Oral angiotensin-converting enzyme inhibitor captopril protects the heart from Porphyromonas gingivalis LPS-induced cardiac dysfunction in mice.

Although angiotensin converting enzyme (ACE) inhibitors are considered useful for the treatment of human heart failure, some experimental failing-heart models have shown little beneficial effect of ACE inhibitors in animals with poor oral health, particularly periodontitis. In this study, we examined the effects of the ACE inhibitor captopril (Cap; 0.1 mg/mL in drinking water) on cardiac dysfunction in mice treated with Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose (0.8 mg/kg/day) equivalent to the circulating level in patients with periodontal disease. Mice were divided into four groups: 1) Control, 2) PG-LPS, 3) Cap, and 4) PG-LPS + Cap. After1 week, we evaluated cardiac function by echocardiography. The left ventricular ejection fraction was significantly decreased in PG-LPS-treated mice compared to the control (from 66 ± 1.8 to 59 ± 2.5%), while Cap ameliorated the dysfunction (63 ± 1.1%). The area of cardiac fibrosis was significantly increased (approximately 2.9-fold) and the number of apoptotic myocytes was significantly increased (approximately 5.6-fold) in the heart of PG-LPS-treated group versus the control, and these changes were suppressed by Cap. The impairment of cardiac function in PG-LPS-treated mice was associated with protein kinase C δ phosphorylation (Tyr-311), leading to upregulation of NADPH oxidase 4 and xanthine oxidase, and calmodulin kinase II phosphorylation (Thr-286) with increased phospholamban phosphorylation (Thr-17). These changes were also suppressed by Cap. Our results suggest that the renin-angiotensin system might play an important role in the development of cardiac diseases induced by PG-LPS.

Effects of the angiotensin-converting enzyme inhibitor captopril on occlusal-disharmony-induced cardiac dysfunction in mice.

Occlusal disharmony is known to affect not only the oral cavity environment, but also the autonomic nervous system in the heart. Since the renin-angiotensin system (RAS) inhibitor captopril (Cap) is one of the first-line drugs for preventing cardiac remodeling in patients with heart failure, we hypothesized that Cap might prevent cardiac dysfunction induced by occlusal disharmony. Here, to test this idea, we used our bite-opening (BO) mouse model, which was developed by cementing a suitable appliance onto the mandibular incisor. Mice were divided into four groups: (1) Control, (2) BO, (3) Cap, and (4) BO + Cap. After 2 weeks, we evaluated cardiac function by echocardiography and confirmed that cardiac function was significantly decreased in the BO group compared to the control, while Cap ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and oxidative stress-induced myocardial damage in the BO group were significantly increased versus the control, and these increases were suppressed by Cap. Cardiac dysfunction induced by BO was associated with dual phosphorylation on PKCδ (Tyr-311/Thr-505), leading to activation of CaMKII with increased phosphorylation of RyR2 and phospholamban. Our results suggest that the RAS might play an important role in the development of cardiac diseases induced by occlusal anomalies.

Vidarabine, an anti-herpes agent, improves Porphyromonas gingivalis lipopolysaccharide-induced cardiac dysfunction in mice.

In this work, we examined the involvement of type 5 adenylyl cyclase (AC5) in cardiac dysfunction induced in mice given Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose equivalent to the circulating levels in periodontitis (PD) patients. Cardiac function was significantly decreased in mice given PG-LPS compared to the control, but treatment for 1 week with the AC5 inhibitor vidarabine ameliorated the dysfunction. Cardiac fibrosis and myocyte apoptosis were significantly increased in the PG-LPS group, but vidarabine blocked these changes. The PG-LPS-induced cardiac dysfunction was associated with activation of cyclic AMP/Ca2+-calmodulin-dependent protein kinase II signaling and increased phospholamban phosphorylation at threonine 17. These results suggest that pharmacological AC5 inhibition may be a promising approach to treat PD-associated cardiovascular disease.

Role of TLR4 signaling on Porphyromonas gingivalis LPS-induced cardiac dysfunction in mice.

Oral infections, particularly periodontitis, are a well-established risk factor for cardiovascular diseases, although the molecular mechanisms involved remain elusive. The aims of the present study were to investigate the effects of lipopolysaccharide derived from Porphyromonas gingivalis (PG-LPS) on cardiac function in mice, and to elucidate the underlying mechanisms. Mice (C57BL/6) were injected with PG-LPS (0.8 mg/kg/day) with or without an inhibitor of Toll-like receptor 4 (TLR4) signaling (TAK-242, 0.8 mg/kg/day) for 4 weeks. Left ventricular ejection function was significantly decreased at 1 week (from 67 ± 0.5 to 58 ± 1.2%) and remained low at 4 weeks (57 ± 1.0%). The number of apoptotic myocytes was increased (approximately 7.4-fold), the area of fibrosis was increased (approximately 3.3-fold) and the number of 8-hydroxydeoxyguanosine-positive myocytes, a sensitive indicator of oxidative DNA damage, was increased (approximately 7.6-fold) at 4 weeks in the heart of PG-LPS treated mice. However, levels of various serum pro-inflammatory cytokines in PG-LPS-treated mice were similar to those in control mice. The impairment of cardiac function in PG-LPS-treated mice appears to involve activation of TLR4-NADPH oxidase (NOX) 4 signaling, leading to abundant production of reactive oxygen species and Ca2+ leakage from sarcoplastic reticulumn induced by calmodulin kinase II (CaMKII)-mediated phosphorylation of phospholamban (at Thr-17) and ryanodine receptor 2 (at Ser-2448). Pharmacological inhibition of TLR4 with TAK-242 attenuated the changes in cardiac function in PG-LPS-treated mice. Our results indicate that TLR4-NOX4 signaling may be a new therapeutic target for treatment of cardiovascular diseases in patients with periodontitis.

Vidarabine, an anti-herpes agent, prevents occlusal-disharmony-induced cardiac dysfunction in mice.

We recently reported a positive relationship between occlusal disharmony and cardiovascular disease via activation of ß-adrenergic signaling in mice. Furthermore, inhibition of type 5 adenylyl cyclase (AC5), a major cardiac subtype in adults, protects the heart against oxidative stress. Here, we examined the role of AC5 in the development of occlusal-disharmony-induced cardiovascular disease in bite-opening (BO) mice, prepared by cementing a suitable appliance onto the mandibular incisor. We first examined the effects of BO treatment on cardiac function in mice treated or not treated for 2 weeks with vidarabine, which we previously identified as an inhibitor of cardiac AC. Cardiac function was significantly decreased in the BO group compared to the control group, but vidarabine ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but vidarabine blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as increased activation of the Ca2+-calmodulin-dependent protein kinase II/receptor-interacting protein 3 signaling pathway. These data suggest that AC5 inhibition with vidarabine might be a new therapeutic approach for the treatment of cardiovascular disease associated with occlusal disharmony.

Effects of chronic Porphylomonas gingivalis lipopolysaccharide infusion on cardiac dysfunction in mice.

OBJECTIVE: Periodontitis (PD) is a chronic inflammatory disease of tooth-supportive tissue. An association between PD and cardiovascular disease (CVD) has been established. Although PD is generally accepted as a risk factor for CVD, the existence of a relationship remains debatable. Possible mechanisms include the release of inflammatory mediators such as lipopolysaccharide (LPS), which may spread systemically and promote CVD. METHODS: To compare the effects of lipopolysaccharide derived from Porphylomonas gingivalis (PG-LPS) on cardiac muscle in mice, mice were treated for 1 week with/without PG-LPS at a dose equivalent to the circulating level in PD patients (0.8 mg/kg/day). RESULTS: Cardiac function in terms of left ventricular ejection function was significantly decreased at 1 week compared to that in the control (from 66 ± 0.5% to 57 ± 1.1%). Compared to the controls, the number of apoptotic myocytes and the area of fibrosis were significantly increased by approximately 2.7-fold and 14-fold, respectively. The impairment of cardiac function appeared to involve the activation of cAMP/PKA signaling and cAMP/calmodulin kinase II signaling (CaMKII), leading to cardiac fibrosis, myocyte apoptosis and heart failure. CONCLUSIONS: Our results indicate that cAMP/PKA and cAMP/CaMKII signaling may be a new therapeutic target for the treatment of cardiovascular diseases in patients with periodontitis.

Gender differences in eating behavior and masticatory performance: An analysis of the Three-Factor-Eating Questionnaire and its association with body mass index in healthy subjects.

OBJECTIVES: The Three-Factor-Eating Questionnaire (TFEQ) is an established instrument to assess eating behavior in terms of dietary restraint, disinhibition and hunger. METHODS: The aims of this study were to examine (1) the correlation between eating behavior and body mass index (BMI), (2) the correlation between eating behavior and masticatory performance in terms of bite size and eating speed, and (3) the effects of gender on these correlations in 56 healthy subjects (33 males [21.9 ± 2.8 years old] and 23 females [21.7 ± 2.2 years old]). RESULTS: We found a significant correlation between restraint and BMI only in females and between hunger and BMI only in males. However, disinhibition and BMI were significantly correlated in both males and females. We also found a significant correlation between bite size and hunger only in males and between eating speed and disinhibition in both males and females. CONCLUSIONS: These findings underline the importance of gender-specific counselling and behavioral treatment of obesity.

Effects of occlusal disharmony on susceptibility to atrial fibrillation in mice.

Tooth loss or incorrect positioning causes occlusal disharmony. Furthermore, tooth loss and atrial fibrillation (AF) are both risk factors for ischemic stroke and coronary heart disease. Therefore, we hypothesized that occlusal disharmony-induced stress increases susceptibility to AF, and we designed the present study to test this idea in mice. Bite-opening (BO) was done by cementing a suitable appliance onto the mandibular incisor to cause occlusal disharmony by increasing the vertical height of occlusion by 0.7 mm for a period of 2 weeks. AF susceptibility, evaluated in terms of the duration of AF induced by transesophageal burst pacing, was significantly increased concomitantly with atrial remodeling, including fibrosis, myocyte apoptosis and oxidative DNA damage, in BO mice. The BO-induced atrial remodeling was associated with increased calmodulin kinase II-mediated ryanodine receptor 2 phosphorylation on serine 2814, as well as inhibition of Akt phosphorylation. However, co-treatment with propranolol, a non-selective ß-blocker, ameliorated these changes in BO mice. These data suggest that improvement of occlusal disharmony by means of orthodontic treatment might be helpful in the treatment or prevention of AF.

Effects of occlusal disharmony on cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage in mice.

Occlusal disharmony leads to morphological changes in the hippocampus and osteopenia of the lumbar vertebra and long bones in mice, and causes stress. Various types of stress are associated with increased incidence of cardiovascular disease, but the relationship between occlusal disharmony and cardiovascular disease remain poorly understood. Therefore, in this work, we examined the effects of occlusal disharmony on cardiac homeostasis in bite-opening (BO) mice, in which a 0.7 mm space was introduced by cementing a suitable applicance onto the mandibular incisior. We first examined the effects of BO on the level of serum corticosterone, a key biomarker for stress, and on heart rate variability at 14 days after BO treatment, compared with baseline. BO treatment increased serum corticosterone levels by approximately 3.6-fold and the low frequency/high frequency ratio, an index of sympathetic nervous activity, was significantly increased by approximately 4-fold by the BO treatment. We then examined the effects of BO treatment on cardiac homeostasis in mice treated or not treated with the non-selective ß-blocker propranolol for 2 weeks. Cardiac function was significantly decreased in the BO group compared to the control group, but propranolol ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but propranolol blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as inhibition of Akt/mTOR signaling and autophagic flux. These data suggest that occlusal disharmony might affect cardiac homeostasis via alteration of the autonomic nervous system.

Role of ß-adrenergic signaling in masseter muscle.

In skeletal muscle, the major isoform of ß-adrenergic receptor (ß-AR) is ß2-AR and the minor isoform is ß1-AR, which is opposite to the situation in cardiac muscle. Despite extensive studies in cardiac muscle, the physiological roles of the ß-AR subtypes in skeletal muscle are not fully understood. Therefore, in this work, we compared the effects of chronic ß1- or ß2-AR activation with a specific ß1-AR agonist, dobutamine (DOB), or a specific ß2-AR agonist, clenbuterol (CB), on masseter and cardiac muscles in mice. In cardiac muscle, chronic ß1-AR stimulation induced cardiac hypertrophy, fibrosis and myocyte apoptosis, whereas chronic ß2-AR stimulation induced cardiac hypertrophy without histological abnormalities. In masseter muscle, however, chronic ß1-AR stimulation did not induce muscle hypertrophy, but did induce fibrosis and apoptosis concomitantly with increased levels of p44/42 MAPK (ERK1/2) (Thr-202/Tyr-204), calmodulin kinase II (Thr-286) and mammalian target of rapamycin (mTOR) (Ser-2481) phosphorylation. On the other hand, chronic ß2-AR stimulation in masseter muscle induced muscle hypertrophy without histological abnormalities, as in the case of cardiac muscle, concomitantly with phosphorylation of Akt (Ser-473) and mTOR (Ser-2448) and increased expression of microtubule-associated protein light chain 3-II, an autophagosome marker. These results suggest that the ß1-AR pathway is deleterious and the ß2-AR is protective in masseter muscle. These data should be helpful in developing pharmacological approaches for the treatment of skeletal muscle wasting and weakness.

Effects of chronic Porphyromonas gingivalis lipopolysaccharide infusion on skeletal muscles in mice.

Periodontitis, which is caused by various oral organisms, predominantly affects adults, and is one of the main causes of tooth loss, as well as leading to progression of numerous systemic diseases. However, its relationship to sarcopenia (aging-associated degenerative loss of skeletal muscle mass and function) remains unclear. The aim of this study was to investigate the effects of Porphyromonas gingivalis lipopolysaccharide (PG-LPS) on skeletal muscle in mice, and to establish the underlying mechanisms. Mice (C57BL/6) were injected with PG-LPS (0.8 mg/kg/day) for 4 weeks. This treatment significantly decreased the weight of fast-twitch skeletal muscles (masseter and tibialis anterior muscles), but not that of slow-twitch skeletal muscle (soleus muscle). The area of fibrosis was significantly increased in masseter muscle, but remained unchanged in the other two muscles. The number of apoptotic myocytes was significantly increased (approximately eightfold) in masseter muscle. These data suggest that persistent subclinical exposure to PG-LPS might reduce the size of fast-twitch skeletal muscle, but not slow-twitch skeletal muscle. Masseter muscle appears to be especially susceptible to the adverse effects of PG-LPS, because muscle remodeling (muscle fibrosis and myocyte apoptosis) was induced solely in masseter muscle. Thus, periodontitis might be one of the major causes of oral sarcopenia.

Correction to: Epac activation inhibits IL-6-induced cardiac myocyte dysfunction.

The article Epac activation inhibits IL-6-induced cardiac myocyte dysfunction.

Relationship between bite size per mouthful and dental arch size in healthy subjects.

Although multiple factors influence food bite size, the relationship between food bite size per mouthful and mandible or tongue size remains poorly understood. Here, we examined the correlations between food bite size and the lower dental arch size (an indicator of tongue size) in human subjects with good oral and general health, using fish sausage and bread as test foods. Notably, bite size of both foods was significantly positively correlated with the lower dental arch size, whereas masticatory performance (measured in terms of glucose extraction from a gummy jelly) showed no dependence on bite size. Further, bite size was significantly positively correlated with the body mass index. Our findings suggest that larger bite size is associated with larger tongue size, which might be a contributory factor to obesity.

Role of G protein-regulated inducer of neurite outgrowth 3 (GRIN3) in ß-arrestin 2-Akt signaling and dopaminergic behaviors.

The G protein-regulated inducer of neurite growth (GRIN) family has three isoforms (GRIN1-3), which bind to the Gαi/o subfamily of G protein that mediate signal processing via G protein-coupled receptors (GPCRs). Here, we show that GRIN3 is involved in regulation of dopamine-dependent behaviors and is essential for activation of the dopamine receptors (DAR)-ß-arrestin signaling cascade. Analysis of functional regions of GRIN3 showed that a di-cysteine motif (Cys751/752) is required for plasma membrane localization. GRIN3 was co-immunoprecipitated with GPCR kinases 2/6 and ß-arrestins 1/2. Among GRINs, only GRIN3, which is highly expressed in striatum, strongly interacted with ß-arrestin 2. We also generated GRIN3-knockout mice (GRIN3KO). GRIN3KO exhibited reduced locomotor activity and increased anxiety-like behavior in the elevated maze test, as well as a reduced locomoter response to dopamine stimulation. We also examined the phosphorylation of Akt at threonine 308 (phospho308-Akt), which is dephosphorylated via a ß-arrestin 2-mediated pathway. Dephosphorylation of phospho308-Akt via the D2R-ß-arrestin 2 signaling pathway was completely abolished in striatum of GRIN3KO. Our results suggest that GRIN3 has a role in recruitment and assembly of proteins involved in ß-arrestin-dependent, G protein-independent signaling.

Epac activation inhibits IL-6-induced cardiac myocyte dysfunction.

Pro-inflammatory cytokines are released in septic shock and impair cardiac function via the Jak-STAT pathway. It is well known that sympathetic and thus catecholamine signaling is activated thereafter to compensate for cardiac dysfunction. The mechanism of such compensation by catecholamine signaling has been traditionally understood to be cyclic AMP-dependent protein kinase (PKA)-mediated enforcement of cardiac contractility. We hypothesized that the exchange protein activated by cAMP (Epac), a newly identified target of cAMP signaling that functions independently of PKA, also plays a key role in this mechanism. In cultured cardiac myocytes, activation of Epac attenuated the inhibitory effect of interleukin-6 on the increase of intracellular Ca2+ concentration and contractility in response to isoproterenol, most likely through inhibition of the Jak-STAT pathway via SOCS3, with subsequent changes in inducible nitric oxide synthase expression. These findings suggest a new role of catecholamine signaling in compensating for cardiac dysfunction in heart failure. Epac and its downstream pathway may be a novel target for treating cardiac dysfunction in endotoxemia.

Cardiac overexpression of Epac1 in transgenic mice rescues lipopolysaccharide-induced cardiac dysfunction and inhibits Jak-STAT pathway.

Pro-inflammatory cytokines are released in septic shock and impair cardiac function via the Jak-STAT pathway. It is well known that sympathetic stimulation leads to coupling of the ß-adrenergic receptor/Gs/adenylyl cyclase, a membrane-bound enzyme that catalyzes the conversion of ATP to cAMP, thereby stimulating protein kinase A (PKA) and ultimately compensating for cardiac dysfunction. The mechanism of such compensation by catecholamine has been traditionally understood as PKA-mediated enforcement of cardiac contractility. We hypothesized that exchange protein activated by cyclic AMP (Epac), a new target of cAMP signaling that functions independently of protein kinase A, also plays a key role in protection against acute stresses or changes in hemodynamic overload. Lipopolysaccharide injection induced cytokine release and severe cardiac dysfunction in mouse. In mouse overexpressing Epac1 in the heart, however, the magnitude of such dysfunction was significantly smaller. Epac1 overexpression inhibited the Jak-STAT pathway, as indicated by decreased phosphorylation of STAT3 and increased SOCS3 expression, with subsequent inhibition of iNOS expression. In cultured cardiomyocytes treated with isoproterenol or forskolin, the increase of SOCS3 expression was blunted when Epac1 or PKCα was silenced with siRNA. Activation of the cAMP/Epac/PKCα pathway protected the heart against cytokine-induced cardiac dysfunction, suggesting a new role of catecholamine signaling in compensating for cardiac dysfunction in heart failure. Epac1 and its downstream pathways may be novel targets for treating cardiac dysfunction in endotoxemia.

Role of phosphodiesterase 4 expression in the Epac1 signaling-dependent skeletal muscle hypertrophic action of clenbuterol.

Clenbuterol (CB), a selective ß2-adrenergic receptor (AR) agonist, induces muscle hypertrophy and counteracts muscle atrophy. However, it is paradoxically less effective in slow-twitch muscle than in fast-twitch muscle, though slow-twitch muscle has a greater density of ß-AR We recently demonstrated that Epac1 (exchange protein activated by cyclic AMP [cAMP]1) plays a pivotal role in ß2-AR-mediated masseter muscle hypertrophy through activation of the Akt and calmodulin kinase II (CaMKII)/histone deacetylase 4 (HDAC4) signaling pathways. Here, we investigated the role of Epac1 in the differential hypertrophic effect of CB using tibialis anterior muscle (TA; typical fast-twitch muscle) and soleus muscle (SOL; typical slow-twitch muscle) of wild-type (WT) and Epac1-null mice (Epac1KO). The TA mass to tibial length (TL) ratio was similar in WT and Epac1KO at baseline and was significantly increased after CB infusion in WT, but not in Epac1KO The SOL mass to TL ratio was also similar in WT and Epac1KO at baseline, but CB-induced hypertrophy was suppressed in both mice. In order to understand the mechanism involved, we measured the protein expression levels of ß-AR signaling-related molecules, and found that phosphodiesterase 4 (PDE4) expression was 12-fold greater in SOL than in TA These results are consistent with the idea that increased PDE4-mediated cAMP hydrolysis occurs in SOL compared to TA, resulting in a reduced cAMP concentration that is insufficient to activate Epac1 and its downstream Akt and CaMKII/HDAC4 hypertrophic signaling pathways in SOL of WT This scenario can account for the differential effects of CB on fast- and slow-twitch muscles.

Effects of food diameter on bite size per mouthful and chewing behavior.

Obesity is well known to be associated with a wide variety of illnesses, and is an increasing problem not only in developed countries but also in developing countries. It is well known that large bite size contributes to excess energy intake and obesity, whereas an increased number of chews before swallowing the food bolus is associated with suppression of obesity. However, the effect of food diameter on bite size per mouthful and on chewing behavior remains poorly understood. Here, we examined the effects of food diameter on bite size and chewing behavior using a masticatory counter during the mastication of stick-type biscuits having the same length (10 cm) and ingredients, but with four different diameters (3.0, 3.5, 4.0, and 8.0 mm). Bite length and bite weight per mouthful were similar among the 3.0, 3.5, and 4.0 mm groups. However, bite length in the 8.0 mm group was significantly smaller, whereas bite weight was significantly greater than in the 3.0/3.5 mm groups. Further, the number of chews gradually increased, whereas the number of chews per bite weight gradually decreased, with an increase of biscuit diameter. These results indicate that a smaller biscuit diameter is associated with a smaller bite weight per mouthful and a greater number of chews per bite weight. This is the first report to quantity the effect of food diameter on bite weight per mouthful and on chewing behavior; these results should be helpful in the design of effective, safe, and low-cost behavioral modification therapy to combat obesity.

Protective Effects of Clenbuterol against Dexamethasone-Induced Masseter Muscle Atrophy and Myosin Heavy Chain Transition.

BACKGROUND: Glucocorticoid has a direct catabolic effect on skeletal muscle, leading to muscle atrophy, but no effective pharmacotherapy is available. We reported that clenbuterol (CB) induced masseter muscle hypertrophy and slow-to-fast myosin heavy chain (MHC) isoform transition through direct muscle ß2-adrenergic receptor stimulation. Thus, we hypothesized that CB would antagonize glucocorticoid (dexamethasone; DEX)-induced muscle atrophy and fast-to-slow MHC isoform transition. METHODOLOGY: We examined the effect of CB on DEX-induced masseter muscle atrophy by measuring masseter muscle weight, fiber diameter, cross-sectional area, and myosin heavy chain (MHC) composition. To elucidate the mechanisms involved, we used immunoblotting to study the effects of CB on muscle hypertrophic signaling (insulin growth factor 1 (IGF1) expression, Akt/mammalian target of rapamycin (mTOR) pathway, and calcineurin pathway) and atrophic signaling (Akt/Forkhead box-O (FOXO) pathway and myostatin expression) in masseter muscle of rats treated with DEX and/or CB. RESULTS AND CONCLUSION: Masseter muscle weight in the DEX-treated group was significantly lower than that in the Control group, as expected, but co-treatment with CB suppressed the DEX-induced masseter muscle atrophy, concomitantly with inhibition of fast-to-slow MHC isoforms transition. Activation of the Akt/mTOR pathway in masseter muscle of the DEX-treated group was significantly inhibited compared to that of the Control group, and CB suppressed this inhibition. DEX also suppressed expression of IGF1 (positive regulator of muscle growth), and CB attenuated this inhibition. Myostatin protein expression was unchanged. CB had no effect on activation of the Akt/FOXO pathway. These results indicate that CB antagonizes DEX-induced muscle atrophy and fast-to-slow MHC isoform transition via modulation of Akt/mTOR activity and IGF1 expression. CB might be a useful pharmacological agent for treatment of glucocorticoid-induced muscle atrophy.

Coupling of ß1-adrenergic receptor to type 5 adenylyl cyclase and its physiological relevance in cardiac myocytes.

Myocardial ß-adrenergic receptor (ß-AR) ß1- and ß2-subtypes are highly homologous, but play opposite roles in cardiac apoptosis and heart failure, as do cardiac adenylyl cyclase (AC) subtypes 5 (AC5) and 6 (AC6): ß1-AR and AC5 promote cardiac remodeling, while ß2-AR and AC6 activate cell survival pathways. However, the mechanisms involved remain poorly understood. We hypothesized that AC5 is coupled preferentially to ß1-AR rather than ß2-AR, and we examined this idea by means of pharmacological and genetic approaches. We found that selective inhibition of AC5 with 2'5'-dideoxyadenosine significantly suppressed cAMP accumulation and cardiac apoptosis induced by selective ß1-AR stimulation, but had no effect on cAMP accumulation and cardiac apoptosis in response to selective ß2-AR stimulation. The results of selective stimulation of ß1-AR and ß2-AR in neonatal cardiac myocytes prepared from wild-type and AC5-knockout mice were also consistent with the idea that ß1-AR selectively couples with AC5. We believe these results are helpful for understanding the mechanisms underlying the different roles of AR subtypes in healthy and diseased hearts.