β3肾上腺素受体调控一氧化氮在心血管系统中的作用

研究发现心血管系统中β3-肾上腺素受体（β3-adrenergic receptor,β3-AR）发挥着与传统的β1-/β2-AR不同的交感神经调节作用。虽然β3-AR在心血管系统中的作用还有争议,但越来越多的证据显示其在交感神经系统过度兴奋时能够发挥类似“刹车”的心脏保护作用。β3-AR在儿茶酚胺浓度增高时激活,通过调节一氧化氮合酶影响一氧化氮（NO）生成,进而产生负性肌力作用。本文对心血管系统中β3-AR调控NO的研究进展作一综述。     

Beta 3-adrenoreceptor regulation of nitric oxide in the cardiovascular system

The presence of a third β-adrenergic receptor (β3-AR) in the cardiovascular system has challenged the classical paradigm of sympathetic regulation by β1- and β2-adrenergic receptors. While β3-AR's role in the cardiovascular system remains controversial, increasing evidence suggests that it serves as a “brake” in sympathetic overstimulation — it is activated at high catecholamine concentrations, producing a negative inotropic effect that antagonizes β1- and β2-AR activity. The anti-adrenergic effects induced by β3-AR were initially linked to nitric oxide (NO) release via endothelial NO synthase (eNOS), although more recently it has been shown under some conditions to increase NO production in the cardiovascular system via the other two NOS isoforms, namely inducible NOS (iNOS) and neuronal NOS (nNOS). We summarize recent findings regarding β3-AR effects on the cardiovascular system and explore its prospective as a therapeutic target, particularly focusing on its emerging role as an important mediator of NO signaling in the pathogenesis of cardiovascular disorders.     

Phospholemman is a negative feed-forward regulator of Ca2+ in β-adrenergic signaling, accelerating β-adrenergic inotropy

Sympathetic stimulation enhances cardiac contractility by stimulating β-adrenergic signaling and protein kinase A (PKA). Recently, phospholemman (PLM) has emerged as an important PKA substrate capable of regulating cytosolic Ca(2+) transients. However, it remains unclear how PLM contributes to β-adrenergic inotropy. Here we developed a computational model to clarify PLM's role in the β-adrenergic signaling response. Simulating Na(+) and sarcoplasmic reticulum (SR) Ca(2+) clamps, we identify an effect of PLM phosphorylation on SR unloading as the key mechanism by which PLM confers cytosolic Ca(2+) adaptation to long-term β-adrenergic receptor (β-AR) stimulation. Moreover, we show that phospholamban (PLB) opposes and overtakes these actions on SR load, forming a negative feed-forward loop in the β-adrenergic signaling cascade. This network motif dominates the negative feedback conferred by β-AR desensitization and accelerates β-AR-induced inotropy. Model analysis therefore unmasks key actions of PLM phosphorylation during β-adrenergic signaling, indicating that PLM is a critical component of the fight-or-flight response.     

cAMP-mediated beta-adrenergic signaling negatively regulates Gq-coupled receptor-mediated fetal gene response in cardiomyocytes

The treatment with β-blockers causes an enhancement of the norepinephrine-induced fetal gene response in cultured cardiomyocytes. Here, we tested whether the activation of cAMP-mediated β-adrenergic signaling antagonizes α₁-adrenergic receptor (AR)-mediated fetal gene response. To address this question, the fetal gene program, of which atrial natriuretic peptide (ANP) and the β-isoform of myosin heavy chain are classical members, was induced by phenylephrine (PE), an α₁-AR agonist. In cultured neonatal rat cardiomyocytes, we found that stimulation of β-ARs with isoproterenol, a β-AR agonist, inhibited the fetal gene expression induced by PE. Similar results were also observed when cardiomyocytes were treated with forskolin (FSK), a direct activator of adenylyl cyclase, or 8-CPT-6-Phe-cAMP, a selective activator of protein kinase A (PKA). Conversely, the PE-induced fetal gene expression was further upregulated by H89, a selective PKA inhibitor. To evaluate whether these results could be generalized to Gq-mediated signaling and not specifically to α₁-ARs, cardiomyocytes were treated with prostaglandin F₂α, another Gq-coupled receptor agonist, which is able to promote fetal gene expression. This treatment caused an increase of both ANP mRNA and protein levels, which was almost completely abolished by FSK treatment. The capability of β-adrenergic signaling to regulate the fetal gene expression was also evaluated in vivo conditions by using β1- and β2-AR double knockout mice, in which the predominant cardiac β-AR subtypes are lacking, or by administering isoproterenol (ISO), a β-AR agonist, at a subpressor dose. A significant increase of the fetal gene expression was found in β₁- and β₂-AR gene deficient mice. Conversely, we found that ANP, β-MHC and skACT mRNA levels were significantly decreased in ISO-treated hearts. Collectively, these data indicate that cAMP-mediated β-adrenergic signaling negatively regulates Gq cascade activation-induced fetal gene expression in cultured cardiomyocytes and that this inhibitory regulation is already operative in the mouse heart under physiological conditions.     

Hyperglycemia enhances adipogenic induction of lipid accumulation: involvement of extracellular signal-regulated protein kinase 1/2, phosphoinositide 3-kinase/Akt, and peroxisome proliferator-activated receptor gamma signaling

The molecular events of hyperglycemia-triggered increase in adipogenic induction of lipid accumulation remain unclear. We examined the effects of hyperglycemia on adipogenic induction of lipid accumulation and its involved signaling molecules, such as phosphoinositide 3-kinase (PI3K), ERKs, and peroxisome proliferator-activated receptor gamma (PPAR gamma). Bone marrow-derived mesenchymal stem cells (MSCs) isolated from FVB/N mice were capable of differentiating into adipocytes in adipogenic medium. The effects of high glucose (HG) (25.5 mm) were assessed in vitro by RT-PCR, ELISA, flow cytometry, immunostaining, and immunoblotting. The in vivo effect of hyperglycemia was further studied in streptozotocin (STZ)-induced diabetic FVB/N mice. Exposure of MSCs to HG enhanced adipogenic induction of lipid accumulation as compared with 5.5 mm glucose. HG increased PPAR gamma expression and PI3K activity and its downstream effector Akt phosphorylation during adipogenesis. Inhibition of PI3K/Akt activity with PI3K inhibitor LY294002 or by expressing the dominant negative p85 or Akt prevented the HG-enhanced PPAR gamma-dependent adipogenic induction of lipid accumulation. Moreover, HG increased the phosphorylation of ERK1/2 during adipogenesis. MAPK/ERK inhibitor PD98059 inhibited the PI3K activity, Akt phosphorylation, and lipid accumulation triggered by HG. PI3K inhibitor LY294002 did not affect the HG-increased ERK1/2 phosphorylation during adipogenesis. We next observed that adipogenic induction of lipid accumulation of MSCs isolated from STZ-induced diabetic mice is enhanced. Moreover, triglyceride, PPAR gamma expression, phosphorylated Akt and ERK1/2, and marrow fat in bones of STZ-diabetic mice were also increased. These results suggest that hyperglycemia enhances the adipogenic induction of lipid accumulation through an ERK1/2-activated PI3K/Akt-regulated PPAR gamma pathway.     

Role of β-adrenergic receptors in regulation of hepatic fat accumulation during aging

Excessive fat accumulation in liver (hepatic steatosis) predisposes to hepatic functional and structural impairment and overall metabolic risk. Previous studies noted an association between hepatic steatosis and age in humans and rodents. However, the mechanisms leading to age-associated hepatic fat accumulation remain unknown. Earlier work from our group showed that β-adrenergic receptor (β-AR) levels and β-AR-stimulated adenylyl cyclase activity increase in rat liver during aging. Here we investigated whether age-associated increases in β-AR signaling play a role in augmenting hepatic lipid accumulation. We demonstrate an increase in hepatic lipid content during senescence and a significant correlation between hepatic fat content and stimulation of adenylyl cyclase activity by the β-AR agonist isoproterenol in rat liver. Isoproterenol administration to young and old rodents in vivo increased hepatic lipid accumulation. Furthermore, in vitro overexpression of β1- and β2-AR subtypes in hepatocytes from young rodents increased cellular lipid content, whereas inhibition of β-ARs by receptor subtype-specific inhibitors reduced lipid levels in hepatocytes from senescent animals. Isoproterenol-induced hepatic lipid accumulation in vivo was prevented by the β-AR nonselective blocker propranolol, suggesting a novel therapeutic effect of this class of drugs in hepatic steatosis. Acipimox, which inhibits adipose tissue lipolysis, did not alter isoproterenol-mediated hepatic fat accumulation; thus β-AR responsive hepatic lipid accumulation does not appear to be related primarily to altered lipolysis. These findings suggest that augmented hepatic β-AR signaling during aging may increase lipid accumulation in liver and advocate a possible role for β-adrenergic blockers in preventing or retarding the development of hepatic steatosis.     

多囊卵巢综合征妇女的β-3-肾上腺素能受体基因与胰岛素抵抗的关系

目的探讨β     

Beta1-adrenergic receptors promote focal adhesion signaling downregulation and myocyte apoptosis in acute volume overload

Numerous studies demonstrated increased expression of extracellular matrix (ECM) proteins and activation of focal adhesion (FA) signaling pathways in models of pressure overload-induced cardiac hypertrophy. However, little is known about FA signaling in response to volume overload where cardiac hypertrophy is associated with ECM loss. This study examines the role of beta1-adrenergic receptors (β(1)-ARs) in FA signaling changes and myocyte apoptosis induced during acute hemodynamic stress of volume overload. Rats with eccentric cardiac hypertrophy induced after aorto-caval fistula (ACF) develop reduced interstitial collagen content and decreased tyrosine phosphorylation of key FA signaling molecules FAK, Pyk(2) and paxillin along with an increase in cardiac myocyte apoptosis. ACF also increased activation of PTEN, a dual lipid and protein phosphatase, and its interaction with FA proteins. β(1)-AR blockade (extended-release of metoprolol succinate, 100mg QD) markedly attenuated PTEN activation, restored FA signaling and reduced myocyte apoptosis induced by ACF at 2days, but failed to reduce interstitial collagen loss and left ventricular dilatation. Treating cultured myocytes with β(1)-AR agonists or adenoviral expression of β(1)-ARs caused PTEN activation and interaction with FA proteins, thus leading to FA signaling downregulation and myocyte apoptosis. Adenoviral-mediated expression of a catalytically inactive PTEN mutant or wild-type FAK restored FA signaling downregulation and attenuated myocyte apoptosis induced by β(1)-ARs. Collectively, these data show that β(1)-AR stimulation in response to ACF induces FA signaling downregulation through an ECM-independent mechanism. This effect involves PTEN activation and may contribute to adverse cardiac remodeling and function in the course of volume overload.     

Taking the heart failure battle inside the cell: small molecule targeting of Gβγ subunits

Heart failure (HF) is devastating disease with poor prognosis. Elevated sympathetic nervous system activity and outflow, leading to pathologic attenuation and desensitization of β-adrenergic receptors (β-ARs) signaling and responsiveness, are salient characteristic of HF progression. These pathologic effects on β-AR signaling and HF progression occur in part due to Gβγ-mediated signaling, including recruitment of receptor desensitizing kinases such as G-protein coupled receptor (GPCR) kinase 2 (GRK2) and phosphoinositide 3-kinase (PI3K), which subsequently phosphorylate agonistoccupied GPCRs. Additionally, chronic GPCR signaling signals chronically dissociated Gβγ subunits to interact with multiple effector molecules that activate various signaling cascades involved in HF pathophysiology. Importantly, targeting Gβγ signaling with large peptide inhibitors has proven a promising therapeutic paradigm in the treatment of HF. We recently described an approach to identify small molecule Gβγ inhibitors that selectively block particular Gβγ functions by specifically targeting a Gβγ protein-protein interaction "hot spot." Here we describe their effects on Gβγ downstream signaling pathways, including their role in HF pathophysiology. We suggest a promising therapeutic role for small molecule inhibition of pathologic Gβγ signaling in the treatment of HF. This article is part of a special issue entitled “Key Signaling Molecules in Hypertrophy and Heart Failure.”     

β1肾上腺素受体失敏在心脏疾病中的研究进展

β肾上腺素受体（β-AR）,属于G蛋白耦联受体超家族成员,在快速调节心脏功能中发挥着重要的作用。由于交感神经系统激活,儿茶酚胺持续作用,β-AR广泛参与外周血液循环、代谢调控、肌肉收缩以及中枢神经活动。在心肌细胞中,存在三种亚型：β1-AR、β2-AR和133-AR。β1-AR是其中最主要的一种受体亚型,它在儿茶酚胺所引起的正性变时和变力效应中起主要作用。B-AR的失敏包括其数量的下调,以及功能的下降。现主要探讨β1-AR失敏与心脏疾病的关系,为心脏疾病的治疗提供一定的理论依据。为后续的深入研究奠定基础。     

A novel role for an endothelial adrenergic receptor system in mediating catecholestradiol-induced proliferation of uterine artery endothelial cells

Sequential conversion of estradiol-17β to its biologically active catecholestradiols, 2-hydroxyestradiol (OHE(2)) and 4-OHE(2), contributes importantly to its angiogenic effects on uterine artery endothelial cells (UAECs) derived from pregnant, but not nonpregnant ewes via an estrogen receptor-independent mechanism. Because catecholestradiols and catecholamines exhibit structural similarities and have high affinity for α- and β-adrenergic receptors (ARs), we investigated whether the endothelial α- or β-ARs mediate catecholestradiol-induced proliferation of P-UAECs and whether catecholamines alter these responses. Western analyses revealed expression of specific AR subtypes in nonpregnant UAECs and P-UAECs, including α(2)-, β(2)-, and β(3)-ARs but not α(1)- and β(1)-ARs. Levels of β(2)-ARs and β(3)-ARs were unaltered by pregnancy, whereas α(2)-ARs were decreased. Norepinephrine and epinephrine increased P-UAEC, but not nonpregnant UAEC proliferation, and these effects were suppressed by propranolol (β-AR blocker) but not phentolamine (α-AR blocker). Catecholamines combinations with 2-OHE(2) or 4-OHE(2) enhanced P-UAEC mitogenesis. Catecholestradiol-induced P-UAEC proliferation was also inhibited by propranolol but not phentolamine. β(2)-AR and β(3)-AR antagonists (ICI 118 551and SR 59230A, respectively) abrogated the mitogenic effects of both 2-OHE(2) and 4-OHE(2). Stimulation of β(2)-ARs and β(3)-ARs using formoterol and BRL 37344 dose-dependently stimulated P-UAEC proliferation, which was abrogated by ICI 118 551 and SR 59230A, respectively. Proliferation effects of both catecholamines and catecholestradiols were only observed in P-UAECs (not nonpregnant UAECs) and were mediated via β(2)-ARs and β(3)-ARs. We demonstrate for the first time convergence of the endothelial AR and estrogenic systems in regulating endothelial proliferation, thus providing a distinct evolutionary advantage for modulating uterine perfusion during stressful pregnancies.     

β_2-肾上腺素受体亚型激动对于血管平滑肌细胞增殖的影响

目的研究β2-肾上腺素受体亚型(beta2-adrenergic receptor,β2-AR)激动对于血管平滑肌细胞(VSMC)增殖的调控效应。方法应用携带重组β2-AR片段的腺病毒感染VSMC制备受体过表达模型。分别应用Zinterol(ZIN)以及异丙基肾上腺素(ISO)刺激生理状态和β2-AR过表达的平滑肌细胞后,采用四甲基偶氮唑盐(MTT)比色法和细胞计数法检测吸光度(A,曾称光密度OD)值和细胞数目的改变。结果ZIN刺激1天时A值开始下降(P<0.05),3天时抑制作用达高峰,抑制率为(32.00±1.62)%。细胞计数法测得ZIN激动3天时细胞数为对照组的(69.29±9.26)%。应用CGP20712A阻断β1-AR激活后,非选择性-βAR激动剂ISO刺激细胞后得到结果相似。特异性β2-AR拮抗剂ICI 118,551可逆转此抑制效应。ISO刺激过表达的β2-AR 3天时MTT检测结果相似。结论β2-AR亚型激动可抑制VSMC的增殖。     

心力衰竭心肌β3肾上腺素能受体与氧化应激关系的实验研究

目的 研究心力衰竭(心衰)大鼠心肌β3,肾上腺素能受体(β3-AR)变化,观察选择性β3-AR抑制剂(SR59230A)对β3-AR、氧化应激状态的影响.方法 将异丙肾上腺素(ISO)诱导的心衰大鼠随机分成ISO组(18只)与ISO+SR59230A组(21只),同时以正常大鼠为对照组(7只).ISO+SR59230A组给予SR59230A,每日2次腹腔注射;ISO组给予相应生理盐水1 ml;对照组不予处置.6周后测定心功能、心肌β3-AR、内皮型一氧化氮合酶(eNOS)、小三磷酸鸟苷结合蛋白(Racl)mRNA、蛋白表达及脂质过氧化物(LPO)、总超氧化物歧化酶(T-SOD)指标.结果 心衰大鼠心功能恶化,心肌β3-AR mRNA表达增加,SR59230A可改善心功能,降低β3-AR mRNA表达(均为P<0.05).心衰时,eNOS、Racl mRNA及蛋白上调,LPO产生增加、T-SOD水平降低.SR59230A降低eNOS、Racl表达,增加心肌组织T-SOD水平,使LPO减少(均为P<0.05).结论 心衰时,β3-AR表达增加,加重心肌氧化应激反应,恶化心功能.β3-AR抑制剂改善心功能可能通过抑制氧化应激、延缓心衰进展来实现.     

Local renin angiotensin expression regulates human mesenchymal stem cell differentiation to adipocytes

Clinical and experimental evidence suggest that the renin-angiotensin system (RAS) plays a role in metabolic syndrome. Adipogenesis is suggested to modulate obesity and obesity-related consequences, such as metabolic syndrome. Although mesenchymal stem cells (MSCs) are a major source of adipocyte generation, the influence of RAS on MSC differentiation to adipocyte is unknown. We evaluated the expression of endogenous RAS in human MSCs during its differentiation to adipocytes and studied the effects of angiotensin II (Ang II), Ang II type 1 receptor blocker Valsartan, and type 2 (AT(2)) receptor blocker PD123319. Our data showed that differentiation was associated with an increase in cellular renin and AT(2) receptor expression and a concomitant decrease in angiotensinogen and angiotensin-converting enzyme expression. The net effect is an increase in endogenous cellular angiotensin II production. Incubation with Ang II (exogenous) inhibited adipogenesis. Combined treatment of exogenous Ang II and Valsartan further inhibited adipogenesis, whereas combined treatment of Ang II and PD123319 completely abolished the inhibition of adipogenesis, suggesting an important role for the AT(2) receptor. Blockade of endogenous angiotensin II effect by incubation with Valsartan alone inhibited adipogenesis, whereas PD123319 alone promoted adipogenesis, confirming the data using exogenous Ang II. The combination of Valsartan and PD123319 had no net effect. Our data demonstrate an important role of the expression of the local RAS in the regulation of human MSC differentiation to adipocytes. Elucidation of the molecular mechanism should provide important insight into the pathophysiology of the metabolic syndrome and the development of future therapeutics.     

Toll-like receptors and their ligands control mesenchymal stem cell functions.

Mesenchymal stem cells (MSCs) are widespread in adult organisms and may be involved in tissue maintenance and repair as well as in the regulation of hematopoiesis and immunologic responses. Thus, it is important to discover the factors controlling MSC renewal and differentiation. Here we report that adult MSCs express functional Toll-like receptors (TLRs), confirmed by the responses of MSCs to TLR ligands. Pam3Cys, a prototypic TLR-2 ligand, augmented interleukin-6 secretion by MSC, induced nuclear factor kappa B (NF-kappaB) translocation, reduced MSC basal motility, and increased MSC proliferation. The hallmark of MSC function is the capacity to differentiate into several mesodermal lineages. We show herein that Pam3Cys inhibited MSC differentiation into osteogenic, adipogenic, and chondrogenic cells while sparing their immunosuppressive effect. Our study therefore shows that a TLR ligand can antagonize MSC differentiation triggered by exogenous mediators and consequently maintains the cells in an undifferentiated and proliferating state in vitro. Moreover, MSCs derived from myeloid factor 88 (MyD88)-deficient mice lacked the capacity to differentiate effectively into osteogenic and chondrogenic cells. It appears that TLRs and their ligands can serve as regulators of MSC proliferation and differentiation and might affect the maintenance of MSC multipotency.