ß2-AR blockade potentiates MEK1/2 inhibitor effect on HNSCC by regulating the Nrf2-mediated defense mechanism.

The ß2-Adrenergic receptor (ß2-AR) is a G protein-coupled receptor (GPCR), involved in the development of many cancers, among which HNSCC. In this contest, ß2-AR signaling interacts with different pathways, such as PI3K and MAPK, commonly activated by TK receptors. For this reason, TK blockade is one of the most adopted therapeutic strategies in HNSCC patients. In our study we investigated the effects of the ß2-AR blocking in HNSCC cell lines, using the selective inhibitor ICI118,551 (ICI), in combination with the MAPK inhibitor U0126. We found that ICI leads to the blocking of p38 and NF-kB oncogenic pathways, strongly affecting also the ERK and PI3K pathways. Cotreatment with U0126 displays a synergic effect on cell viability and pathway alteration. Interestingly, we found that the ß2-AR blockade affects Nrf2-Keap1 stability and its nuclear translocation leading to a drastic ROS increase and oxidative stress. Our results are confirmed by a TCGA dataset analysis, showing that NFE2L2 gene is commonly overexpressed in HNSC, and correlated with a lower survival rate. In our system, the PI3K pathway inhibition culminated in the blocking of pro-survival autophagy, a mechanism normally adopted by cancer cells to became less responsive to the therapies. The mTOR expression, commonly upregulated in HNSC, was reduced in patients with disease-recurrence. It is well known that mTOR has a strong autophagy inhibition effect, therefore its downregulation promoted pro-survival autophagy, with a related increase recurrence rate. Our findings highlight for the first time the key role of ß2-AR and related pathway in HNSCC cell proliferation and drug resistance, proposing it as a valuable therapeutic molecular target.

Methylglyoxal Impairs ß2-Adrenoceptor-Mediated Vasodilatory Mechanisms in Rat Retinal Arterioles.

Methylglyoxal, a highly reactive dicarbonyl compound, is formed as a by-product of glycolysis and plays an important role in the pathogenesis of diabetic complications, including diabetic retinopathy. However, it remains to be determined how methylglyoxal affects the regulatory mechanisms of retinal blood flow. In this study, we examined the effects of methylglyoxal on ß2-adrenoceptor-mediated vasodilatory mechanisms in rat retinal arterioles. The retinal vasodilator responses were assessed by measuring the diameter of retinal arterioles in the fundus images. Intravitreal injection of methylglyoxal significantly diminished the vasodilation of retinal arterioles induced by the ß2-adrenoceptor agonist salbutamol. The vasodilator effect of BMS-191011, a large-conductance Ca2+-activated K+ (BKCa) channel opener, on retinal arterioles was also attenuated by methylglyoxal. In contrast, methylglyoxal had no significant effect on retinal vasodilator response to forskolin. Methylglyoxal attenuated retinal vasodilator response to salbutamol under blockade of BKCa channels with iberiotoxin, an inhibitor of the channels. These results suggest that methylglyoxal attenuates ß2-adrenoceptor-mediated retinal vasodilation by impairing the coupling of the ß2-adrenoceptor to the guanine nucleotide-binding protein (Gs protein) and the function of the BKCa channel. Increased methylglyoxal in the eyes may contribute to the impairment of regulatory mechanisms of retinal blood flow in patients with diabetic retinopathy.

ß2-Adrenergic receptor-dependent attenuation of hypoxic pulmonary vasoconstriction prevents progression of pulmonary arterial hypertension in intermittent hypoxic rats.

In sleep apnea syndrome (SAS), intermittent hypoxia (IH) induces repeated episodes of hypoxic pulmonary vasoconstriction (HPV) during sleep, which presumably contribute to pulmonary arterial hypertension (PAH). However, the prevalence of PAH was low and severity is mostly mild in SAS patients, and mild or no right ventricular hypertrophy (RVH) was reported in IH-exposed animals. The question then arises as to why PAH is not a universal finding in SAS if repeated hypoxia of sufficient duration causes cycling HPV. In the present study, rats underwent IH at a rate of 3 min cycles of 4-21% O2 for 8 h/d for 6 w. Assessment of diameter changes in small pulmonary arteries in response to acute hypoxia and drugs were performed using synchrotron radiation microangiography on anesthetized rats. In IH-rats, neither PAH nor RVH was observed and HPV was strongly reversed. Nadolol (a hydrophilic ß(1, 2)-blocker) augmented the attenuated HPV to almost the same level as that in N-rats, but atenolol (a hydrophilic ß1-blocker) had no effect on the HPV in IH. These ß-blockers had almost no effect on the HPV in N-rats. Chronic administration of nadolol during 6 weeks of IH exposure induced PAH and RVH in IH-rats, but did not in N-rats. Meanwhile, atenolol had no effect on morphometric and hemodynamic changes in N and IH-rats. Protein expression of the ß1-adrenergic receptor (AR) was down-regulated while that of ß2AR was preserved in pulmonary arteries of IH-rats. Phosphorylation of p85 (chief component of phosphoinositide 3-kinase (PI3K)), protein kinase B (Akt), and endothelial nitric oxide synthase (eNOS) were abrogated by chronic administration of nadolol in the lung tissue of IH-rats. We conclude that IH-derived activation of ß2AR in the pulmonary arteries attenuates the HPV, thereby preventing progression of IH-induced PAH. This protective effect may depend on the ß2AR-Gi mediated PI3K/Akt/eNOS signaling pathway.

Blocking of ß-adrenergic receptors during the subfertile period inhibits spontaneous ovarian cyst formation in rats.

As aging proceeds, fertility problems arise, and the success rate of in vitro fertilization declines. During reproductive aging, rat ovaries present spontaneous formation of cysts, followed by a concomitant increase in sympathetic nerve activity, causing infertility and cessation of ovarian function. ß2-Adrenergic receptors, which are activated by noradrenaline (NA), modify follicular development and steroid secretions; thus, increased nerve activity has been associated with the development and maintenance of cystic structures. The purpose of this work was to block the effect of this sympathetic activity through in vivo administration of propranolol (a ß-adrenergic receptor antagonist) to determine whether it delays cyst formation and cessation of the ovarian function in rats that had reached the subfertile period. Propranolol was administrated daily to 8- and 10-month-old rats for 2 months. Estrous cycling activity was monitored by vaginal smear, serum concentration of the steroidal hormones was determined by enzyme-immune assay and morphological analysis of the ovaries was performed using 6 µm tissue slices stained with hematoxylin-eosin. Propranolol increased the number of healthy follicles, the ovulation rate, and levels of serum sexual steroids (androstenedione, testosterone, and estradiol) and recovered estrous cycling activity. It also decreased the number of follicular cysts. These results suggest that the blockade of ß-adrenergic receptors recovered ovarian function during reproductive aging. It is suggested that propranolol induces a time-dependent extension of the subfertile window, and it could be used to increase the success rate of fertility programs in aging woman.

The effects of acute and chronic nadolol treatment on ß2AR signaling in HEK293 cells.

Nadolol (NAD) is a ß-adrenergic receptor blocker with inverse agonist activity at ßARs. Previous studies in our laboratory showed that chronic treatment with NAD decreased airway resistance response (R (aw)) to the muscarinic agonist methacholine in a murine model of asthma while acute treatment with NAD increased R (aw) (Callaerts-Vegh et al., Proc Natl Acad Sci U S A 101:4948-4953, 2004). Chronic treatment with NAD also caused decreased airway inflammation and mucin content in a murine asthma model (Nguyen et al., Am J Respir Cell Mol Biol 38:256-262, 2008). In this study, we examined the effects of nadolol on ß(2)AR levels and signaling components downstream of the ß(2)AR using a line of HEK293 cells expressing human ß(2)ARs. Chronic treatment with NAD increased ß(2)AR protein levels and decreased receptor degradation, consistent with receptor stabilization by the inverse agonist. Basal cAMP levels decreased after 5 min of treatment with NAD but increased after a 24-h treatment. A 5-min treatment with NAD decreased forskolin-stimulated phosphorylation at the ß(2)AR PKA site Ser 262 while a 24-h treatment with NAD increased it. In contrast, chronic treatment with NAD had no effect on phosphorylation of the ß(2)AR GRK site at Ser 355, 356. Chronic treatment with NAD upregulated cellular levels of G(α)s but had no effect on G(α)i. Chronic NAD treatment therefore increases cellular cAMP levels by mechanisms that include the upregulation of ß(2)AR and G(α)s. This effect may explain in part the beneficial effects of chronic nadolol treatment on airway contractility.