AICAR-dependent AMPK activation improves scar formation in the aged heart in a murine model of reperfused myocardial infarction

We have demonstrated that scar formation after myocardial infarction (MI) is associated with an endogenous pool of CD44(pos)CD45(neg) multipotential mesenchymal stem cells (MSC). MSC differentiate into fibroblasts secreting collagen that forms a scar and mature into myofibroblasts that express alpha smooth muscle actin (α-SMA) that stabilizes the scar. In the aging mouse, cardiac repair after MI is associated with impaired differentiation of MSC; MSC derived from the aged hearts form dysfunctional fibroblasts that deposit less collagen in response to transforming growth factor beta-1 (TGF-β1) and poorly mature into myofibroblasts. We found in vitro that the defect in myofibroblast maturation can be remedied by AICAR, which activates non-canonical TGF-β signaling through AMP-activated protein kinase (AMPK). In the present study, we injected aged mice with AICAR and subjected them to 1h occlusion of the left anterior descending artery (LAD) and then reperfusion for up to 30days. AICAR-dependent AMPK signaling led to mobilization of an endogenous CD44(pos)CD45(neg) MSC and its differentiation towards fibroblasts and myofibroblasts in the infarct. This was accompanied by enhanced collagen deposition and collagen fiber maturation in the scar. The AICAR-treated group has demonstrated reduced adverse remodeling as indicated by improved apical end diastolic dimension but no changes in ejection fraction and cardiac output were observed. We concluded that these data indicate the novel, previously not described role of AMPK in the post-MI scar formation. These findings can potentially lead to a new therapeutic strategy for prevention of adverse remodeling in the aging heart.

Incidence of cholinesterase inhibitor therapy initiation among hospitalized patients

BACKGROUND

Initiation of cholinesterase inhibitor (ChEI) therapy for delirium during hospitalization is ineffective and may be associated with increased morbidity and mortality.

OBJECTIVE

To describe the incidence of initiating ChEI therapy during hospitalization.

DESIGN

A retrospective cross-sectional study.

SETTING

A tertiary-care academic medical center.

PATIENTS

Inpatient admissions from September 2010 through March 2011 with ChEI administration.

INTERVENTION

None.

MEASUREMENTS

Incidence of ChEI exposure, initiation of ChEI therapy, initiation of antipsychotics and benzodiazepines, infection, in-hospital mortality, and hospital length of stay.

RESULTS

The incidence of adult admissions with ChEI exposure and ChEI initiation was 23.2 (95% confidence interval: 21.2-25.4) and 2 (95% confidence interval 1.5-2.8) per 1000 admissions, respectively. Of 476 admissions receiving ChEI, 9% (n = 42) initiated therapy during the hospital stay and 91% (n = 434) continued on previously started therapy. Patients initiated on ChEI therapy frequently had infection (20 of 42) and were commonly initiated on antipsychotics (14 of 42) and benzodiazepines (13 of 42). Patients were hospitalized for a median of 2 days (interquartile range, 1-4) before initiation of ChEI and were exposed to therapy for a median of 3 days (interquartile range, 2-6). Of the 41 patients discharged from the hospital, 90% (n = 37) had orders to continue the ChEI postdischarge.

CONCLUSIONS

Despite a lack of evidence to support the practice, 9% of patients who received ChEI therapy were initiated during the inpatient setting. These patients were not routinely screened for delirium and frequently received treatments associated with delirium.

Initiation of cholinesterase inhibitors in an inpatient setting

We examined initiation of cholinesterase inhibitors (ChEIs) to determine whether ChEIs were being newly prescribed without sufficient evaluation for dementia and/or delirium and to explore whether there are differences in outcomes, such as mortality, hospital readmission rates, and duration of hospitalization, between patients newly started on ChEI and those who continued such medications prior to admission. Patients hospitalized in fiscal year 2008 and prescribed ChEI were identified. We reviewed electronic medical records. Of 282 patients, 15.6% (44) were new-starts and 84.4% (238) were continuations. Median length of stay was 16 days in new-starts versus 6 days in continuations (P < .05). Of new-starts, 38.6% were also treated of infection. Chart review additionally suggested possible treatment of delirium by initiation of benzodiazepines and antipsychotics in 11.4% and 22.7% of new-starts, respectively. We observed a substantive practice of initiating ChEIs in hospitalized elderly patients at risk of delirium. Although there was no difference in the 30-day mortality or readmission rates, new-starts were more likely to have a longer hospital stay than continuation patients.

Young little mice express a premature cardiovascular aging phenotype

To investigate the effect of growth hormone and insulin-like growth factor 1 deficiency on the aging mouse arterial system, we compared the hemodynamics in young (4 months) and old (30 months) growth hormone-releasing hormone receptor null dwarf (Little) mice and their wild-type littermates. Young Little mice had significantly lower peak and mean aortic velocity and significantly higher aortic impedance than young wild-type mice. However, unlike the wild-type mice, there were no significant changes in arterial function with age in the Little mice. Aortic pulse wave velocity estimated using characteristic impedance increased with age in the wild-type mice, but it changed minimally in the Little mouse. We therefore conclude that arterial function in Little mice expresses a premature aging phenotype at young age and may neither enhance nor reduce their longevity.

TNF receptor 1 signaling is critically involved in mediating angiotensin-II-induced cardiac fibrosis

Angiotensin-II (Ang-II) is associated with many conditions involving heart failure and pathologic hypertrophy. Ang-II induces the synthesis of monocyte chemoattractant protein-1 that mediates the uptake of CD34(+)CD45(+) monocytic cells into the heart. These precursor cells differentiate into collagen-producing fibroblasts and are responsible for the Ang-II-induced development of non-adaptive cardiac fibrosis. In this study, we demonstrate that in vitro, using a human monocyte-to-fibroblast differentiation model, Ang-II required the presence of tumor necrosis factor-alpha (TNF) to induce fibroblast maturation from monocytes. In vivo, mice deficient in both TNF receptors did not develop cardiac fibrosis in response to 1week Ang-II infusion. We then subjected mice deficient in either TNF receptor 1 (TNFR1-KO) or TNF receptor 2 (TNFR2-KO) to continuous Ang-II infusion. Compared to wild-type, in TNFR1-KO, but not in TNFR2-KO hearts, collagen deposition was greatly attenuated, and markedly fewer CD34(+)CD45(+) cells were present. Quantitative RT-PCR demonstrated a striking reduction of key fibrosis-related, as well as inflammation-related mRNA expression in Ang-II-treated TNFR1-KO hearts. TNFR1-KO animals also developed less cardiac remodeling, cardiac hypertrophy, and hypertension compared to wild-type and TNFR2-KO in response to Ang-II. Our data suggest that TNF induced Ang-II-dependent cardiac fibrosis by signaling through TNFR1, which enhances the generation of monocytic fibroblast precursors in the heart.

Aberrant differentiation of fibroblast progenitors contributes to fibrosis in the aged murine heart: role of elevated circulating insulin levels

With age, the collagen content of the heart increases, leading to interstitial fibrosis. We have shown that CD44(pos) fibroblasts derived from aged murine hearts display reduced responsiveness to TGF-β but, paradoxically, have increased collagen expression in vivo and in vitro. We postulated that this phenomenon was due to the defect in mesenchymal stem cell (MSC) differentiation in a setting of elevated circulating insulin levels and production that we observed in aging mice. We discovered that cultured fibroblasts derived from aged but not young cardiac MSCs of nonhematopoietic lineage displayed increased basal and insulin-induced (1 nM) collagen expression (2-fold), accompanied by increased farnesyltransferase (FTase) and Erk activities. In a quest for a possible mechanism, we found that a chronic pathophysiologic insulin concentration (1 nM) caused abnormal fibroblast differentiation of MSCs isolated from young hearts. Fibroblasts derived from these MSCs responded to insulin by elevating collagen expression as seen in untreated aged fibroblast cultures, suggesting a causal link between increased insulin levels and defective MSC responses. Here we report an insulin-dependent pathway that specifically targets collagen type I transcriptional activation leading to a unique mechanism of fibrosis that is TGF-β and inflammation-independent in the aged heart.

SRC-2 coactivator deficiency decreases functional reserve in response to pressure overload of mouse heart

A major component of the cardiac stress response is the simultaneous activation of several gene regulatory networks. Interestingly, the transcriptional regulator steroid receptor coactivator-2, SRC-2 is often decreased during cardiac failure in humans. We postulated that SRC-2 suppression plays a mechanistic role in the stress response and that SRC-2 activity is an important regulator of the adult heart gene expression profile. Genome-wide microarray analysis, confirmed with targeted gene expression analyses revealed that genetic ablation of SRC-2 activates the "fetal gene program" in adult mice as manifested by shifts in expression of a) metabolic and b) sarcomeric genes, as well as associated modulating transcription factors. While these gene expression changes were not accompanied by changes in left ventricular weight or cardiac function, imposition of transverse aortic constriction (TAC) predisposed SRC-2 knockout (KO) mice to stress-induced cardiac dysfunction. In addition, SRC-2 KO mice lacked the normal ventricular hypertrophic response as indicated through heart weight, left ventricular wall thickness, and blunted molecular signaling known to activate hypertrophy. Our results indicate that SRC-2 is involved in maintenance of the steady-state adult heart transcriptional profile, with its ablation inducing transcriptional changes that mimic a stressed heart. These results further suggest that SRC-2 deletion interferes with the timing and integration needed to respond efficiently to stress through disruption of metabolic and sarcomeric gene expression and hypertrophic signaling, the three key stress responsive pathways.

Abstract 229: TNF Receptor 1 Signaling Is Critically Involved in Mediating Angiotensin II-Induced Cardiac Fibrosis and Dysfunction

Angiotensin-II (Ang-II) plays a key role in the development of cardiomyopathies, as it is associated with many conditions involving heart failure and pathologic hypertrophy. Using a murine model of Ang-II infusion, we found that Ang-II induced the synthesis of monocyte chemoattractant protein 1 (MCP-1) that mediated the uptake of CD34 + /CD45 + monocytic cells into the heart. These precursor cells differentiated into collagen-producing fibroblasts and were responsible for the Ang-II-induced development of reactive fibrosis. Preliminary in vitro data using our monocyte-to-fibroblast differentiation model, suggested that Ang-II required the presence of TNF to induce fibroblast maturation from monocytes. In vivo, they indicated that in mice deficient of both TNF receptors (TNFR1 and TNFR2), Ang-II-induced fibrosis was absent. We now assessed the hypothesis that specific TNFR1 signaling is necessary for Ang-II-mediated cardiac fibrosis. Mice deficient in either TNFR1 (TNFR1-KO) or TNFR2 (TNFR2-KO) were subjected to continuous infusion of Ang-II for 1 to 6 weeks (n=6-8/group). Compared to wild-type, we found that in TNFR1-KO, but not in TNFR2-KO mouse hearts, collagen deposition was attenuated, as was cardiac α-smooth muscle actin protein (a marker for activated fibroblasts). When we isolated viable cardiac fibroblasts and characterized them by flow cytometry, we found that Ang-II infusion in TNFR1-KO, but not in TNFR2-KO, resulted in a marked decrease of CD34 + /CD45 + cells. Quantitative RT-PCR demonstrated a striking reduction of type 1 and 3 collagen, as well of MCP-1 mRNA expression in TNFR1-KO mouse hearts. Further measurements of cardiovascular parameters indicated that TNFR1-KO animals developed lesser Ang-II-mediated LV remodeling, smaller changes in E-linear deceleration times/rates over time, and displayed a lower Tei index (a heart rate independent marker of cardiac function), indicating less stiffness in TNFR1-KO hearts compared to wild-type and TNFR2-KO hearts. The data suggest that Ang-II-dependent cardiac fibrosis requires TNF and its signaling through TNFR1 which enhances the induction of MCP-1 and uptake of monocytic fibroblast precursors that are associated with reactive fibrosis and cardiac remodeling and function.

Abstract 208: Farnesylation-Dependent Fibrosis in the Aged Murine Heart

Mesenchymal stem cells (MSC) derived from the aged murine heart express reduced levels of the multipotency marker Nanog. These CD44 + CD45 - MSC inappropriately differentiate into fibroblasts characterized by markedly enhanced basal collagen expression. While collagen synthesis in cardiac fibroblasts derived from young mice is driven by TGF-β1, paradoxically, fibroblasts derived from the aged heart displayed reduced TGF-β1 responsiveness and decreased TGF-β receptor expression (ALK5). To resolve this apparent contradiction we looked for other pathways leading to collagen expression. We found that circulating insulin levels in aged mice were elevated ∼2.5 fold when compared to young animals. We hypothesized that increased circulating insulin levels drive MSC differentiation and caused upregulation of procollagen expression in cardiac fibroblasts. Our in vitro experiment confirmed that insulin at a pathophysiological concentration (1 nM) increased procollagen type I expression only in fibroblasts isolated from old hearts. As insulin can signal through substrate prenylation, cardiac fibroblasts isolated from aged mice had ∼2 fold greater basal activity of farnesyltransferase (FTase, enzyme that transfers the prenyl chain) than fibroblasts isolated from young mice. FTase activity was further increased when fibroblasts isolated from aged hearts were stimulated with insulin. Cells derived from 3 month old mice did not upregulate FTase activity in response to insulin. Basal expression of FTase regulatory subunit (FNTA) was also upregulated by 3 fold in aged fibroblasts and expression of catalytic subunit (FTNB) was increased with insulin stimulation. FTase inhibitor reduced procollagen synthesis in aged fibroblasts.

Here we present new data linking insulin-dependent upregulation of collagen type I synthesis via increased farnesylation in the aging heart.

Targeted deletion of microRNA-22 promotes stress-induced cardiac dilation and contractile dysfunction

BACKGROUND

Delineating the role of microRNAs (miRNAs) in the posttranscriptional gene regulation offers new insights into how the heart adapts to pathological stress. We developed a knockout of miR-22 in mice and investigated its function in the heart.

METHODS AND RESULTS

Here, we show that miR-22-deficient mice are impaired in inotropic and lusitropic response to acute stress by dobutamine. Furthermore, the absence of miR-22 sensitized mice to cardiac decompensation and left ventricular dilation after long-term stimulation by pressure overload. Calcium transient analysis revealed reduced sarcoplasmic reticulum Ca(2+) load in association with repressed sarcoplasmic reticulum Ca(2+) ATPase activity in mutant myocytes. Genetic ablation of miR-22 also led to a decrease in cardiac expression levels for Serca2a and muscle-restricted genes encoding proteins in the vicinity of the cardiac Z disk/titin cytoskeleton. These phenotypes were attributed in part to inappropriate repression of serum response factor activity in stressed hearts. Global analysis revealed increased expression of the transcriptional/translational repressor purine-rich element binding protein B, a highly conserved miR-22 target implicated in the negative control of muscle expression.

CONCLUSION

These data indicate that miR-22 functions as an integrator of Ca(2+) homeostasis and myofibrillar protein content during stress in the heart and shed light on the mechanisms that enhance propensity toward heart failure.

An educational program to assist clinicians in identifying elder investment fraud and financial exploitation

Due to age-related factors and illnesses, older adults may become vulnerable to elder investment fraud and financial exploitation (EIFFE). The authors describe the development and preliminary evaluation of an educational program to raise awareness and assist clinicians in identifying older adults at risk. Participants (n = 127) gave high ratings for the program, which includes a presentation, clinician pocket guide, and patient education brochure. Thirty-five respondents returned a completed questionnaire at the 6-month follow-up, with 69% (n = 24) of those indicating use of the program materials in practice and also reporting having identified 25 patients they felt were vulnerable to EIFFE. These findings demonstrate the value of providing education and practical tools to enhance clinic-based screening of this underappreciated but prevalent problem.

Abstract P245: Loss of Steroid Receptor Coactivator-2 in the Heart Results in a Return to the Fetal Gene Program

Steroid Receptor Coactivator-2 (SRC-2) is an integral transcriptional mediator of metabolism throughout the body with roles in both fatty acid and carbohydrate metabolism. Based on the critical link between cardiac function and cardiac metabolism, which itself has dynamic interplay between both fatty acid and carbohydrate use, we sought to determine if SRC-2 plays a role in controlling cardiac metabolism. Hearts from SRC-2-/- mice were analyzed by extensive gene expression profiling of major metabolic enzymes in fuel usage pathways as well as metabolomic analysis of major metabolites. Our results indicate that under normal conditions, loss of SRC-2 compromises the ability of the adult heart to metabolize fatty acid as its sole fuel source. We observe a gene expression profile that mimics the fetal heart and a metabolomic profile that suggests a reliance on anaerobic conversion of glucose to lactate for energy. This fetal gene switch is paralleled with changes of sarcomeric gene expression, along with several genes altered in response to stress. Interestingly, this long-term adaptive response is adequate to maintain cardiac function under normal conditions. However, SRC-2-/- mice do show impaired cardiac function as compared to SRC-2+/+ mice under hemodynamic stress from aortic banding. Surprisingly, this is accompanied by the absence of hypertrophy, which may be explained by decreased expression of serum response factor (SRF) and several of the transcription factors with which SRF is known to act. Taken together, loss of SRC-2 results in a cardiac phenotype characterized by a return to the fetal gene program that mimics the state of a stressed and/or aging heart. Further investigation of this mouse model may play an important role in understanding the mechanisms underlying the transcriptional events surrounding cardiac metabolic remodeling.

Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation

BACKGROUND

Aging is associated with oxidative stress, but underlying mechanisms remain poorly understood.

OBJECTIVE

We tested whether glutathione deficiency occurs because of diminished synthesis and contributes to oxidative stress in aging and whether stimulating glutathione synthesis with its precursors cysteine and glycine could alleviate oxidative stress.

DESIGN

Eight elderly and 8 younger subjects received stable-isotope infusions of [2H(2)]glycine, after which red blood cell (RBC) glutathione synthesis and concentrations, plasma oxidative stress, and markers of oxidant damage (eg, F(2)-isoprostanes) were measured. Elderly subjects were restudied after 2 wk of glutathione precursor supplementation.

RESULTS

Compared with younger control subjects, elderly subjects had markedly lower RBC concentrations of glycine (486.7 ± 28.3 compared with 218.0 ± 23.7 μmol/L; P < 0.01), cysteine (26.2 ± 1.4 compared with 19.8 ± 1.3 μmol/L; P < 0.05), and glutathione (2.08 ± 0.12 compared with 1.12 ± 0.18 mmol/L RBCs; P < 0.05); lower glutathione fractional (83.14 ± 6.43% compared with 45.80 ± 5.69%/d; P < 0.01) and absolute (1.73 ± 0.16 compared with 0.55 ± 0.12 mmol/L RBCs per day; P < 0.01) synthesis rates; and higher plasma oxidative stress (304 ± 16 compared with 346 ± 20 Carratelli units; P < 0.05) and plasma F(2)-isoprostanes (97.7 ± 8.3 compared with 136.3 ± 11.3 pg/mL; P < 0.05). Precursor supplementation in elderly subjects led to a 94.6% higher glutathione concentration, a 78.8% higher fractional synthesis rate, a 230.9% higher absolute synthesis rate, and significantly lower plasma oxidative stress and F(2)-isoprostanes. No differences in these measures were observed between younger subjects and supplemented elderly subjects.

CONCLUSIONS

Glutathione deficiency in elderly humans occurs because of a marked reduction in synthesis. Dietary supplementation with the glutathione precursors cysteine and glycine fully restores glutathione synthesis and concentrations and lowers levels of oxidative stress and oxidant damages. These findings suggest a practical and effective approach to decreasing oxidative stress in aging.

Disruption of K(2P)6.1 produces vascular dysfunction and hypertension in mice

K(2P)6.1, a member of the 2-pore domain K channel family, is highly expressed in the vascular system; however, its function is unknown. We tested the following hypotheses. K(2P)6.1 regulates the following: (1) systemic blood pressure; (2) the contractile state of arteries; (3) vascular smooth muscle cell migration; (4) proliferation; and/or (5) volume regulation. Mice lacking K(2P)6.1 (KO) were generated by deleting exon 1 of Kcnk6. Mean arterial blood pressure in both anesthetized and awake KO mice was increased by 17±2 and 26±3 mm Hg, respectively (P<0.05). The resting membrane potential in freshly dispersed vascular smooth muscle cells was depolarized by 17±2 mV in the KO compared with wild-type littermates (P<0.05). The contractile responses to KCl (P<0.05) and BAY K 8644 (P<0.01), an activator of L-type calcium channels, were enhanced in isolated segments of aorta from KO mice. However, there was no difference in the current density of L-type calcium channels. Responses to U46619, an agent that activates rho kinase, showed an enhanced contraction in aorta from KO mice (P<0.001). The BAY K 8644-mediated increase in contraction was decreased to wild-type levels when treated with Y27632, a rho kinase inhibitor, (P<0.05). K(2P)6.1 does not appear to be involved with migration, proliferation, or volume regulation in cultured vascular smooth muscle cells. We conclude that K(2P)6.1 deficiency induces vascular dysfunction and hypertension through a mechanism that may involve smooth muscle cell depolarization and enhanced rho kinase activity.

Novel approaches to perioperative assessment and intervention may improve long-term outcomes after colorectal cancer resection in older adults

Colorectal cancer (CRC) is common among older adults and surgical resection with curative intent is the primary treatment of CRC. Despite the changing demographics of CRC patients and increasing prevalence of multiple comorbidities, surgery is increasingly performed in this complex aging population. Clinically important short-term outcomes have improved for this population, but little is known about long-term outcomes. We review the literature to evaluate trends in CRC surgery in the geriatric population and the outcomes of surgical treatment. We explore the specific gaps in understanding longitudinal patient-centered outcomes of CRC treatment. We then propose adaptations from the geriatrics literature to better predict both short and long-term outcomes after CRC surgery. Interventions, such as prehabilitation, coupled with comprehensive geriatric assessment may be important future strategies for identifying vulnerable older patients, ameliorating the modifiable causes of vulnerability, and improving patient-centered longitudinal outcomes. Further research is needed to determine relevant aspects of geriatric assessments, identify effective intervention strategies, and demonstrate their validity in improving outcomes for at-risk older adults.

CCR2 mediates the uptake of bone marrow-derived fibroblast precursors in angiotensin II-induced cardiac fibrosis

Angiotensin II plays an important role in the development of cardiac hypertrophy and fibrosis, but the underlying cellular and molecular mechanisms are not completely understood. Recent studies have shown that bone marrow-derived fibroblast precursors are involved in the pathogenesis of cardiac fibrosis. Since bone marrow-derived fibroblast precursors express chemokine receptor, CCR2, we tested the hypothesis that CCR2 mediates the recruitment of fibroblast precursors into the heart, causing angiotensin II-induced cardiac fibrosis. Wild-type and CCR2 knockout mice were infused with angiotensin II at 1,500 ng·kg(-1)·min(-1). Angiotensin II treatment resulted in elevated blood pressure and cardiac hypertrophy that were not significantly different between wild-type and CCR2 knockout mice. Angiotensin II treatment of wild-type mice caused prominent cardiac fibrosis and accumulation of bone marrow-derived fibroblast precursors expressing the hematopoietic markers, CD34 and CD45, and the mesenchymal marker, collagen I. However, angiotensin II-induced cardiac fibrosis and accumulation of bone marrow-derived fibroblast precursors in the heart were abrogated in CCR2 knockout mice. Furthermore, angiotensin II treatment of wild-type mice increased the levels of collagen I, fibronectin, and α-smooth muscle actin in the heart, whereas these changes were not observed in the heart of angiotensin II-treated CCR2 knockout mice. Functional studies revealed that the reduction of cardiac fibrosis led to an impairment of cardiac systolic function and left ventricular dilatation in angiotensin II-treated CCR2 knockout mice. Our data demonstrate that CCR2 plays a pivotal role in the pathogenesis of angiotensin II-induced cardiac fibrosis through regulation of bone marrow-derived fibroblast precursors.

Doppler velocity measurements from large and small arteries of mice

With the growth of genetic engineering, mice have become increasingly common as models of human diseases, and this has stimulated the development of techniques to assess the murine cardiovascular system. Our group has developed nonimaging and dedicated Doppler techniques for measuring blood velocity in the large and small peripheral arteries of anesthetized mice. We translated technology originally designed for human vessels for use in smaller mouse vessels at higher heart rates by using higher ultrasonic frequencies, smaller transducers, and higher-speed signal processing. With these methods one can measure cardiac filling and ejection velocities, velocity pulse arrival times for determining pulse wave velocity, peripheral blood velocity and vessel wall motion waveforms, jet velocities for the calculation of the pressure drop across stenoses, and left main coronary velocity for the estimation of coronary flow reserve. These noninvasive methods are convenient and easy to apply, but care must be taken in interpreting measurements due to Doppler sample volume size and angle of incidence. Doppler methods have been used to characterize and evaluate numerous cardiovascular phenotypes in mice and have been particularly useful in evaluating the cardiac and vascular remodeling that occur following transverse aortic constriction. Although duplex ultrasonic echo-Doppler instruments are being applied to mice, dedicated Doppler systems are more suitable for some applications. The magnitudes and waveforms of blood velocities from both cardiac and peripheral sites are similar in mice and humans, such that much of what is learned using Doppler technology in mice may be translated back to humans.

Coronary flow reserve in mice: effects of age, coronary disease, and vascular loading

Mice are now commonly used as models of human cardiovascular diseases and conditions, but it is challenging to measure blood flow velocity in small vessels such as coronary arteries. Accordingly, we have developed a method using a 2 mm diameter 20 MHz pulsed Doppler probe applied to the chest of an anesthetized mouse to measure left main coronary blood flow velocity noninvasively. We also found that coronary flow velocity could be increased from baseline (B) to hyperemic (H) levels by changing the concentration of isoflurane gas anesthesia from 1% to 2.5% in oxygen and that the H levels are similar to or higher than those induced by adenosine. We used the ratio H/B to estimate coronary flow reserve (CFR) in young, adult, and old mice and in mice with atherosclerosis, coronary occlusion, pressure overload, and angiotensin infusion. We found that H/B increases with age from 2.4 (young) to 3.6 (old) and is reduced by all forms of coronary and vascular disease to as low as 1.1 by pressure overload. We conclude that CFR can be measured noninvasively and serially in mice as their cardiovascular systems adapt and remodel to various imposed or natural conditions, and that left main coronary flow reserve may be a good index of global cardiac function.

Bedside-to-Bench conference: research agenda for idiopathic fatigue and aging

The American Geriatrics Society, with support from the National Institute on Aging and the John A. Hartford Foundation, held its fifth Bedside-to-Bench research conference, "Idiopathic Fatigue and Aging," to provide participants with opportunities to learn about cutting-edge research developments, draft recommendations for future research, and network with colleagues and leaders in the field. Fatigue is a symptom that older persons, especially by those with chronic diseases, frequently experience. Definitions and prevalence of fatigue may vary across studies, across diseases, and even between investigators and patients. The focus of this review is on physical fatigue, recognizing that there are other related domains of fatigue (such as cognitive fatigue). Many definitions of fatigue involve a sensation of "low" energy, suggesting that fatigue could be a disorder of energy balance. Poor energy utilization efficiency has not been considered in previous studies but is likely to be one of the most important determinants of fatigue in older individuals. Relationships between activity level, capacity for activity, a tolerable rate of activity, and a tolerable fatigue threshold or ceiling underlie a notion of fatiguability. Mechanisms probably contributing to fatigue in older adults include decline in mitochondrial function, alterations in brain neurotransmitters, oxidative stress, and inflammation. The relationships between muscle function and fatigue are complex. A number of diseases (such as cancer) are known to cause fatigue and may serve as models for how underlying impaired physiological processes contribute to fatigue, particularly those in which energy utilization may be an important factor. A further understanding of fatigue will require two key strategies: to develop and refine fatigue definitions and measurement tools and to explore underlying mechanisms using animal and human models.

Feasibility of dual Doppler velocity measurements to estimate volume pulsations of an arterial segment

If volume flow was measured at each end of an arterial segment with no branches, any instantaneous differences would indicate that volume was increasing or decreasing transiently within the segment. This concept could provide an alternative method to assess the mechanical properties or distensibility of an artery noninvasively using ultrasound. The goal of this study was to determine the feasibility of using Doppler measurements of pulsatile velocity (opposed to flow) at two sites to estimate the volume pulsations of the intervening arterial segment. To test the concept over a wide range of dimensions, we made simultaneous measurements of velocity in a short 5 mm segment of a mouse common carotid artery and in a longer 20 cm segment of a human brachial-radial artery using a two-channel 20 MHz pulsed Doppler and calculated the waveforms and magnitudes of the volume pulsations during the cardiac cycle. We also estimated pulse wave velocity from the velocity upstroke arrival times and measured artery wall motion using tissue Doppler methods for comparison of magnitudes and waveforms. Volume pulsations estimated from Doppler velocity measurements were 16% for the mouse carotid artery and 4% for the human brachial artery. These values are consistent with the measured pulse wave velocities of 4.2 m/s and 10 m/s, respectively, and with the mouse carotid diameter pulsation. In addition, the segmental volume waveforms resemble diameter and pressure waveforms as expected. We conclude that with proper application and further validation, dual Doppler velocity measurements can be used to estimate the magnitude and waveform of volume pulsations of an arterial segment and to provide an alternative noninvasive index of arterial mechanical properties.

Monocytic fibroblast precursors mediate fibrosis in angiotensin-II-induced cardiac hypertrophy

Angiotensin-II (Ang-II) is an autacoid generated as part of the pathophysiology of cardiac hypertrophy and failure. In addition to its role in cardiac and smooth muscle contraction and salt retention, it was shown to play a major role in the cardiac interstitial inflammatory response and fibrosis accompanying cardiac failure. In this study, we examined a model of Ang-II infusion to clarify the early cellular mechanisms linking interstitial fibrosis with the onset of the tissue inflammatory response. Continuous infusion of Ang-II resulted in increased deposition of collagen in the heart. Ang-II infusion also resulted in the appearance of distinctive small, spindle-shaped, bone marrow-derived CD34(+)/CD45(+) fibroblasts that expressed collagen type I and the cardiac fibroblast marker DDR2 while structural fibroblasts were CD34(-)/CD45(-). Genetic deletion of monocyte chemoattractant protein (MCP)-1 (MCP-1-KO mice) prevented the Ang-II-induced cardiac fibrosis and the appearance of CD34(+)/CD45(+) fibroblasts. Real-time PCR in Ang-II-treated hearts revealed a striking induction of types I and III collagen, TGF-beta1, and TNF mRNA expression; this was obviated in Ang-II-infused MCP-1-KO hearts. In both wild-type and MCP-1-KO mice, Ang-II infusion resulted in cardiac hypertrophy, increased systolic function and hypertension which were not significantly different between the WT and MCP-1-KO mice over the 6-week course of infusion. In conclusion, the development of Ang-II-induced non-adaptive fibrosis in the heart required induction of MCP-1, which modulated the uptake and differentiation of a CD34(+)/CD45(+) fibroblast precursor population. In contrast to the inflammatory and fibrotic response, the hemodynamic response to Ang-II was not affected by MCP-1 in the first 6weeks.

Effect of isoflurane on aortic impedance in mice

Isoflurane is the most commonly used anesthetic in mice. We studied the effect of low and high levels of isoflurane (also a potent coronary vasodilator) on aortic impedance in mice. Aortic impedance was determined using pressure and flow velocity signals at baseline (B, pentobarbital anesthesia), low (Isol, 1%), and high (Iso2.5, 2.5%) levels of isoflurane. Significant differences were observed in peak and mean flow velocities, systolic, diastolic, mean and pulse pressures at B and Iso2.5. However in impedance indices only peripheral vascular resistance was significantly different. No changes were observed in the harmonic components that represent pulsatile characteristics of the aorta. Peak left ventricular (LV) pressure was significantly lower at Iso2.5 when compared to B, but +/-dP/dt and tau (time constant of LV relaxation) did not change significantly indicating that LV contractility was unaffected. These results show that various levels of isoflurane cause significant changes in vascular hemodynamics and care must be taken to minimize these differences when using isoflurane as an anesthesia.

Cerebrovascular responses in mice deficient in the potassium channel, TREK-1

We tested the hypothesis that TREK-1, a two-pore domain K channel, is involved with dilations in arteries. Because there are no selective activators or inhibitors of TREK-1, we generated a mouse line deficient in TREK-1. Endothelium-mediated dilations were not different in arteries from wild-type (WT) and TREK-1 knockout (KO) mice. This includes dilations of the middle cerebral artery to ATP, dilations of the basilar artery to ACh, and relaxations of the aorta to carbachol, a cholinergic agonist. The nitric oxide (NO) and endothelium-dependent hyperpolarizing factor components of ATP dilations were identical in the middle cerebral arteries of WT and TREK-1 KO mice. Furthermore, the NO and cyclooxygenase-dependent components were identical in the basilar arteries of the different genotypes. Dilations of the basilar artery to alpha-linolenic acid, an activator of TREK-1, were not affected by the absence of TREK-1. Whole cell currents recorded using patch-clamp techniques were similar in cerebrovascular smooth muscle cells (CVSMCs) from WT and TREK-1 KO mice. alpha-linolenic acid or arachidonic acid increased whole cell currents in CVSMCs from both WT and TREK-1 KO mice. The selective blockers of large-conductance Ca-activated K channels, penitrem A and iberiotoxin, blocked the increased currents elicited by either alpha-linolenic or arachidonic acid. In summary, dilations were similar in arteries from WT and TREK-1 KO mice. There was no sign of TREK-1-like currents in CVSMCs from WT mice, and there were no major differences in currents between the genotypes. We conclude that regulation of arterial diameter is not altered in mice lacking TREK-1.

Cardiomyocyte PDGFR-beta signaling is an essential component of the mouse cardiac response to load-induced stress

PDGFR is an important target for novel anticancer therapeutics because it is overexpressed in a wide variety of malignancies. Recently, however, several anticancer drugs that inhibit PDGFR signaling have been associated with clinical heart failure. Understanding this effect of PDGFR inhibitors has been difficult because the role of PDGFR signaling in the heart remains largely unexplored. As described herein, we have found that PDGFR-beta expression and activation increase dramatically in the hearts of mice exposed to load-induced cardiac stress. In mice in which Pdgfrb was knocked out in the heart in development or in adulthood, exposure to load-induced stress resulted in cardiac dysfunction and heart failure. Mechanistically, we showed that cardiomyocyte PDGFR-beta signaling plays a vital role in stress-induced cardiac angiogenesis. Specifically, we demonstrated that cardiomyocyte PDGFR-beta was an essential upstream regulator of the stress-induced paracrine angiogenic capacity (the angiogenic potential) of cardiomyocytes. These results demonstrate that cardiomyocyte PDGFR-beta is a regulator of the compensatory cardiac response to pressure overload-induced stress. Furthermore, our findings may provide insights into the mechanism of cardiotoxicity due to anticancer PDGFR inhibitors.

Multichannel pulsed Doppler signal processing for vascular measurements in mice

The small size, high heart rate and small tissue displacement of a mouse require small sensors that are capable of high spatial and temporal tissue displacement resolutions and multichannel data acquisition systems with high sampling rates for simultaneous measurement of high fidelity signals. We developed and evaluated an ultrasound-based mouse vascular research system (MVRS) that can be used to characterize vascular physiology in normal, transgenic, surgically altered and disease models of mice. The system consists of multiple 10/20MHz ultrasound transducers, analog electronics for Doppler displacement and velocity measurement, signal acquisition and processing electronics and personal computer based software for real-time and off-line analysis. In vitro testing of the system showed that it is capable of measuring tissue displacement as low as 0.1mum and tissue velocity (mum/s) starting from 0. The system can measure blood velocities up to 9m/s (with 10MHz Doppler at a PRF of 125kHz) and has a temporal resolution of 0.1 milliseconds. Ex vivo tracking of an excised mouse carotid artery wall using our Doppler technique and a video pixel tracking technique showed high correlation (R(2)=0.99). The system can be used to measure diameter changes, augmentation index, impedance spectra, pulse wave velocity, characteristic impedance, forward and backward waves, reflection coefficients, coronary flow reserve and cardiac motion in murine models. The system will facilitate the study of mouse vascular mechanics and arterial abnormalities resulting in significant impact on the evaluation and screening of vascular disease in mice.

In-vitro evaluation of sensors and amplifiers to measure left ventricular pressure in mice

Mice are becoming more common as research models, and several companies now manufacture sensors and instrumentation to measure left ventricular (LV) pressure and volume in mice. It is often assumed that pressure is easier to measure than volume, and that all sensors perform similarly, but there are differences. We measured in-vitro the frequency and step responses, immersion response, stability, accuracy, linearity, and sensitivity to lateral or bending force of several solid-state sensors and amplifiers commonly used in mice. We tested 4 microsensors each from Millar, Scisense, and RADI, and also fluid-filled catheters. All solid-state sensors were stable with drifts of 1 mmHg/hr, had flat frequency response to >1 kHz, and were accurate and linear to within +/- 2 mmHg from 0-300 mmHg. The frequency response of the fluid-filled catheter was down by 50% at 30 Hz. The amplifiers from Millar, Scisense, and RADI, had time delays of 0.2, 3.2 and 10.6 ms respectively. The Millar and RADI sensors were unresponsive to lateral forces, but the Scisense catheters had sensitivities as high as 5.3 mmHg/g. There are significant differences in solid state pressure sensors and amplifiers which could generate offsets, time delays, and distortions which could go unrecognized in-vivo.

Coronary flow reserve as an index of cardiac function in mice with cardiovascular abnormalities

Mice are now commonly used as models of human cardiovascular diseases and conditions, but it is challenging to measure blood flow velocity in small vessels such as coronary arteries. Accordingly, we have developed a method using a 2 mm diameter 20 MHz pulsed Doppler probe applied to the chest of anesthetized mice to measure left main coronary blood flow velocity noninvasively. We also found that coronary flow velocity could be increased from baseline (B) to hyperemic (H) levels by changing the concentration of isoflurane gas anesthesia from 1% to 2.5% in oxygen. We used the ratio B/H to estimate coronary flow reserve (CFR) in young, adult, and old mice and in mice with obesity, atherosclerosis, pressure overload hypertrophy, and coronary artery occlusion. We found that B/H increases with age from 2.4 (young) to 3.6 (old) and is decreased to as low as 1.1 by all forms of heart and vascular disease studied. We conclude that CFR can be measured noninvasively and serially in mice as their cardiovascular systems adapt and remodel to various imposed or natural conditions, and that coronary flow reserve may be a good index of overall cardiac function in mice and potentially in man.

Doppler estimation of reduced coronary flow reserve in mice with pressure overload cardiac hypertrophy

Aortic banding produces pressure overload cardiac hypertrophy in mice, leading to decompensated heart failure in four to eight weeks, but the effects on coronary blood flow velocity and reserve are unknown. To determine whether coronary flow reserve (CFR) was reduced, we used noninvasive 20-MHz Doppler ultrasound to measure left main coronary flow velocity at baseline (B) and at hyperemia (H) induced by low (1%) and high (2.5%) concentrations of isoflurane gas anesthesia. Ten mice were studied before (Pre) and at 1 d, 7 d, 14 d and 21 d after constricting the aortic arch to 0.4 mm diameter distal to the innominate artery. We also measured cardiac inflow and outflow velocities at the mitral and aortic valves and velocity at the jet distal to the aortic constriction. The pressure drop as estimated by 4V2 at the jet was 51 +/- 5.1 (mean +/- SE) mm Hg at 1 d, increasing progressively to 74 +/- 5.2 mm Hg at 21 d. Aortic and mitral blood velocities were not significantly different after banding (p = NS), but CFR, as estimated by H/B, dropped progressively from 3.2 +/- 0.3 before banding to 2.2 +/- 0.4, 1.7 +/- 0.3, 1.4 +/- 0.2 and 1.1 +/- 0.1 at 1 d, 7 d, 14 d and 21 d, respectively (all p < 0.01 vs. Pre). There was also a significant and progressive increase the systolic/diastolic velocity ratio (0.17 Pre to 0.92 at 21 d, all p < 0.01 vs. Pre) suggesting a redistribution of perfusion from subendocardium to subepicardium. We show for the first time that CFR, as estimated by the hyperemic response to isoflurane and measured by Doppler ultrasound, can be measured serially in mice and conclude that CFR is virtually eliminated in banded mice after 21 d of remodeling and hypertrophy. These results demonstrate that CFR is reduced in mice as in humans with cardiac disease but before the onset of decompensated heart failure.

Cardiac function in young and old Little mice

We studied cardiac function in young and old, wild-type (WT), and longer-living Little mice using cardiac flow velocities, echocardiographic measurements, and left ventricular (LV) pressure (P) to determine if enhanced reserves were in part responsible for longevity in these mice. Resting/baseline cardiac function, as measured by velocities, LV dimensions, +dP/dt(max), and -dP/dt(max), was significantly lower in young Little mice versus young WT mice. Fractional shortening (FS) increased significantly, and neither +dP/dt(max) nor -dP/dt(max) declined with age in Little mice. In contrast, old WT mice had no change in FS but had significantly lower +dP/dt(max) and -dP/dt(max) versus young WT mice. Significant decreases were observed in the velocity indices of old Little mice versus old WT mice, but other parameters were unchanged. The magnitude of dobutamine stress response remained unchanged with age in Little mice, while that in WT mice decreased. These data suggest that while resting cardiac function in Little mice versus WT mice is lower at young age, it is relatively unaltered with aging. Additionally, cardiac function in response to stress was maintained with age in Little mice but not in their WT counterparts. Thus, some mouse models of increased longevity may not be associated with enhanced reserves.

Aortic impedance in Little mice

The Little dwarf mouse lives 30% longer than its age-matched wild-type (WT) mouse. We determined aortic input impedance in 21 (8 Little, 13 WT) 4 month-old mice. Modulus of impedance was calculated from the Fourier transformed aortic pressure (P) and average luminal flow velocity (V(avg)) as |Z(i)| = |P|/|V(avg)|. Characteristic impedance was estimated by averaging the 2(nd)-10(th) harmonic of the impedance moduli. We found the impedance modulus |Z(i)| to be similar in the 2 groups (WT vs. Little; mean+/-SE) - peripheral resistance (10597+/-654 vs. 12932+/-1433 dyne-s/cm(3)), modulus at first harmonic (Z(1): 740+/-56 vs. 902+/-105 dyne-s/cm(3)), and characteristic impedance (Z(c): 441+/-34 vs. 470+/-60 dyne-s/cm(3)). Also, mean aortic velocity (20.1+/-1.1 vs. 16.5+/-1.8 cm/s) and mean aortic blood pressure (81.1+/-3.9 vs. 75.9+/-5.9 mmHg) were similar between the two groups. Impedance at low frequencies was slightly higher in the dwarf mice which may be due to the diminished systolic function as indicated by significant reduction in peak aortic velocity (84.0+/-3.2 vs. 70.1+/-1.2 cm/s, p<<0.01). Although modestly higher, the overall impedance in Little mice was similar to that in WT mice. This indicates that left ventricular (LV) afterload may not significantly be altered in Little mice.

TNF provokes cardiomyocyte apoptosis and cardiac remodeling through activation of multiple cell death pathways

Transgenic mice with cardiac-restricted overexpression of secretable TNF (MHCsTNF) develop progressive LV wall thinning and dilation accompanied by an increase in cardiomyocyte apoptosis and a progressive loss of cytoprotective Bcl-2. To test whether cardiac-restricted overexpression of Bcl-2 would prevent adverse cardiac remodeling, we crossed MHCsTNF mice with transgenic mice harboring cardiac-restricted overexpression of Bcl-2. Sustained TNF signaling resulted in activation of the intrinsic cell death pathway, leading to increased cytosolic levels of cytochrome c, Smac/Diablo and Omi/HtrA2, and activation of caspases -3 and -9. Cardiac-restricted overexpression of Bcl-2 blunted activation of the intrinsic pathway and prevented LV wall thinning; however, Bcl-2 only partially attenuated cardiomyocyte apoptosis. Subsequent studies showed that c-FLIP was degraded, that caspase-8 was activated, and that Bid was cleaved to t-Bid, suggesting that the extrinsic pathway was activated concurrently in MHCsTNF hearts. As expected, cardiac Bcl-2 overexpression had no effect on extrinsic signaling. Thus, our results suggest that sustained inflammation leads to activation of multiple cell death pathways that contribute to progressive cardiomyocyte apoptosis; hence the extent of such programmed myocyte cell death is a critical determinant of adverse cardiac remodeling.

Noninvasive ultrasonic measurement of arterial wall motion in mice

To facilitate assessment of arterial function, we developed a noninvasive Doppler method for measuring vessel motion in genetically altered mice. A 20 MHz probe was held by an alligator clip and positioned over the carotid arteries of 16 mice including six 3 to 5-month old wild-type (WT), four 30-month old senescent (Old), two apolipoprotein-E (ApoE), and four alpha smooth muscle actin (alphaSMA) mice. Doppler signals were obtained simultaneously from both vessel walls and from blood flow using one or two probes. The displacement signals from the near and far walls were subtracted to generate a diameter signal from which the excursion and an augmentation index were calculated. The excursion ranged between 13 microm (in ApoE) and 95 microm (in alphaSMA). The augmentation index was lowest in the WT mice (0.06) and highest in the Old mice (0.29). This noninvasive method is able to identify and confirm characteristic changes in arterial properties associated with age, atherosclerosis, and the absence of vascular tone.

Effects of isoflurane on coronary blood flow velocity in young, old and ApoE(-/-) mice measured by Doppler ultrasound

The commonly used anesthetic agent isoflurane (ISO) is a potent coronary vasodilator that could potentially be used in the assessment of coronary reserve, but its effects on coronary blood flow in mice are unknown. Coronary reserve is reduced by age, coronary artery disease and other cardiac pathologies in man, and some of these conditions can now be modeled in mice. Accordingly, we used Doppler ultrasound to measure coronary flow velocity in mice anesthetized with low (1%) and high (2.5%) levels of ISO to generate baseline (B) and elevated hyperemic (H) coronary flows, respectively. A 20-MHz Doppler probe was mounted in a micromanipulator and pointed trans-thoracically toward the origin of the left main coronary arteries of 10 6-wk (Young [Y]), 10 2-y (Old [O]) and 20 2-y apolipoprotein-E null (ApoE(-/-)) atherosclerotic (A) mice. In each mouse, we measured (B) and (H) peak diastolic velocities. B was 35.4 +/- 1.4 cm/s (Y), 24.8 +/- 1.6 (O) and 51.7 +/- 6.4 (A); H was 83.5 +/- 1.3 (Y), 86.5 +/- 1.9 (O) and 120 +/- 16.9 (A) and H/B was 2.4 +/- 0.1 (Y), 3.6 +/- 0.2 (O) and 2.5 +/- 0.2 (A). The differences in baseline velocities and H/B between O and Y and between A and O were significant (p < 0.01), whereas the differences in hyperemic velocities were not (p > 0.05). H/B was higher in old mice as a result of decreased baseline flow rather than increased hyperemic flow velocity. In contrast, ApoE(-/-) mice have increased baseline and hyperemic velocities, perhaps because of coronary lesions. The differences in baseline velocities between young and old mice could be the result of age-related changes in basal metabolism or to differential sensitivity to isoflurane. We conclude that Doppler ultrasound combined with coronary vasodilation via isoflurane could provide a convenient and noninvasive method to estimate coronary reserve in mice, but also that care must be taken when assessing coronary flow in mice under isoflurane anesthesia because of its potent coronary vasodilator properties.

Trigeminal trophic syndrome

Ulceration of the nose may be inadvertently induced by the patient. Although trigeminal trophic syndrome is an uncommon cause of chronic ulcers, healthcare providers should consider the possibility of this disorder when encountering a patient with nasal ulcerations. Trigeminal trophic syndrome most commonly occurs in older women following therapy for trigeminal neuralgia. The ulcers usually involve the nasal ala and paranasal areas. The clinical vignette of a man with a self-induced nasal ulcer secondary to trigeminal trophic syndrome, which was initially suspected to be skin cancer, is presented. Since nasal ulcerations can be secondary to other conditions, a lesional biopsy should be performed to exclude other diagnoses when trigeminal trophic syndrome is entertained. In addition to trigeminal trophic syndrome, the differential diagnosis of conditions that can cause nasal ulcers include factitial disorders with self-induced ulcerations (such as dermatitis artifacta and neurotic excoriations), granulomatous conditions, infectious diseases, malignancy, and pyoderma gangrenosum. Treatment of trigeminal trophic syndrome requires prevention of digital manipulation of the lesion-either by occluding contact with the ulcer, initiating psychotropic medication, or both. Psychiatric and/or pharmacologic intervention should be considered to reduce or resolve further habitual self-inflicted injury before surgical intervention.

Effect of cellular elements on pressure-velocity relationship in mice

The effect of cellular elements in the blood on peripheral vascular function in mice was evaluated using the pressure-velocity relationships in the iliac arteries of 5 wild type (WT) and 3 polycythemic (MH) mice. Pressure was obtained using a fluid filled catheter in the left iliac artery and blood velocity was measured in the right iliac artery using a 20 MHz pulsed Doppler probe. The proximal aorta was then occluded for one minute to allow flow velocity to decay to zero. The pressure-velocity relationship in the diastolic phase was determined before and after aortic occlusion. In both groups the pressure-velocity relationship was almost linear and the slopes were similar. However, the extrapolated zero-velocity intercept was significantly higher for the MH than WT mice before (55.4 +/- 4.0 vs. 36.2 +/- 4.1 mmHg, p<0.01) and after occlusion (50.7 +/- 5.5 vs. 23.8 +/- 3.1 mmHg, p<0.01). Hematocrits were 41%+/-3 in WT and 59%+/-3 in MH mice. These data show that cellular elements in the blood alter the pressure-velocity relationships in peripheral vessels of mice.

A pivotal role for endogenous TGF-beta-activated kinase-1 in the LKB1/AMP-activated protein kinase energy-sensor pathway

TGF-beta-activated kinase-1 (TAK1), also known as MAPKK kinase-7 (MAP3K7), is a candidate effector of multiple circuits in cardiac biology and disease. Here, we show that inhibition of TAK1 in mice by a cardiac-specific dominant-negative mutation evokes electrophysiological and biochemical properties reminiscent of human Wolff-Parkinson-White syndrome, arising from mutations in AMP-activated protein kinase (AMPK), most notably, accelerated atrioventricular conduction and impaired AMPK activation. To test conclusively the biochemical connection from TAK1 to AMPK suggested by this phenotype, we disrupted TAK1 in mouse embryos and embryonic fibroblasts by Cre-mediated recombination. In TAK1-null embryos, the activating phosphorylation of AMPK at T172 was blocked, accompanied by defective AMPK activity. However, loss of endogenous TAK1 causes midgestation lethality, with defective yolk sac and intraembryonic vasculature. To preclude confounding lethal defects, we acutely ablated floxed TAK1 in culture by viral delivery of Cre. In culture, endogenous TAK1 was activated by oligomycin, the antidiabetic drug metformin, 5-aminoimidazole-4-carboxamide riboside (AICAR), and ischemia, well established triggers of AMPK activity. Loss of TAK1 in culture blocked T172 phosphorylation induced by all three agents, interfered with AMPK activation, impaired phosphorylation of the endogenous AMPK substrate acetyl CoA carboxylase, and also interfered with activation of the AMPK kinase LKB1. Thus, by disrupting the endogenous TAK1 locus, we prove a pivotal role for TAK1 in the LKB1/AMPK signaling axis, an essential governor of cell metabolism.

Determinants of cardiac electrophysiological properties in mice

INTRODUCTION

The transgenic mouse is a popular model for human inherited cardiac disease. Electrophysiology (EP) studies have recently been performed in transgenic mice to characterize the electrical phenotype of the heart. However, little is known regarding the impact of experimental conditions or model selection on the outcome of EP studies in mice.

METHODS AND RESULTS

We investigated the effects of experimental conditions on mouse cardiac EP by (1) comparing the findings of transesophageal pacing with those of invasive intracardiac pacing, (2) elucidating the effects of commonly used anesthetic agents, and (3) determining the impact of changes in body temperature. We also investigated the effects of model selection by (1) studying the dependence on mouse strain, and (2) exploring the effects of age. We found that EP parameters derived by both transesophageal and intracardiac pacing/recordings methods were similar. On the other hand, the anesthetic mixture of ketamine, xylazine, and acepromazine had profound effects on cardiac EP compared to sodium pentobarbital or isoflurane. Meanwhile, compared to normal body temperature (97-99 F), low body temperature (92-94 F) prolonged most cardiac EP parameters, while high body temperature (102-104 F) had little effect. Heart rate was a sensitive indicator of changes in body temperature. Significant differences were observed in specialized conduction system properties among the mouse strains studied (FVB, C57, and DBA). Furthermore, atrial electrical remodeling was evidently associated with age, while ventricular electrical properties were virtually unaltered. In comparison with corresponding invasive EP parameters, we found that the QT interval was not a reliable EP index in the mouse.

CONCLUSIONS

Cardiac EP variability may result from differences in experimental techniques including anesthesia and body temperature and from differences in mouse selection including strain and age. The influence of these factors should be considered when characterizing the electrical phenotype of transgenic mice in cardiovascular research.

Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathy

Mutations in the cardiac ryanodine receptor 2 (RyR2) have been associated with catecholaminergic polymorphic ventricular tachycardia and a form of arrhythmogenic right ventricular dysplasia. To study the relationship between RyR2 function and these phenotypes, we developed knockin mice with the human disease-associated RyR2 mutation R176Q. Histologic analysis of hearts from RyR2(R176Q/+) mice revealed no evidence of fibrofatty infiltration or structural abnormalities characteristic of arrhythmogenic right ventricular dysplasia, but right ventricular end-diastolic volume was decreased in RyR2(R176Q/+) mice compared with controls, indicating subtle functional impairment due to the presence of a single mutant allele. Ventricular tachycardia (VT) was observed after caffeine and epinephrine injection in RyR2(R176Q/+), but not in WT, mice. Intracardiac electrophysiology studies with programmed stimulation also elicited VT in RyR2(R176Q/+) mice. Isoproterenol administration during programmed stimulation increased both the number and duration of VT episodes in RyR2(R176Q/+) mice, but not in controls. Isolated cardiomyocytes from RyR2(R176Q/+) mice exhibited a higher incidence of spontaneous Ca(2+) oscillations in the absence and presence of isoproterenol compared with controls. Our results suggest that the R176Q mutation in RyR2 predisposes the heart to catecholamine-induced oscillatory calcium-release events that trigger a calcium-dependent ventricular arrhythmia.

Targeted deletion of ROCK1 protects the heart against pressure overload by inhibiting reactive fibrosis

Ventricular myocyte hypertrophy is an important compensatory growth response to pressure overload. However, pathophysiological cardiac hypertrophy is accompanied by reactive fibrosis and remodeling. The Rho kinase family, consisting of ROCK1 and ROCK2, has been implicated in cardiac hypertrophy and ventricular remodeling. However, these previous studies relied heavily on pharmacological inhibitors,and not on gene deletion. Here we used ROCK1knockout (ROCK1-/-) mice to investigate role of ROCK1 in the development of ventricular remodeling induced by transverse aortic banding. We observed that ROCK1 deletion did not impair compensatory hypertrophic response induced by pressure overload. However, ROCK1-/- mice exhibited reduced perivascular and interstitial fibrosis, which was observed at 3 wk but not at 1 wk after the banding. The reduced fibrosis in the myocardium of ROCK1-/- mice was closely associated with reduced expression of a variety of extracellular matrix (ECM) proteins and fibrogenic cytokines such as TGFbeta2 and connective tissue growth factor. This inhibitory effect of ROCK1 deletion on pathophysiological induction of fibrogenic cytokines was further confirmed in the myocardium of transgenic mice with cardiomyocyte-specific overexpression of Gq. Thus, these results indicate that ROCK1 contributes to the development of cardiac fibrosis and induction of fibrogenic cytokines in cardiomyocytes in response to pathological stimuli.

Pulsed Doppler Signal Processing for Use in Mice: Applications

We have developed a high-frequency, high-resolution Doppler spectrum analyzer (DSPW) and compared its performance against an adapted clinical Medasonics spectrum analyzer (MSA) and a zero-crossing interval histogram (ZCIH) used previously by us to evaluate cardiovascular physiology in mice. The aortic velocity (means +/- SE: 92.7 +/- 2.5 versus 82.2 +/- 1.8 cm/s) and aortic acceleration (8194 +/- 319 versus 5178 +/- 191 cm/s2) determined by the DSPW were significantly higher compared to those by the MSA. Aortic ejection time was shorter (48.3 +/- 0.9 versus 64.6 +/- 1.8 ms) and the isovolumic relaxation was longer (17.6 +/- 0.6 versus 13.5 +/- 0.6 ms) when determined by the DSPW because it generates shorter temporal widths in the velocity spectra when compared to the MSA. These data indicate that the performance of the DSPW in evaluating cardiovascular physiology was better than that of the MSA. There were no significant differences between the aortic pulse wave velocity determined by using the ZCIH (391 +/- 16 cm/s) and the DSPW (394 +/- 20 cm/s). Besides monitoring cardiac function, we have used the DSPW for studying peripheral vascular physiology in normal, transgenic, and surgical models of mice. Several applications such as the detection of high stenotic jet velocities (> 4 m/s), vortex shedding frequencies (250 Hz), and subtle changes in wave shapes in peripheral vessels which could not obtained with clinical Doppler systems are now made possible with the DSPW.

Regulatable atrial natriuretic peptide gene therapy for hypertension

Hypertension (HTN) is a disease that begins with dysfunctional renal-sodium excretion and progresses to a syndrome of highly elevated systolic, diastolic, and mean arterial pressures. Inadequacies in the therapy of HTN have led to the investigation of the gene therapy of this disease by using systemic overproduction of vasodilatory peptides, such as atrial natriuretic peptide (ANP). However, gene-therapy approaches to HTN using ANP are limited by the need for long-term ANP gene expression and, most important, control of ANP gene expression. Here, we introduce a helper-dependent adenoviral vector carrying the mifepristone (Mfp)-inducible gene-regulatory system to control in vivo ANP expression. In the BPH/2 mouse model of HTN, Mfp-inducible ANP expression was seen for a period of >120 days after administration of vector. Physiological effects of ANP, including decreased systolic blood pressure, increased urinary cGMP output, and decreases in heart weight as a percentage of body weight were also under the control of Mfp. Given these capabilities, this vector represents a paradigm for the gene therapy of HTN.

Transgenic mouse model of ventricular preexcitation and atrioventricular reentrant tachycardia induced by an AMP-activated protein kinase loss-of-function mutation responsible for Wolff-Parkinson-White syndrome

BACKGROUND

We identified a gene (PRKAG2) that encodes the gamma-2 regulatory subunit of AMP-activated protein kinase (AMPK) with a mutation (Arg302Gln) responsible for familial Wolff-Parkinson-White (WPW) syndrome. The human phenotype consists of ventricular preexcitation, conduction abnormalities, and cardiac hypertrophy.

METHODS AND RESULTS

To elucidate the molecular basis for the phenotype, transgenic mice were generated by cardiac-restricted expression of the wild-type (TG(WT)) and mutant(TG(R302Q)) PRKAG2 gene with the cardiac-specific promoter alpha-myosin heavy chain. ECG recordings and intracardiac electrophysiology studies demonstrated the TG(R302Q) mice to have ventricular preexcitation (PR interval 10+/-2 versus 33+/-5 ms in TG(WT), P<0.05) and a prolonged QRS (20+/-5 versus 10+/-1 ms in TG(WT), P<0.05). A distinct AV accessory pathway was confirmed by electrical and pharmacological stimulation and substantiated by induction of orthodromic AV reentrant tachycardia. Enzymatic activity of AMPK in the mutant heart was significantly reduced (0.009+/-0.003 versus 0.025+/-0.001 nmol x min(-1) x g(-1) in nontransgenic mice), presumably owing to the mutation disrupting the AMP binding site. Excessive cardiac glycogen was observed. Hypertrophy was confirmed by increases in heart weight (296 versus 140 mg in TG(WT)) and ventricular wall thickness.

CONCLUSIONS

We have developed a genetic animal model of WPW that expresses a mutation responsible for a familial form of WPW syndrome with a phenotype identical to that of the human, including induction of supraventricular arrhythmia. The defect is due to loss of function of AMPK. Elucidation of the molecular basis should provide insight into development of the cardiac conduction system and accessory pathways.

Noninvasive ultrasonic measurement of arterial wall motion in mice

Despite the extensive use of genetically altered mice to study cardiovascular physiology and pathology, it remains difficult to quantify arterial function noninvasively in vivo. We have developed a noninvasive Doppler method for quantifying vessel wall motion in anesthetized mice. A 20-MHz probe was held by an alligator clip and positioned over the carotid arteries of 16 mice, including six 3- to 5-mo-old wild-type (WT), four 30-mo-old senescent (old), two apolipoprotein E null (ApoE), and four α-smooth muscle actin null (α-SMA) mice. Doppler signals were obtained simultaneously from both vessel walls and from blood flow. The calculated displacement signals from the near and far walls were subtracted to generate a diameter signal from which the excursion and an augmentation index were calculated. The excursion ranged between 13 μm (in ApoE) and 95 μm (in α-SMA). The augmentation index was lowest in the WT mice (0.06) and highest in the old mice (0.29). We conclude that Doppler signal processing may be used to measure vessel wall motion in mice with high spatial and temporal resolution and that diameter signals can replace pressure signals for calculating the augmentation index. This noninvasive method is able to identify and confirm characteristic changes in arterial properties previously associated with age, atherosclerosis, and the absence of vascular tone.

Activation of cardiac Cdk9 represses PGC-1 and confers a predisposition to heart failure

Hypertrophy allows the heart to adapt to workload but culminates in later pump failure; how it is achieved remains uncertain. Previously, we showed that hypertrophy is accompanied by activation of cyclin T/Cdk9, which phosphorylates the C-terminal domain of the large subunit of RNA polymerase II, stimulating transcription elongation and pre-mRNA processing; Cdk9 activity was required for hypertrophy in culture, whereas heart-specific activation of Cdk9 by cyclin T1 provoked hypertrophy in mice. Here, we report that alphaMHC-cyclin T1 mice appear normal at baseline yet suffer fulminant apoptotic cardiomyopathy when challenged by mechanical stress or signaling by the G-protein Gq. At pathophysiological levels, Cdk9 activity suppresses many genes for mitochondrial proteins including master regulators of mitochondrial function (peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), nuclear respiratory factor-1). In culture, cyclin T1/Cdk9 suppresses PGC-1, decreases mitochondrial membrane potential, and sensitizes cardiomyocytes to apoptosis, effects rescued by exogenous PGC-1. Cyclin T1/Cdk9 inhibits PGC-1 promoter activity and preinitiation complex assembly. Thus, chronic activation of Cdk9 causes not only cardiomyocyte enlargement but also defective mitochondrial function, via diminished PGC-1 transcription, and a resulting susceptibility to apoptotic cardiomyopathy.

Disruption of Rho signaling results in progressive atrioventricular conduction defects while ventricular function remains preserved

Recent studies suggest that RhoA and Rac1 mediate hypertrophic signals in cardiac myocyte hypertrophy. However, effects on cardiac function caused by inhibition of their activity in the heart have yet to be evaluated. Cardiac-specific inhibition of Rho family protein activities was achieved by expressing Rho GDIalpha, an endogenous specific GDP dissociation inhibitor for Rho family proteins, using the alpha-myosin heavy-chain promoter. Increased expression of Rho GDIalpha led to atrial arrhythmias and mild ventricular hypertrophy in adult mice (4-7 months). However, left ventricular systolic and diastolic function was largely preserved before and after the development of cardiac hypertrophy, indicating that Rho GTPases are not required to maintain ventricular contractile function under basal physiological condition. Electrocardiography and intracardiac electrophysiological studies revealed first-degree atrioventricular (AV) block in the transgenic heart at 1 week of age, which further progressed into second-degree AV block at 4 weeks of age before the development of cardiac hypertrophy. Expression of connexin 40 dramatically decreased from 1 week to 4 weeks of age in the transgenic heart, which may contribute in part to the conduction defects in the transgenic mice. This study provides novel evidence for an important role of Rho GTPases in regulating AV conduction.

Bcl-2 overexpression corrects mitochondrial defects and ameliorates inherited desmin null cardiomyopathy

One of the hallmarks of cardiomyopathy and heart failure is pronounced and progressive cardiomyocyte death. Understanding the mechanisms involved in cardiomyocyte cell death is a topic of great interest for treatment of cardiac disease. Mice null for desmin, the muscle-specific member of the intermediate filament gene family, develop cardiomyopathy characterized by extensive cardiomyocyte death, fibrosis, calcification, and eventual heart failure. The earliest ultrastructural defects are observed in mitochondria. In the present study, we have demonstrated that these mitochondrial abnormalities are the primary cause of the observed cardiomyopathy and that these defects can be ameliorated by overexpression of bcl-2 in desmin null heart. Overexpression of bcl-2 in the desmin null heart results in correction of mitochondrial defects, reduced occurrence of fibrotic lesions in the myocardium, prevention of cardiac hypertrophy, restoration of cardiomyocyte ultrastructure, and significant improvement of cardiac function. Furthermore, we have found that loss of desmin also diminishes the capacity of mitochondria to resist exposure to calcium, a defect that can be partially restored by bcl-2 overexpression. These results point to a unique function for desmin in protection of mitochondria from calcium exposure that can be partially rescued by overexpression of bcl-2. We show that bcl-2 cardiac overexpression has provided significant improvement of an inherited form of cardiomyopathy, revealing the potential for bcl-2, and perhaps other genes in the family, as therapeutic agents for heart disease of many types, including inherited forms.