deep hypothermic circulatory arrest with U0126 group possessed significantly lower neuronal damage scores in the right frontal watershed zone of cerebral cortex, basal ganglia, and thalamus (P < or =.05) and an overall trend toward neuroprotection versus the deep hypothermic circulatory arrest group. This neuroprotection was accompanied by nearly complete blockade of phosphorylated extracellular signal-regulated kinase in the cerebral vascular endothelium. CONCLUSIONS: In this experimental model of deep hypothermic circulatory arrest, U0126 blocked extracellular signal-regulated kinase activation and provided a significant neuroprotective effect. These results support targeting of the extracellular signal-regulated kinase pathway for inhibition as a novel therapeutic approach to mitigate neuronal damage following deep hypothermic circulatory arrest.

Morbidity after procurement of radial arteries in diabetic patients and the elderly undergoing coronary revascularization.

BACKGROUND: The use of radial arteries for coronary revascularization is increasing. There remain concerns regarding alteration of upper extremity function after radial artery procurement. This study evaluates the functional morbidity in higher risk patients. METHODS: Between April 1997 and September 1999, 374 patients underwent unilateral or bilateral radial artery procurement. A questionnaire was used to evaluate symptoms related to motor and sensory function and changes in appearance after radial artery harvest. RESULTS: Two hundred eighty-nine patients were successfully interviewed. The average age was 63 years. Median follow-up was 9.5 months (range, 2 to 23 months). No patient suffered limb loss. Altered gross and fine motor function, residual pain, paresthesias, numbness, pallor, swelling, and altered temperature sensation were compared among diabetic patients, patients older than 70 years, and patients without these characteristics. CONCLUSIONS: Radial artery procurement for elective coronary revascularization can be done with minimal serious morbidity in higher risk patients. The most common symptoms were numbness and paresthesia. Despite the finding of greater residual pain in diabetic patients, we do not believe the use of radial artery conduits is contraindicated in these patients.

Late cardiac reoperation after cardiac transplantation.

BACKGROUND: The intermediate and long-term results of cardiac transplantation continue to improve. Subsequent cardiac procedures may be required to extend patient survival and protect graft function. METHODS: The medical records of all adult and pediatric cardiac transplant recipients who underwent a subsequent cardiac procedure at our institution were reviewed. RESULTS: Three hundred sixty patients have undergone primary orthotopic transplantation in our institution. Seventeen patients (12 adults, 5 children) underwent a subsequent procedure requiring cardiopulmonary bypass including cardiac retransplantation (10), coronary artery bypass grafting (3), ascending aortic replacement (2), tricuspid valve repair (1), and myotomy and myomectomy (1 patient). Mean interval from time of transplantation to second procedure was 8.3 years. There was one perioperative death. Two patients, both retransplants, died late postoperatively at 22 and 84 months, respectively. Overall mean follow-up in the late survivors is 26.6 months. All survivors are currently asymptomatic and doing well. CONCLUSIONS: A variety of subsequent cardiac procedures, in addition to retransplantation, can be performed safely in carefully selected cardiac transplant recipients. The intermediate term results are gratifying in terms of survival and freedom from symptoms.

Individual differences in field independence influence the ability to determine accurate needle angles.

OBJECTIVE: "Field dependence" is used in cognitive psychology to describe an individual's tendency to be visually distracted by the surrounding environment. Notwithstanding the role of field dependence in contexts in which spatial judgment is important, such as piloting an aircraft, to date, studies linking field dependence to surgical skills have been limited. We evaluated whether field dependence correlates with an ability to anticipate appropriate needle angles in a simulated setting. METHODS: Trainees underwent field dependence testing and then participated in a surgical skills exercise. Correlations between field dependence and surgical skill were computed. Specifically, cardiothoracic surgery residents (n=11) took a battery of cognitive examinations to assess general reasoning and visuospatial judgment. Two written tests, the Rod and Frame test and the Judgment of Line Orientation test, measured the degree of field dependence. The subjects then underwent surgical skills testing. Using a standard needle driver, the participants placed curved needles into a cylindrical silicone mitral valve model with 10 premarked needle entry and exit sites. The components assessed included the ability to load a needle on driver at the appropriate angle. RESULTS: The test results showed a parametric distribution, with internal cognitive testing controls demonstrating valid testing techniques and methods. Performance on the cognitive tests measuring spatial judgment and field dependence correlated significantly with skill at determining the appropriate needle angle load in an inverse fashion (Judgment of Line Orientation test, r=0.61, P<.05; Rod and Frame test, r=-0.52, P=.05), suggesting that residents who were not distracted by surrounding objects performed better. Performance on the cognitive examinations did not correlate with resident training level. CONCLUSIONS: Although our study was of a small cohort, the findings suggest that individuals described as field independent (not easily distracted by external visual cues) might possess improved ability to determine appropriate needle angle loads compared with field-dependent individuals. Additional studies examining the role field dependence might play in the acquisition and execution of surgical tasks are warranted.

Potential role of γδ T cell-derived IL-17 in acute cardiac allograft rejection.

BACKGROUND: Although αß T cells are known to participate in the development of acute cardiac allograft rejection, the role of γδ T cells remains poorly understood. We hypothesized that γδ T cells contribute to acute allograft rejection thru interleukin (IL)-17 production. METHODS: Donor hearts from FVB mice (H-2q) were heterotopically transplanted into C57BL/6-wild type (WT) and γδ T cell-deficient (TCRδ-/-) recipient mice (H-2b). Overall graft survival was monitored. Graft infiltrating cell profile, including γδ T cell subtype, cytokine expression, and myeloperoxidase activity were measured by flow cytometry, TaqMan (Applied Biosystems, Carlsbad, CA) polymerase chain reaction, and myeloperoxidase assay, respectively, on postoperative days 3 and 6. RESULTS: Graft survival was prolonged in TCRδ-/- recipients compared with WT controls. Graft infiltrating cells, including CD45+, CD4+, CD8+, and Gr1+ cells were significantly decreased in TCRδ-/- recipients compared with WT. Donor hearts transplanted into TCRδ-/- recipients had reduced IL-17 and IL-6 messenger RNA expression. Corroborating the gene expression, intracellular cytokine staining showed decreased IL-17 producing cells in TCRδ-/- recipients. Finally, Vγ1+ and Vγ4+ T cells did not produce IL-17, although both represent 20% to 30% total graft infiltrating γδ T cells. CONCLUSIONS: The γδ T cells promote acute cardiac allograft rejection, presumably by producing IL-17. The γδ T cell depletion may prove beneficial in prolonging allograft survival by suppressing IL-17 production.

Releasable annuloplasty ring insertion--a novel experimental implantation model.

OBJECTIVE: Experimental testing of annuloplasty ring (AR) effects requires a control group if the AR is implanted conventionally. Our goal was to develop a reversible AR insertion method that allows for beating heart assessment with and without an AR, providing the ability to evaluate the effects of an AR in the same animal (internal control). We tested the feasibility of this technique in an in vivo ovine model using four-dimensional (4-D) radiopaque marker tracking. METHODS: Before the operation, a rigid AR (Edwards Geoform, Edwards Lifesciences, Irvine, CA, USA) was prepared by stitching the middle parts of eight double-armed sutures evenly spaced through the ring fabric using a Spring Eye needle. The resulting loops were 'locked' with polypropylene sutures. In addition, two drawstring sutures were attached to the AR. Using cardiopulmonary bypass and cardioplegic arrest, 12 adult sheep had 16 radiopaque markers sewn to the mitral annulus. The AR was implanted by stitching the eight sutures equidistantly in a perpendicular direction through the mitral annulus. The sheep were transferred to the catheterisation laboratory and 4-D marker coordinates were obtained using biplane videofluoroscopy (60 Hz) with the AR inserted (Geo-AR). The locking sutures were then released, the AR was pulled up to the atrial roof using the drawstring sutures and another dataset was acquired (control). Maximum and minimum mitral annular areas (MAA(max), MAA(min)) during the cardiac cycle were derived from implanted markers. Data are provided from one representative animal. RESULTS: AR insertion and release were uneventful in all animals. Whereas the mitral annulus was dynamic in the control state (MAA(max): 9.0 cm(2), MAA(min): 7.8 cm(2)), mitral annular dynamics were abolished in the Geo-AR case (MAA(max): 6.2 cm(2), MAA(min): 6.0 cm(2)). CONCLUSIONS: This novel releasable AR implantation method is feasible and permits in vivo assessment of AR effects in the same heart. The new technique should facilitate experimental AR testing and promote the development of ARs based on physical criteria.

Retrospective analysis of local sensorimotor deficits after radial artery harvesting for coronary artery bypass grafting.

OBJECTIVES: The radial artery (RA) has gained widespread acceptance as a conduit for coronary artery bypass. We analyze patient-based data to determine risk factors for long-term upper limb morbidities associated with RA harvest for coronary artery bypass grafting. STUDY DESIGN/METHODS: Between April 1997 and March 2004, a total of 1030 patients underwent RA harvesting for coronary artery bypass grafting for a total of 1704 harvest sites. Patients were contacted by telephone and asked to report any ongoing severe sensory and functional motor deficits for each harvest site since surgery. Retrospective chart review was performed and preoperative risk factors were evaluated. Patient-based risk factors were evaluated for development of significant long-term local sensorimotor deficits including gender, elderly age (>70 y), diabetes, smoking, and whether the RA was harvested from the dominant hand. RESULTS: Successful evaluation of 629 patients for a total of 1048 RA harvest sites was completed. The mean follow-up time was 48.3 mo (range, 2 to 86 mo). The mean age of the patients analyzed was 62.2 y. On statistical analysis, diabetics and elderly did not report significantly greater functional or sensory deficits than nondiabetics and nonelderly, respectively. There was a significantly higher incidence of sensory deficits in smokers compared with nonsmoker patients (4.2% versus 1.4%; P = 0.005) but no difference in their functional impairment was noted. Harvesting from the dominant hand did not influence the occurrence of sensory or motor functional deficits. CONCLUSIONS: RA harvesting for coronary artery bypass grafting can be done with minimal serious long-term upper limb morbidity in higher risk patients. Based on our findings, harvesting of the RA from the dominant hand is not contraindicated in these patients.

Expression of multiple KCNE genes in human heart may enable variable modulation of I(Ks).

Voltage-gated potassium (K(V)) channels are modulated by at least three distinct classes of proteins including the KCNE family of single transmembrane accessory subunits. In the human genome, KCNE proteins are encoded by five genes designated KCNE1 through KCNE5. KCNE1 associates with KCNQ1 in vitro to generate a potassium current closely resembling the slowly activating delayed rectifier (I(Ks)). Other KCNE proteins also affect the activity of heterologously expressed KCNQ1. To investigate the potential physiological relevance of this gene family in human heart, we examined the relative expression of KCNQ1 and all five KCNE genes in samples derived from normal tissues representing major regions of human heart by real-time, quantitative RT-PCR. KCNE genes are expressed in human heart with a relative abundance ranking of KCNE1 > KCNE4 > KCNE5 approximately KCNE3 >> KCNE2. In situ hybridization revealed prominent expression of KCNE1 and KCNE3-5 in human atrial myocytes. In cardiomyopathic hearts, expression of KCNE1, KCNE3, KCNE4, and KCNQ1 was significantly increased, while KCNE2 and KCNE5 exhibited reduced expression. In a cell line stably expressing KCNQ1 and KCNE1, transient expression of KCNE3, KCNE4, or KCNE5 significantly altered I(Ks) current profiles. Even in the presence of additional KCNE1, KCNE4 and KCNE5 exert dominant effects on I(Ks). Although KCNE1 is the predominant KCNE family member expressed in human heart, the abundance of other KCNE transcripts including potential KCNQ1 suppressors (KCNE4 and KCNE5) and their altered expression patterns in disease lead us to speculate that a balance of KCNE accessory subunits may be important for cardiac K(V) channel function.