Cardiac human bitter taste receptors contain naturally occurring variants that alter function

Bitter taste receptors (T2R) are a subfamily of G protein-coupled receptors that enable humans to detect aversive and toxic substances. The ability to discern bitter compounds varies between individuals and is attributed mainly to naturally occurring T2R polymorphisms. T2Rs are also expressed in numerous non-gustatory tissues, including the heart, indicating potential contributions to cardiovascular physiology. In this study. T2Rs that have previously been identified in human cardiac tissues (T2Rs - 10, 14, 30, 31, 46 and 50) and their naturally occurring polymorphisms were functionally characterised. The ligand-dependent signaling responses of some T2R variants were completely abolished (T2R30 Leu252 and T2R46 Met228), whereas other receptor variants had moderate changes in their maximal response, but not potency, relative to wild type. Using a cAMP fluorescent biosensor, we reveal the productive coupling of T2R14, but not the T2R14 Phe201 variant, to endogenous Gαi. Modeling revealed that these variants resulted in altered interactions that generally affected ligand binding (T2R30 Leu252) or Gα protein interactions (T2R46 Met228 and T2R14 Phe201), rather than receptor structural stability. Interestingly, this study is the first to show a difference in signaling for T2R50 Tyr203 (rs1376251) which has been associated with cardiovascular disease. The observation of naturally occurring functional variation in the T2Rs with the greatest expression in the heart is important, as their discovery should prove useful in deciphering the role of T2Rs within the cardiovascular system.

Periconceptional alcohol alters in vivo heart function in ageing female rat offspring: Possible involvement of oestrogen receptor signalling

NEW FINDINGS

What is the central question of this study? What are the cardiovascular consequences of periconceptual ethanol on offspring throughout the lifespan? What is the main finding and its importance? It is shown for the first time that periconceptional alcohol has sex-specific effects on heart growth, with ageing female offspring exhibiting decreased cardiac output. Altered in vivo cardiac function in ageing female offspring may be linked to changes in cardiac oestrogen receptor expression.

ABSTRACT

Alcohol exposure throughout gestation is detrimental to cardiac development and function. Although many women decrease alcohol consumption once aware of a pregnancy, exposure prior to recognition is common. We, therefore, examined the effects of periconceptional alcohol exposure (PC:EtOH) on heart function, and explored mechanisms that may contribute. Female Sprague-Dawley rats received a liquid diet ±12.5% v/v ethanol from 4 days prior to mating until 4 days after mating (PC:EtOH). Cardiac function was assessed via echocardiography, and offspring were culled at multiple time points for assessment of morphometry, isolated heart and aortic ring function, protein and transcriptional changes. PC:EtOH-exposed embryonic day 20 fetuses (but not postnatal offspring) had larger hearts relative to body weight. Ex vivo analysis of hearts at 5-7 months old (mo) indicated no changes in coronary function or cardiac ischaemic tolerance, and apparently improved ventricular compliance in PC:EtOH females (compared to controls). At 12 mo, vascular responses in isolated aortic rings were unaltered by PC:EtOH, whilst echocardiography revealed reduced cardiac output in female but not male PC:EtOH offspring. At 19 mo, left ventricular transcript and protein for type 1 oestrogen receptor (ESR1), HSP90 transcript and plasma oestradiol levels were all elevated in female PC:EtOH exposed offspring. Summarising, PC:EtOH adversely impacts in vivo heart function in mature female offspring, associated with increased ventricular oestrogen-related genes. PC:EtOH may thus influence age-related heart dysfunction in females through modulation of oestrogen signalling.

Early cardiac aging linked to impaired stress-resistance and transcriptional control of stress response, quality control and mitochondrial pathways

Phenotypic and transcriptomic evidence of early cardiac aging, and associated mechanisms, were investigated in young to middle-aged male mice (C57Bl/6; ages 8, 16, 32, 48 wks). Left ventricular gene expression (profiled via Illumina MouseWG-6 BeadChips), contractile and coronary function, and stress-resistance were assessed in Langendorff perfused hearts under normoxic conditions and following ischemic insult (20 min global ischemia-45 min reperfusion; I-R). Baseline or normoxic contractile function was unaltered by age, while cardiac and coronary 'reserves' (during β-adrenoceptor stimulation; 1 μM isoproterenol) declined by 48 wks. Resistance to I-R injury fell from 16 to 32 wks. Age-dependent transcriptional changes In un-stressed hearts were limited to 104 genes (>1.3-fold; 0.05 FDR), supporting: up-regulated innate defenses (glutathione and xenobiotic metabolism, chemotaxis, interleukins) and catecholamine secretion; and down-regulated extracellular matrix (ECM), growth factor and survival (PI3K/Akt) signaling. In stressed (post-ischemic) myocardium, ∼15-times as many genes (1528) were age-dependent, grouped into 6 clusters (>1.3-fold change; 0.05 FDR): most changing from 16 wks (45 % up/44 % down), a further 5 % declining from 32 wks. Major age-dependent Biological Processes in I-R hearts reveal: declining ATP metabolism, oxidative phosphorylation, cardiac contraction and morphogenesis, phospholipid metabolism and calcineurin signaling; increasing proteolysis and negative control of MAPK; and mixed changes in nuclear transport and angiogenic genes. Pathway analysis supports reductions in: autophagy, stress response, ER protein processing, mRNA surveillance and ribosome/translation genes; with later falls in mitochondrial biogenesis, oxidative phosphorylation and proteasome genes in I-R hearts. Summarizing, early cardiac aging is evident from 16 to 32 wks in male mice, characterized by: declining cardiovascular reserve and stress-resistance, transcriptomic evidence of constitutive stress and altered catecholamine and survival/growth signaling in healthy hearts; and declining stress response, quality control, mitochondrial energy metabolism and cardiac modeling processes in stressed hearts. These very early changes, potentially key substrate for advanced aging, may inform approaches to healthy aging and cardioprotection in the adult heart.

Sotagliflozin, a Dual SGLT1/2 Inhibitor, Improves Cardiac Outcomes in a Normoglycemic Mouse Model of Cardiac Pressure Overload

Selective SGLT2 inhibition reduces the risk of worsening heart failure and cardiovascular death in patients with existing heart failure, irrespective of diabetic status. We aimed to investigate the effects of dual SGLT1/2 inhibition, using sotagliflozin, on cardiac outcomes in normal diet (ND) and high fat diet (HFD) mice with cardiac pressure overload. Five-week-old male C57BL/6J mice were randomized to receive a HFD (60% of calories from fat) or remain on ND for 12 weeks. One week later, transverse aortic constriction (TAC) was employed to induce cardiac pressure-overload (50% increase in right:left carotid pressure versus sham surgery), resulting in left ventricular hypertrophic remodeling and cardiac fibrosis, albeit preserved ejection fraction. At 4 weeks post-TAC, mice were treated for 7 weeks by oral gavage once daily with sotagliflozin (10 mg/kg body weight) or vehicle (0.1% tween 80). In ND mice, treatment with sotagliflozin attenuated cardiac hypertrophy and histological markers of cardiac fibrosis induced by TAC. These benefits were associated with profound diuresis and glucosuria, without shifts toward whole-body fatty acid utilization, increased circulating ketones, nor increased cardiac ketolysis. In HFD mice, sotagliflozin reduced the mildly elevated glucose and insulin levels but did not attenuate cardiac injury induced by TAC. HFD mice had vacuolation of proximal tubular cells, associated with less profound sotagliflozin-induced diuresis and glucosuria, which suggests dampened drug action. We demonstrate the utility of dual SGLT1/2 inhibition in treating cardiac injury induced by pressure overload in normoglycemic mice. Its efficacy in high fat-fed mice with mild hyperglycemia and compromised renal morphology requires further study.

Type I Diabetes Mellitus Increases the Cardiovascular Complications of Influenza Virus Infection

People with diabetes mellitus are susceptible to both cardiovascular disease and severe influenza A virus infection. We hypothesized that diabetes also increases risks of influenza-associated cardiac complications. A murine type 1 (streptozotocin-induced) diabetes model was employed to investigate influenza-induced cardiac distress. Lung histopathology and viral titres revealed no difference in respiratory severity between infected control and diabetic mice. However, compared with infected control mice, infected diabetic mice had increased serum cardiac troponin I and creatine-kinase MB, left ventricular structural changes and right ventricular functional alterations, providing the first experimental evidence of type I diabetes increasing risks of influenza-induced cardiovascular complications.

Therapeutic Inhibition of Acid Sensing Ion Channel 1a Recovers Heart Function After Ischemia-Reperfusion Injury

Background: Ischemia-reperfusion injury (IRI) is one of the major risk factors implicated in morbidity and mortality associated with cardiovascular disease. During cardiac ischemia, the build-up of acidic metabolites results in decreased intracellular and extracellular pH that can reach as low as 6.0-6.5. The resulting tissue acidosis exacerbates ischemic injury and significantly impacts cardiac function. Methods: We used genetic and pharmacological methods to investigate the role of acid sensing ion channel 1a (ASIC1a) in cardiac IRI at the cellular and whole organ level. Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) as well as ex vivo and in vivo models of IRI were used to test the efficacy of ASIC1a inhibitors as pre- and post-conditioning therapeutic agents. Results: Analysis of human complex trait genetics indicate that variants in the ASIC1 genetic locus are significantly associated with cardiac and cerebrovascular ischemic injuries. Using hiPSC-CMs in vitro and murine ex vivo heart models, we demonstrate that genetic ablation of ASIC1a improves cardiomyocyte viability after acute IRI. Therapeutic blockade of ASIC1a using specific and potent pharmacological inhibitors recapitulates this cardioprotective effect. We used an in vivo model of myocardial infarction (MI) and two models of ex vivo donor heart procurement and storage as clinical models to show that ASIC1a inhibition improves post-IRI cardiac viability. Use of ASIC1a inhibitors as pre- or post-conditioning agents provided equivalent cardioprotection to benchmark drugs, including the sodium-hydrogen exchange inhibitor zoniporide. At the cellular and whole organ level, we show that acute exposure to ASIC1a inhibitors has no impact on cardiac ion channels regulating baseline electromechanical coupling and physiological performance. Conclusions: Collectively, our data provide compelling evidence for a novel pharmacological strategy involving ASIC1a blockade as a cardioprotective therapy to improve the viability of hearts subjected to IRI.

Stimulation of the four isoforms of receptor tyrosine kinase ErbB4, but not ErbB1, confers cardiomyocyte hypertrophy

Epidermal growth factor (EGF) receptors (ErbB1-ErbB4) promote cardiac development and growth, although the specific EGF ligands and receptor isoforms involved in growth/repair versus pathology remain undefined. We challenged ventricular cardiomyocytes with EGF-like ligands and observed that selective activation of ErbB4 (the receptor for neuregulin 1 [NRG1]), but not ErbB1 (the receptor for EGF, EGFR), stimulated hypertrophy. This lack of direct ErbB1-mediated hypertrophy occurred despite robust activation of extracellular-regulated kinase 1/2 (ERK) and protein kinase B. Hypertrophic responses to NRG1 were unaffected by the tyrosine kinase inhibitor (AG1478) at concentrations that are selective for ErbB1 over ErbB4. NRG1-induced cardiomyocyte enlargement was suppressed by small interfering RNA (siRNA) knockdown of ErbB4 and ErbB2, whereas ERK phosphorylation was only suppressed by ErbB4 siRNA. Four ErbB4 isoforms exist (JM-a/JM-b and CYT-1/CYT-2), generated by alternative splicing, and their expression declines postnatally and following cardiac hypertrophy. Silencing of all four isoforms in cardiomyocytes, using an ErbB4 siRNA, abrogated NRG1-induced hypertrophic promoter/reporter activity, which was rescued by coexpression of knockdown-resistant versions of the ErbB4 isoforms. Thus, ErbB4 confers cardiomyocyte hypertrophy to NRG1, and all four ErbB4 isoforms possess the capacity to mediate this effect.

WDR62 is required for centriole duplication in spermatogenesis and manchette removal in spermiogenesis

WDR62 is a scaffold protein involved in centriole duplication and spindle assembly during mitosis. Mutations in WDR62 can cause primary microcephaly and premature ovarian insufficiency. We have generated a genetrap mouse model deficient in WDR62 and characterised the developmental effects of WDR62 deficiency during meiosis in the testis. We have found that WDR62 deficiency leads to centriole underduplication in the spermatocytes due to reduced or delayed CEP63 accumulation in the pericentriolar matrix. This resulted in prolonged metaphase that led to apoptosis. Round spermatids that inherited a pair of centrioles progressed through spermiogenesis, however, manchette removal was delayed in WDR62 deficient spermatids due to delayed Katanin p80 accumulation in the manchette, thus producing misshapen spermatid heads with elongated manchettes. In mice, WDR62 deficiency resembles oligoasthenoteratospermia, a common form of subfertility in men that is characterised by low sperm counts, poor motility and abnormal morphology. Therefore, proper WDR62 function is necessary for timely spermatogenesis and spermiogenesis during male reproduction.

Uda Ho et al find that loss of centriolar scaffold protein WDR62 in mouse testis leads to defects in spermatogenesis. They find that WDR62 deficiency leads to centriole underduplication in spermatocytes and delayed manchette removal in spermatids due to delayed Katanin p80 accumulation.

BRET-based assay to monitor EGFR transactivation by the AT1R reveals Gq/11 protein-independent activation and AT1R-EGFR complexes

The type 1 angiotensin II (AngII) receptor (AT₁R) transactivates the epidermal growth factor receptor (EGFR), which leads to pathological remodeling of heart, blood vessels and kidney. End-point assays are used as surrogates of EGFR activation, however these downstream readouts are not applicable to live cells, in real-time. Herein, we report the use of a bioluminescence resonance energy transfer (BRET)-based assay to assess recruitment of the EGFR adaptor protein, growth factor receptor-bound protein 2 (Grb2), to the EGFR. In a variety of cell lines, both epidermal growth factor (EGF) and AngII stimulated Grb2 recruitment to EGFR. The BRET assay was used to screen a panel of 9 G protein-coupled receptors (GPCRs) and further developed for other EGFR family members (HER2 and HER3); the AT₁R was able to transactivate HER2, but not HER3. Mechanistically, AT₁R-mediated ERK1/2 activation was dependent on G_q/11 and EGFR tyrosine kinase activity, whereas the recruitment of Grb2 to the EGFR was independent of G_q/11 and only partially dependent on EGFR tyrosine kinase activity. This G_q/11 independence of EGFR transactivation was confirmed using AT₁R mutants and in CRISPR cell lines lacking G_q/11. EGFR transactivation was also apparently independent of β-arrestins. Finally, we used additional BRET-based assays and confocal microscopy to provide evidence that both AngII- and EGF-stimulation promoted AT₁R-EGFR heteromerization. In summary, we report an alternative approach to monitoring AT₁R-EGFR transactivation in live cells, which provides a more direct and proximal view of this process, including the potential for complexes between the AT₁R and EGFR.

Modeling heart failure risk in diabetes and kidney disease: limitations and potential applications of transverse aortic constriction in high-fat-fed mice

There is an increased incidence of heart failure in individuals with diabetes mellitus (DM). The coexistence of kidney disease in DM exacerbates the cardiovascular prognosis. Researchers have attempted to combine the critical features of heart failure, using transverse aortic constriction, with DM in mice, but variable findings have been reported. Furthermore, kidney outcomes have not been assessed in this setting; thus its utility as a model of heart failure in DM and kidney disease is unknown. We generated a mouse model of obesity, hyperglycemia, and mild kidney pathology by feeding male C57BL/6J mice a high-fat diet (HFD). Cardiac pressure overload was surgically induced using transverse aortic constriction (TAC). Normal diet (ND) and sham controls were included. Heart failure risk factors were evident at 8-wk post-TAC, including increased left ventricular mass (+49% in ND and +35% in HFD), cardiomyocyte hypertrophy (+40% in ND and +28% in HFD), and interstitial and perivascular fibrosis (Masson's trichrome and picrosirius red positivity). High-fat feeding did not exacerbate the TAC-induced cardiac outcomes. At 11 wk post-TAC in a separate mouse cohort, echocardiography revealed reduced left ventricular size and increased left ventricular wall thickness, the latter being evident in ND mice only. Systolic function was preserved in the TAC mice and was similar between ND and HFD. Thus combined high-fat feeding and TAC in mice did not model the increased incidence of heart failure in DM patients. This model, however, may mimic the better cardiovascular prognosis seen in overweight and obese heart failure patients.

Diastolic dysfunction is more apparent in STZ-induced diabetic female mice, despite less pronounced hyperglycemia

Diabetic cardiomyopathy is a distinct pathology characterized by early emergence of diastolic dysfunction. Increased cardiovascular risk associated with diabetes is more marked for women, but an understanding of the role of diastolic dysfunction in female susceptibility to diabetic cardiomyopathy is lacking. To investigate the sex-specific relationship between systemic diabetic status and in vivo occurrence of diastolic dysfunction, diabetes was induced in male and female mice by streptozotocin (5x daily i.p. 55 mg/kg). Echocardiography was performed at 7 weeks post-diabetes induction, cardiac collagen content assessed by picrosirius red staining, and gene expression measured using qPCR. The extent of diabetes-associated hyperglycemia was more marked in males than females (males: 25.8 ± 1.2 vs 9.1 ± 0.4 mM; females: 13.5 ± 1.5 vs 8.4 ± 0.4 mM, p < 0.05) yet in vivo diastolic dysfunction was evident in female (E/E' 54% increase, p < 0.05) but not male diabetic mice. Cardiac structural abnormalities (left ventricular wall thinning, collagen deposition) were similar in male and female diabetic mice. Female-specific gene expression changes in glucose metabolic and autophagy-related genes were evident. This study demonstrates that STZ-induced diabetic female mice exhibit a heightened susceptibility to diastolic dysfunction, despite exhibiting a lower extent of hyperglycemia than male mice. These findings highlight the importance of early echocardiographic screening of asymptomatic prediabetic at-risk patients.

Cavin-1 deficiency modifies myocardial and coronary function, stretch responses and ischaemic tolerance: roles of NOS over-activity

Caveolae and associated cavin and caveolins may govern myocardial function, together with responses to mechanical and ischaemic stresses. Abnormalities in these proteins are also implicated in different cardiovascular disorders. However, specific roles of the cavin-1 protein in cardiac and coronary responses to mechanical/metabolic perturbation remain unclear. We characterised cardiovascular impacts of cavin-1 deficiency, comparing myocardial and coronary phenotypes and responses to stretch and ischaemia-reperfusion in hearts from cavin-1 ^+/+ and cavin-1 ^-/- mice. Caveolae and caveolins 1 and 3 were depleted in cavin-1 ^-/- hearts. Cardiac ejection properties in situ were modestly reduced in cavin-1 ^-/- mice. While peak contractile performance in ex vivo myocardium from cavin-1 ^-/- and cavin-1 ^+/+ mice was comparable, intrinsic beating rate, diastolic stiffness and Frank-Starling behaviour (stretch-dependent diastolic and systolic forces) were exaggerated in cavin-1 ^-/- hearts. Increases in stretch-dependent forces were countered by NOS inhibition (100 µM L-NAME), which exposed negative inotropy in cavin-1 ^-/- hearts, and were mimicked by 100 µM nitroprusside. In contrast, chronotropic differences appeared largely NOS-independent. Cavin-1 deletion also induced NOS-dependent coronary dilatation, ≥3-fold prolongation of reactive hyperaemic responses, and exaggerated pressure-dependence of coronary flow. Stretch-dependent efflux of lactate dehydrogenase and cardiac troponin I was increased and induction of brain natriuretic peptide and c-Fos inhibited in cavin-1 ^-/- hearts, while ERK1/2 phospho-activation was preserved. Post-ischaemic dysfunction and damage was also exaggerated in cavin-1 ^-/- hearts. Diverse effects of cavin-1 deletion reveal important roles in both NOS-dependent and -independent control of cardiac and coronary functions, together with governing sarcolemmal fragility and myocardial responses to stretch and ischaemia.

Caveolin-3 plays a critical role in autophagy after ischemia-reperfusion

Autophagy is a dynamic recycling process responsible for the breakdown of misfolded proteins and damaged organelles, providing nutrients and energy for cellular renovation and homeostasis. Loss of autophagy is associated with cardiovascular diseases. Caveolin-3 (Cav-3), a muscle-specific isoform, is a structural protein within caveolae and is critical to stress adaptation in the heart. Whether Cav-3 plays a role in regulating autophagy to modulate cardiac stress responses remains unknown. In the present study, we used HL-1 cells, a cardiac muscle cell line, with stable Cav-3 knockdown (Cav-3 KD) and Cav-3 overexpression (Cav-3 OE) to study the impact of Cav-3 in regulation of autophagy. We show that traditional stimulators of autophagy (i.e., rapamycin and starvation) result in upregulation of the process in Cav-3 OE cells while Cav-3 KD cells have a blunted response. Cav-3 coimmunoprecipitated with beclin-1 and Atg12, showing an interaction of caveolin with autophagy-related proteins. In the heart, autophagy may be a major regulator of protection from ischemic stress. We found that Cav-3 KD cells have a decreased expression of autophagy markers [beclin-1, light chain (LC3-II)] after simulated ischemia and ischemia-reperfusion (I/R) compared with WT, whereas OE cells showed increased expression. Moreover, Cav-3 KD cells showed increased cell death and higher level of apoptotic proteins (cleaved caspase-3 and cytochrome c) with suppressed mitochondrial function in response to simulated ischemia and I/R, whereas Cav-3 OE cells were protected and had preserved mitochondrial function. Taken together, these results indicate that autophagy regulates adaptation to cardiac stress in a Cav-3-dependent manner.

Transcriptomic effects of adenosine 2A receptor deletion in healthy and endotoxemic murine myocardium

Influences of adenosine 2A receptor (A_2AR) activity on the cardiac transcriptome and genesis of endotoxemic myocarditis are unclear. We applied transcriptomic profiling (39 K Affymetrix arrays) to identify A_2AR-sensitive molecules, revealed by receptor knockout (KO), in healthy and endotoxemic hearts. Baseline cardiac function was unaltered and only 37 A_2AR-sensitive genes modified by A_2AR KO (≥1.2-fold change, <5 % FDR); the five most induced are Mtr, Ppbp, Chac1, Ctsk and Cnpy2 and the five most repressed are Hp, Yipf4, Acta1, Cidec and Map3k2. Few canonical paths were impacted, with altered Gnb1, Prkar2b, Pde3b and Map3k2 (among others) implicating modified G protein/cAMP/PKA and cGMP/NOS signalling. Lipopolysaccharide (LPS; 20 mg/kg) challenge for 24 h modified >4100 transcripts in wild-type (WT) myocardium (≥1.5-fold change, FDR < 1 %); the most induced are Lcn2 (+590); Saa3 (+516); Serpina3n (+122); Cxcl9 (+101) and Cxcl1 (+89) and the most repressed are Car3 (-38); Adipoq (-17); Atgrl1/Aplnr (-14); H19 (-11) and Itga8 (-8). Canonical responses centred on inflammation, immunity, cell death and remodelling, with pronounced amplification of toll-like receptor (TLR) and underlying JAK-STAT, NFκB and MAPK pathways, and a 'cardio-depressant' profile encompassing suppressed ß-adrenergic, PKA and Ca²⁺ signalling, electromechanical and mitochondrial function (and major shifts in transcripts impacting function/injury including Lcn2, S100a8/S100a9, Icam1/Vcam and Nox2 induction, and Adipoq, Igf1 and Aplnr repression). Endotoxemic responses were selectively modified by A_2AR KO, supporting inflammatory suppression via A_2AR sensitive shifts in regulators of NFκB and JAK-STAT signalling (IκBζ, IκBα, STAT1, CDKN1a and RRAS2) without impacting the cardio-depressant gene profile. Data indicate A_2ARs exert minor effects in un-stressed myocardium and selectively suppress NFκB and JAK-STAT signalling and cardiac injury without influencing cardiac depression in endotoxemia.

Cardiomyocyte Mineralocorticoid Receptor Activation Impairs Acute Cardiac Functional Recovery After Ischemic Insult

Loss of mineralocorticoid receptor signaling selectively in cardiomyocytes can ameliorate cardiac fibrotic and inflammatory responses caused by excess mineralocorticoids. The aim of this study was to characterize the role of cardiomyocyte mineralocorticoid receptor signaling in ischemia-reperfusion injury and recovery and to identify a role of mineralocorticoid receptor modulation of cardiac function. Wild-type and cardiomyocyte mineralocorticoid receptor knockout mice (8 weeks) were uninephrectomized and maintained on (1) high salt (0.9% NaCl, 0.4% KCl) or (2) high salt plus deoxycorticosterone pellet (0.3 mg/d, 0.9% NaCl, 0.4% KCl). After 8 weeks of treatment, hearts were isolated and subjected to 20 minutes of global ischemia plus 45 minutes of reperfusion. Mineralocorticoid excess increased peak contracture during ischemia regardless of genotype. Recovery of left ventricular developed pressure and rates of contraction and relaxation post ischemia-reperfusion were greater in knockout versus wild-type hearts. The incidence of arrhythmic activity during early reperfusion was significantly higher in wild-type than in knockout hearts. Levels of autophosphorylated Ca(2+)/calmodulin protein kinase II (Thr287) were elevated in hearts from wild-type versus knockout mice and associated with increased sodium hydrogen exchanger-1 expression. These findings demonstrate that cardiomyocyte-specific mineralocorticoid receptor-dependent signaling contributes to electromechanical vulnerability in acute ischemia-reperfusion via a mechanism involving Ca(2+)/calmodulin protein kinase II activation in association with upstream alteration in expression regulation of the sodium hydrogen exchanger-1.

RhoA/ROCK signaling and pleiotropic α1A-adrenergic receptor regulation of cardiac contractility

Aims

To determine the mechanisms by which the α_1A-adrenergic receptor (AR) regulates cardiac contractility.

Background

We reported previously that transgenic mice with cardiac-restricted α_1A-AR overexpression (α_1A-TG) exhibit enhanced contractility but not hypertrophy, despite evidence implicating this Gα_q/11-coupled receptor in hypertrophy.

Methods

Contractility, calcium (Ca²⁺) kinetics and sensitivity, and contractile proteins were examined in cardiomyocytes, isolated hearts and skinned fibers from α_1A-TG mice (170-fold overexpression) and their non-TG littermates (NTL) before and after α_1A-AR agonist stimulation and blockade, angiotensin II (AngII), and Rho kinase (ROCK) inhibition.

Results

Hypercontractility without hypertrophy with α_1A-AR overexpression is shown to result from increased intracellular Ca²⁺ release in response to agonist, augmenting the systolic amplitude of the intracellular Ca²⁺ concentration [Ca²⁺]_i transient without changing resting [Ca²⁺]_i. In the absence of agonist, however, α_1A-AR overexpression reduced contractility despite unchanged [Ca²⁺]_i. This hypocontractility is not due to heterologous desensitization: the contractile response to AngII, acting via its Gα_q/11-coupled receptor, was unaltered. Rather, the hypocontractility is a pleiotropic signaling effect of the α_1A-AR in the absence of agonist, inhibiting RhoA/ROCK activity, resulting in hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), reducing the Ca²⁺ sensitivity of the contractile machinery: all these effects were rapidly reversed by selective α_1A-AR blockade. Critically, ROCK inhibition in normal hearts of NTLs without α_1A-AR overexpression caused hypophosphorylation of both MYPT1 and cMLC2, and rapidly reduced basal contractility.

Conclusions

We report for the first time pleiotropic α_1A-AR signaling and the physiological role of RhoA/ROCK signaling in maintaining contractility in the normal heart.

Dysfunctional survival-signaling and stress-intolerance in aged murine and human myocardium

Changes in cytoprotective signaling may influence cardiac aging, and underpin sensitization to ischemic insult and desensitization to 'anti-ischemic' therapies. We tested whether age-dependent shifts in ischemia-reperfusion (I-R) tolerance in murine and human myocardium are associated with reduced efficacies and coupling of membrane, cytoplasmic and mitochondrial survival-signaling. Hormesis (exemplified in ischemic preconditioning; IPC) and expression of proteins influencing signaling/stress-resistance were also assessed in mice. Mouse hearts (18 vs. 2-4 mo) and human atrial tissue (75±2 vs. 55±2 yrs) exhibited profound age-dependent reductions in I-R tolerance. In mice aging negated cardioprotection via IPC, G-protein coupled receptor (GPCR) agonism (opioid, A1 and A3 adenosine receptors) and distal protein kinase c (PKC) activation (4 nM phorbol 12-myristate 13-acetate; PMA). In contrast, p38-mitogen activated protein kinase (p38-MAPK) activation (1 μM anisomycin), mitochondrial ATP-sensitive K(+) channel (mKATP) opening (50 μM diazoxide) and permeability transition pore (mPTP) inhibition (0.2 μM cyclosporin A) retained protective efficacies in older hearts (though failed to eliminate I-R tolerance differences). A similar pattern of change in protective efficacies was observed in human tissue. Murine hearts exhibited molecular changes consistent with altered membrane control (reduced caveolin-3, cholesterol and caveolae), kinase signaling (reduced p70 ribosomal s6 kinase; p70s6K) and stress-resistance (increased G-protein receptor kinase 2, GRK2; glycogen synthase kinase 3β, GSK3β; and cytosolic cytochrome c). In summary, myocardial I-R tolerance declines with age in association with dysfunctional hormesis and transduction of survival signals from GPCRs/PKC to mitochondrial effectors. Differential changes in proteins governing caveolar and mitochondrial function may contribute to signal dysfunction and stress-intolerance.

Dysfunctional survival-signaling and stress-intolerance in aged murine and human myocardium

Changes in cytoprotective signaling may influence cardiac aging, and underpin sensitization to ischemic insult and desensitization to 'anti-ischemic' therapies. We tested whether age-dependent shifts in ischemia-reperfusion (I-R) tolerance in murine and human myocardium are associated with reduced efficacies and coupling of membrane, cytoplasmic and mitochondrial survival-signaling. Hormesis (exemplified in ischemic preconditioning; IPC) and expression of proteins influencing signaling/stress-resistance were also assessed in mice. Mouse hearts (18 vs. 2-4 mo) and human atrial tissue (75±2 vs. 55±2 yrs) exhibited profound age-dependent reductions in I-R tolerance. In mice aging negated cardioprotection via IPC, G-protein coupled receptor (GPCR) agonism (opioid, A1 and A3 adenosine receptors) and distal protein kinase c (PKC) activation (4 nM phorbol 12-myristate 13-acetate; PMA). In contrast, p38-mitogen activated protein kinase (p38-MAPK) activation (1 μM anisomycin), mitochondrial ATP-sensitive K(+) channel (mKATP) opening (50 μM diazoxide) and permeability transition pore (mPTP) inhibition (0.2 μM cyclosporin A) retained protective efficacies in older hearts (though failed to eliminate I-R tolerance differences). A similar pattern of change in protective efficacies was observed in human tissue. Murine hearts exhibited molecular changes consistent with altered membrane control (reduced caveolin-3, cholesterol and caveolae), kinase signaling (reduced p70 ribosomal s6 kinase; p70s6K) and stress-resistance (increased G-protein receptor kinase 2, GRK2; glycogen synthase kinase 3β, GSK3β; and cytosolic cytochrome c). In summary, myocardial I-R tolerance declines with age in association with dysfunctional hormesis and transduction of survival signals from GPCRs/PKC to mitochondrial effectors. Differential changes in proteins governing caveolar and mitochondrial function may contribute to signal dysfunction and stress-intolerance.

Sex, sex steroids, and diabetic cardiomyopathy: making the case for experimental focus

More than three decades ago, the Framingham study revealed that cardiovascular risk is elevated for all diabetics and that this jeopardy is substantially accentuated for women in particular. Numerous studies have subsequently documented worsened cardiac outcomes for women. Given that estrogen and insulin exert major regulatory effects through common intracellular signaling pathways prominent in maintenance of cardiomyocyte function, a sex-hormone:diabetic-disease interaction is plausible. Underlying aspects of female cardiovascular pathophysiology that exaggerate cardiovascular diabetic risk may be identified, including increased vulnerability to coronary microvascular disease, age-dependent impairment of insulin-sensitivity, and differential susceptibility to hyperglycemia. Since Framingham, considerable progress has been made in the development of experimental models of diabetic disease states, including a diversity of genetic rodent models. Ample evidence indicates that animal models of both type 1 and 2 diabetes variably recapitulate aspects of diabetic cardiomyopathy including diastolic and systolic dysfunction, and cardiac structural pathology including fibrosis, loss of compliance, and in some instances ventricular hypertrophy. Perplexingly, little of this work has explored the relevance and mechanisms of sexual dimorphism in diabetic cardiomyopathy. Only a small number of experimental studies have addressed this question, yet the prospects for gaining important mechanistic insights from further experimental enquiry are considerable. The case for experimental interrogation of sex differences, and of sex steroid influences in the aetiology of diabetic cardiomyopathy, is particularly compelling-providing incentive for future investigation with ultimate therapeutic potential.

Cardiomyocyte mineralocorticoid receptors are essential for deoxycorticosterone/salt-mediated inflammation and cardiac fibrosis

Because the role of mineralocorticoid receptors in specific cell types in cardiac remodeling remains unknown, we have compared cardiac responses with deoxycorticosterone/salt in cardiomyocyte mineralocorticoid receptor-null (MyoMRKO) and wild-type (WT) mice at 8 days and 8 weeks. No differences in cardiac function between untreated WT and MyoMRKO mice were found, whereas profibrotic markers were reduced in MyoMRKO hearts at baseline. At 8 days, MyoMRKO showed monocyte/macrophage recruitment equivalent to WT mice in response to deoxycorticosterone/salt but a suppression of markers of fibrosis compared with WT. At 8 weeks, MyoMRKO mice showed no deoxycorticosterone/salt-induced increase in inflammatory cell infiltration and collagen deposition or in proinflammatory gene expression. Although some profibrotic markers were equivalently increased in both genotypes, MyoMRKO mice also showed increased baseline levels of mRNA and protein for the transforming growth factor-β/connective tissue growth factor inhibitor decorin compared with WT that was accompanied by higher levels of matrix metalloproteinase 2/matrix metalloproteinase 9 activity. These data point to a direct role for cardiomyocyte mineralocorticoid receptor in both deoxycorticosterone/salt-induced tissue inflammation and remodeling and suggest potential mechanisms for the cardioprotective effects of selective mineralocorticoid receptor blockade in cardiomyocytes that may involve regulation of matrix metalloproteinase 2/matrix metalloproteinase 9 activity and the transforming growth factor-β-connective tissue growth factor profibrotic pathway.

The adenosine A₂A receptor - myocardial protectant and coronary target in endotoxemia

BACKGROUND

Cardiac injury and dysfunction are contributors to disease progression and mortality in sepsis. This study evaluated the cardiovascular role of intrinsic A₂A adenosine receptor (A₂AAR) activity during lipopolysaccharide (LPS)-induced inflammation.

METHODS

We assessed the impact of 24 h of LPS challenge (20 mg/kg, IP) on cardiac injury, coronary function and inflammatory mediator levels in Wild-Type (WT) mice and mice lacking functional A₂AARs (A₂AAR KO).

RESULTS

Cardiac injury was evident in LPS-treated WTs, with ~7-fold elevation in serum cardiac troponin I (cTnI), and significant ventricular and coronary dysfunction. Absence of A₂AARs increased LPS-provoked cTnI release at 24 h by 3-fold without additional demise of contraction function. Importantly, A₂AAR deletion per se emulated detrimental effects of LPS on coronary function, and LPS was without effect in coronary vessels lacking A₂AARs. Effects of A₂AAR KO were independent of major shifts in circulating C-reactive protein (CRP) and haptoglobin. Cytokine responses were largely insensitive to A₂AAR deletion; substantial LPS-induced elevations (up to 100-fold) in IFN-γ and IL-10 were unaltered in A₂AAR KO mice, as were levels of IL-4 and TNF-α. However, late elevations in IL-2 and IL-5 were differentially modulated by A₂AAR KO (IL-2 reduced, IL-5 increased). Data demonstrate that in the context of LPS-triggered cardiac and coronary injury, A₂AAR activity protects myocardial viability without modifying contractile dysfunction, and selectively modulates cytokine (IL-2, IL-5) release. A₂AARs also appear to be targeted by LPS in the coronary vasculature.

CONCLUSIONS

These experimental data suggest that preservation of A₂AAR functionality might provide therapeutic benefit in human sepsis.

Aromatase deficiency confers paradoxical postischemic cardioprotection

The conventional view is that estrogen confers female cardioprotection. Estrogen synthesis depends on androgen availability, with aromatase regulating conversion of testosterone to estradiol. Extragonadal aromatase expression mediates estrogen production in some tissues, but a role for local steroid conversion has not yet been demonstrated in the heart. This study's goal was to investigate how aromatase deficiency influences myocardial function and ischemic resilience. RT-PCR analysis of C57Bl/6 mouse hearts confirmed cardiac-specific aromatase expression in adult females. Functional performance of isolated hearts from female aromatase knockout (ArKO) and aromatase wild-type mice were compared. Left ventricular developed pressures were similar in aerobic perfusion, but the maximal rate of rise of ventricular pressure was modestly reduced in ArKO hearts (3725 ± 144 vs. 4272 ± 154 mm Hg/sec, P < 0.05). After 25 min of ischemia, the recovery of left ventricular developed pressure was substantially improved in ArKO (percentage of basal at 60 min of reperfusion, 62 ± 8 vs. 30 ± 6%; P < 0.05). Hypercontracture was attenuated (end diastolic pressure, 25 ± 5 vs. 51 ± 1 mm Hg; P < 0.05), and lactate dehydrogenase content of coronary effluent was reduced throughout reperfusion in ArKO hearts. This was associated with a hyperphosphorylation of phospholamban and a reduction in phosphorylated Akt. Immediately after reperfusion, ArKO hearts exhibited increased incidence of ventricular premature beats (194 ± 70 vs. 46 ± 6, P < 0.05). These observations indicate more robust functional recovery, reduced cellular injury, and modified cardiomyocyte Ca(2+) handling in aromatase-deficient hearts. Our findings indicate that androgen-to-estrogen conversion may be of pathophysiologic importance to the heart and challenge the notion that estrogen deficiency is deleterious. These studies suggest the possibility that aromatase suppression may offer inotropic benefit in the acute ischemia/reperfusion setting with appropriate arrhythmia management.

Autophagy anomalies in the diabetic myocardium

The prominent occurrence of autophagy in fetal/neonatal myocardial tissue has been recognized for more than three decades as a key process in managing the period of perinatal nutrient deprivation. Fasting-induced autophagy has similarly been characterized as an expedient short-term cardiomyocyte response to nutrient restriction. Discerning how autophagy operates in the heart in disease contexts of substrate dysregulation is proving to be a much more complex challenge. Recent studies relating to insulin signaling and cardiac autophagy activation have provided new insights-and generated new contradictions. We highlight several anomalies and pose a number of questions, which emerge from these studies. How can myocardial autophagy induction be associated with both PtdIns3K-Akt activation (in ischemia) and suppression (in insulin resistance)? What is the explanation for the contrasting findings that myocardial autophagy is elevated in a murine model of type 2 diabetes, yet suppressed in the type 1 diabetic state? And finally, in the type 1 diabetic setting, what could be the basis for downregulated cardiac AMP-activated protein kinase (AMPK)-driven autophagic activity, when activation of this 'energy stress' kinase is usually integral to the cellular response to glucose deficit? We summarize and discuss these interesting ambiguities of myocardial autophagy regulation.

Adenosine and its receptors in the heart: regulation, retaliation and adaptation

The purine nucleoside adenosine is an important regulator within the cardiovascular system, and throughout the body. Released in response to perturbations in energy state, among other stimuli, local adenosine interacts with 4 adenosine receptor sub-types on constituent cardiac and vascular cells: A(1), A(2A), A(2B), and A(3)ARs. These G-protein coupled receptors mediate varied responses, from modulation of coronary flow, heart rate and contraction, to cardioprotection, inflammatory regulation, and control of cell growth and tissue remodeling. Research also unveils an increasingly complex interplay between members of the adenosine receptor family, and with other receptor groups. Given generally favorable effects of adenosine receptor activity (e.g. improving the balance between myocardial energy utilization and supply, limiting injury and adverse remodeling, suppressing inflammation), the adenosine receptor system is an attractive target for therapeutic manipulation. Cardiovascular adenosine receptor-based therapies are already in place, and trials of new treatments underway. Although the complex interplay between adenosine receptors and other receptors, and their wide distribution and functions, pose challenges to implementation of site/target specific cardiovascular therapy, the potential of adenosinergic pharmacotherapy can be more fully realized with greater understanding of the roles of adenosine receptors under physiological and pathological conditions. This review addresses some of the major known and proposed actions of adenosine and adenosine receptors in the heart and vessels, focusing on the ability of the adenosine receptor system to regulate cell function, retaliate against injurious stressors, and mediate longer-term adaptive responses.

Endogenous adenosine selectively modulates oxidant stress via the A1 receptor in ischemic hearts

We tested the impact of A1 adenosine receptor (AR) deletion on injury and oxidant damage in mouse hearts subjected to 25-min ischemia/45-min reperfusion (I/R). Wild-type hearts recovered approximately 50% of contractile function and released 8.2 +/- 0.7 IU/g of lactate dehydrogenase (LDH). A1AR deletion worsened dysfunction and LDH efflux (15.2 +/- 2.6 IU/g). Tissue cholesterol and native cholesteryl esters were unchanged, whereas cholesteryl ester-derived lipid hydroperoxides and hydroxides (CE-O(O)H; a marker of lipid oxidation) increased threefold, and alpha-tocopherylquinone [alpha-TQ; oxidation product of alpha-tocopherol (alpha-TOH)] increased sixfold. Elevations in alpha-TQ were augmented by two- to threefold by A1AR deletion, whereas CE-O(O)H was unaltered. A(1)AR deletion also decreased glutathione redox status ([GSH]/[GSSG + GSH]) and enhanced expression of the antioxidant response element heme oxygenase-1 (HO-1) during I/R: fourfold elevations in HO-1 mRNA and activity were doubled by A1AR deletion. Broad-spectrum AR agonism (10 microM 2-chloroadenosine; 2-CAD) countered effects of A1AR deletion on oxidant damage, HO-1, and tissue injury, indicating that additional ARs (A(2A), A(2B), and/or A3) can mediate similar actions. These data reveal that local adenosine engages A1ARs during I/R to limit oxidant damage and enhance outcome selectively. Control of alpha-TOH/alpha-TQ levels may contribute to A1AR-dependent cardioprotection.

Cardiac alpha 1-adrenergic drive in pathological remodelling

The heart is richly innervated by sympathetic nerves, and both acute and chronic regulation of cardiac function via sympathetically released catecholamines acting on cardiomyocyte adrenergic receptors (ARs), is critical for circulatory homeostasis. Cardiomyocytes express alpha 1A- and alpha 1B-, and beta 1- and beta 2-AR subtypes, which are all members of the G-protein-coupled receptor superfamily that signal via interaction with heterotrimeric G-proteins. Cardiac function - both inotropy and chronotropy - is regulated predominantly by beta 1-AR. Activation of alpha 1-ARs also results in increased contractility, as well as changes in the electrophysiological properties and metabolic responses of the heart. Nonetheless, there is little evidence that cardiac alpha 1-ARs play a major functional role under normal physiological conditions. In pathological settings, alpha 1-ARs may function in a compensatory fashion to maintain cardiac inotropy when the beta-AR system is downregulated and uncoupled from G-proteins and effectors. In addition, as we consider here, recent evidence from clinical studies and from genetically engineered animal models indicates that alpha 1-ARs are importantly involved in both developmental cardiomyocyte growth, as well as pathological hypertrophy. In the presence of pressure overload or with myocardial infarction, activation of alpha 1-ARs, particularly the alpha 1A-subtype, also appears to produce important pro-survival effects at the level of the cardiomyocyte, and to protect against maladaptive cardiac remodelling and decompensation to heart failure.

Modulation of ischaemic contracture in mouse hearts: a 'supraphysiological' response to adenosine

While inhibition of ischaemic contracture was one of the first documented cardioprotective actions of exogenously applied adenosine, it is not known whether this is a normal function of endogenous adenosine generated during ischaemic stress. Additionally, the relevance of delayed contracture to postischaemic outcome is unclear. We tested the ability of endogenous versus exogenous adenosine to modify contracture (and postischaemic outcomes) in C57/Bl6 mouse hearts. During ischaemia, untreated hearts developed peak contracture (PC) of 85 +/- 5 mmHg at 8.9 +/- 0.8 min, with time to reach 20 mmHg (time to onset of contracture; TOC) of 4.4 +/- 0.3 min. Adenosine (50 microm) delayed TOC to 6.7 +/- 0.6 min, as did pretreatment with 10 microm 2-chloroadenosine (7.2 +/- 0.5 min) or 50 nm of A(1) adenosine receptor (AR) agonist N(6)-cyclohexyladenosine (CHA) (6.7 +/- 0.3 min), but not A(2A)AR or A(3)AR agonists (20 nm 2-[4-(2-carboxyethyl) phenethylamino]-5' N-methylcarboxamidoadenosine (CGS21680) or 150 nm 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA), respectively). Adenosinergic contracture inhibition was eliminated by A(1)AR gene knockout (KO), mimicked by A(1)AR overexpression, and was associated with preservation of myocardial [ATP]. This adenosine-mediated inhibition of contracture was, however, only evident after prolonged (10 or 15 min) and not brief (3 min) pretreatment. Ischaemic contracture was also insensitive to endogenously generated adenosine, since A(1)AR KO, and non-selective and A(1)AR-selective antagonists (50 microm 8-sulphophenyltheophylline and 150 nm 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), respectively), all failed to alter intrinsic contracture development. Finally, delayed contracture with A(1)AR agonism/overexpression or ischaemic 2,3-butanedione monoxime (BDM; 5 microm to target Ca(2+) cross-bridge formation) was linked to enhanced postischaemic outcomes. In summary, adenosinergic inhibition of contracture is solely A(1)AR mediated; the response is 'supraphysiological', evident only with significant periods of pre-ischaemic AR agonism (or increased A(1)AR density); and ischaemic contracture appears insensitive to locally generated adenosine, potentially owing to the rapidity of contracture development versus the finite time necessary for expression of AR-mediated cardioprotection.

Effects of adenosine deaminase and A1 receptor deficiency in normoxic and ischaemic mouse hearts

OBJECTIVE

Adenosine deaminase (ADA) may be multifunctional, regulating adenosine levels and adenosine receptor (AR) agonism, and potentially modifying AR functionality. Herein we assess effects of ADA (and A1AR) deficiency on AR-mediated responses and ischaemic tolerance.

METHODS

Normoxic function and responses to 20 or 25 min ischaemia and 45 min reperfusion were studied in isolated hearts from wild-type mice and from mice deficient in ADA and/or A1ARs.

RESULTS

Neither ADA or A1AR deficiency significantly modified basal contractility, although ADA deficiency reduced resting heart rate (an effect abrogated by A1AR deficiency). Bradycardia and vasodilation in response to AR agonism (2-chloroadenosine) were unaltered by ADA deficiency, while A1AR deficiency eliminated the heart rate response. Adenosine efflux increased 10- to 20-fold with ADA deficiency (at the expense of inosine). Deletion of ADA improved outcome from 25 min ischaemia, reducing ventricular diastolic pressure (by 45%; 21+/-4 vs. 38+/-3mm Hg) and lactate dehydrogenase (LDH) efflux (by 40%; 0.12+/-0.01 vs. 0.21+/-0.02 U/g/min ischaemia), and enhancing pressure development (by 35%; 89+/-6 vs. 66+/-5mm Hg). Similar protection was evident after 20 min ischaemia, and was mimicked by the ADA inhibitor EHNA (5 microM). Deletion of ADA also enhanced tolerance in A1AR deficient hearts, though effects on diastolic pressure were eliminated.

CONCLUSIONS

Deficiency of ADA does not alter sensitivities of cardiovascular A1 or A2ARs (despite markedly elevated [adenosine]), but significantly improves ischaemic tolerance. Conversely, A1AR deficiency impairs ischaemic tolerance. Effects of ADA deficiency on diastolic pressure appear solely A1AR-dependent while other ARs or processes additionally contribute to improved contractile recovery and reduced cell death.

Genetic Deletion of the A 1 Adenosine Receptor Limits Myocardial Ischemic Tolerance

Adenosine receptors may be important determinants of intrinsic ischemic tolerance. Genetically modified mice were used to examine effects of global A 1 adenosine receptor (A 1 AR) knockout (KO) on function and ischemic tolerance in perfused mouse hearts. Baseline contractile function and heart rate were unaltered by A 1 AR KO, which was shown to abolish the negative chronotropic effects of 2-chloroadenosine (A 1 AR-mediated) without altering A 2 adenosine receptor–mediated coronary dilation. Tolerance to 25 minutes global normothermic ischemia (followed by 45 minutes reperfusion) was significantly limited by A 1 AR KO, with impaired contractile recovery (reduced by ≈25%) and enhanced lactate dehydrogenase (LDH) efflux (increased by ≈100%). Functional effects of A 1 AR KO involved worsened systolic pressure development with little to no change in diastolic dysfunction. In contrast, cardiac specific A 1 AR overexpression enhanced ischemic tolerance with a primary action on diastolic dysfunction. Nonselective receptor agonism (10 μmol/L 2-chloroadenosine) protected wild-type and also A 1 AR KO hearts (albeit to a lesser extent), implicating protection via subtypes additional to A 1 ARs. However, A 1 AR KO abrogated effects of 2-chloroadenosine on ischemic contracture and diastolic dysfunction. These data are the first demonstrating global deletion of the A 1 AR limits intrinsic myocardial resistance to ischemia. Data indicate the function of intrinsically activated A 1 ARs appears primarily to be enhancement of postischemic contractility and limitation of cell death.

Proximal arterial vasoconstriction precedes regression of the hyaloid vasculature

PURPOSE

To determine whether constriction of proximal arterial vessels precedes involution of the distal hyaloid vasculature in the mouse, under normal conditions, and whether this vasoconstriction is less pronounced when the distal hyaloid network persists, as it does in oxygen-induced retinopathy (OIR).

METHODS

Photomicrographs of the vasa hyaloidea propria were analysed from pre-term pups (1-2 days prior to birth), and on Days 1-11 post-birth. The OIR model involved exposing pups to approximately 90% O(2) from D1-5, followed by return to ambient air. At sampling times pups were anaesthetised and perfused with india ink. Retinal flatmounts were also incubated with FITC-lectin (BS-1, G. simplicifolia,); this labels all vessels, allowing identification of vessels not patent to the perfusate.

RESULTS

Mean diameter of proximal hyaloid vessels in pre-term pups was 25.44 +/- 1.98 microm; +/- 1 SEM). Within 3-12 hrs of birth, significant vasoconstriction was evident (diameter:12.45 +/- 0.88 microm), and normal hyaloid regression subsequently occurred. Similar vasoconstriction occurred in the O(2)-treated group, but this was reversed upon return to room air, with significant dilation of proximal vessels by D7 (diameter: 31.75 +/- 11.99 microm) and distal hyaloid vessels subsequently became enlarged and tortuous.

CONCLUSIONS

Under normal conditions, vasoconstriction of proximal hyaloid vessels occurs at birth, preceding attenuation of distal hyaloid vessels. Vasoconstriction also occurs in O(2)-treated pups during treatment, but upon return to room air, the remaining hyaloid vessels dilate proximally, and the distal vessels become dilated and tortuous. These observations support the contention that regression of the hyaloid network is dependent, in the first instance, on proximal arterial vasoconstriction.