Title: β3 Adrenergic Receptor Signaling in the Human Myometrium

Nicotine regulates abnormal macrophage polarization and trophoblast invasion associated with preterm labor via the α7nAChR/SIRT1 axis

INTRODUCTION

Preterm birth (PTB) frequently results from the syndrome of preterm labor (PTL). PTL is linked to an atypical maternal inflammatory response, as well as intrauterine inflammation and/or infection. In this study, we explored the mechanisms involved in nicotine-mediated abnormal macrophage polarization and trophoblast invasion associated with PTL.

METHODS

First, THP-1-M0 macrophages were generated by treating the human monocytic leukemia cell line (THP-1) with phorbol 12-myristate 13-acetate for a duration of 24 h. Afterward, nicotine treatment was administered, followed by coculturing with the HTR-8/SVneo trophoblast cell line (HTR-8) at a ratio of 1:1. Next, we transfected sh-α7nAChR and treated THP-1-M0 macrophages and HTR-8 cells with nicotine. In addition, we transfected THP-1-M0 macrophages with sh-NC or sh-SIRT1 or subjected them to 4 nM nicotinamide adenine dinucleotide (NAD) metabolic inhibitor FK866 treatment. Moreover, HTR-8 cells were treated with nicotine, after which THP-1-M0 macrophages were cocultured with HTR-8 cells. Finally, we constructed an in vivo RU486-induced PTL rat model to verify the effect of nicotine and the mechanisms involved.

RESULTS

We found that nicotine affected polarization and α7nAChR expression in HTR-8 cocultured THP-1-M0 macrophages. Knocking down α7nAChR blocked the effect of nicotine on the proliferation and invasion of HTR-8 cells. Furthermore, nicotine activated the α7nAChR/SIRT1 axis to regulate THP-1-M0 macrophage polarization through the cholinergic anti-inflammatory pathway. Additionally, NAD metabolism mediated the role of the α7nAChR/SIRT1 axis in nicotine-induced polarization of HTR-8 cocultured THP-1-M0 macrophages. In vivo experiments demonstrated that nicotine alleviated inflammation in PTL rats, which involved the α7nAChR/SIRT1 axis.

CONCLUSION

Nicotine regulated abnormal macrophage polarization and trophoblast invasion associated with PTL via the α7nAChR/SIRT1 axis.

Inside the Biology of the β3-Adrenoceptor

Since the first discovery in 1989, the β3-adrenoceptor (β3-AR) has gained great attention because it showed the ability to regulate many physiologic and metabolic activities, such as thermogenesis and lipolysis in brown and white adipose tissue, respectively (BAT, WAT), negative inotropic effects in cardiomyocytes, and relaxation of the blood vessels and the urinary bladder. The β3-AR has been suggested as a potential target for cancer treatment, both in adult and pediatric tumors, since under hypoxia its upregulation in the tumor microenvironment (TME) regulates stromal cell differentiation, tumor growth and metastases, signifying that its agonism/antagonism could be useful for clinical benefits. Promising results in cancer research have proposed the β3-AR being targeted for the treatment of many conditions, with some drugs, at present, undergoing phase II and III clinical trials. In this review, we report the scientific journey followed by the research from the β3-Ars' discovery, with focus on the β3-Ars' role in cancer initiation and progression that elects it an intriguing target for novel antineoplastic approaches. The overview highlights the great potential of the β3-AR, both in physiologic and pathologic conditions, with the intention to display the possible benefits of β3-AR modulation in cancer reality.

β3 Receptor Signaling in Pregnant Human Myometrium Suggests a Role for β3 Agonists as Tocolytics

Preterm labor leading to preterm birth is the leading cause of infant morbidity and mortality. At the present time, nothing can reliably halt labor once it begins. The knowledge that agonists of the β2 adrenergic receptor relax airway smooth muscle and are effective in the treatment of asthma led to the notion that β2 mimetics would prevent preterm birth by relaxing uterine smooth muscle. The activation of cAMP-dependent protein kinase by β2 receptors is unable to provide meaningful tocolysis. The failure of β2 agonists such as ritodrine and terbutaline to prevent preterm birth suggests that the regulation of uterine smooth muscle is disparate from that of airway. Other smooth muscle quiescent-mediating molecules, such as nitric oxide, relax vascular smooth muscle in a cGMP-protein kinase G-dependent manner; however, nitric oxide activation of protein kinase G fails to explain the relaxation of the myometrium to nitric oxide. Moreover, nitric oxide-mediated relaxation is blunted in preterm labor, and thus, for this reason and because of the fall in maternal blood pressure, nitric oxide cannot be employed as a tocolytic. The β3 adrenergic receptor-mediated relaxation of the human myometrium is claimed to be cAMP-dependent protein kinase-dependent. This is scientifically displeasing given the failure of β2 agonists as tocolytics and suggests a non-canonical signaling role for β3AR in myometrium. The addition of the β3 agonist mirabegron to pregnant human myometrial strips in the tissue bath relaxes oxytocin-induced contractions. Mirabegron stimulates nitric oxide production in myometrial microvascular endothelial cells, and the relaxation of uterine tissue in vitro is partially blocked by the addition of the endothelial nitric oxide synthase blocker Nω-Nitro-L-arginine. Recent data suggest that both endothelial and smooth muscle cells respond to β3 stimulation and contribute to relaxation through disparate signaling pathways. The repurposing of approved medications such as mirabegron (Mybetriq™) tested in human myometrium as uterine tocolytics can advance the prevention of preterm birth.

Novel identification and modulation of the mechanosensitive Piezo1 channel in human myometrium

Approximately 10% of US births deliver preterm before 37 weeks of completed gestation. Premature infants are at risk for life-long debilitating morbidities and death, and spontaneous preterm labour explains 50% of preterm births. In all cases existing treatments are ineffective, and none are FDA approved. The mechanisms that initiate preterm labour are not well understood but may result from dysfunctional regulation of quiescence mechanisms. Human pregnancy is accompanied by large increases in blood flow, and the uterus must enlarge by orders of magnitude to accommodate the growing fetus. This mechanical strain suggests that stretch-activated channels may constitute a mechanism to explain gestational quiescence. Here we identify for the first time that Piezo1, a mechanosensitive cation channel, is present in the uterine smooth muscle and microvascular endothelium of pregnant myometrium. Piezo is downregulated during preterm labour, and stimulation of myometrial Piezo1 in an organ bath with the agonist Yoda1 relaxes the tissue in a dose-dependent fashion. Further, stimulation of Piezo1 while inhibiting protein kinase A, AKT, or endothelial nitric oxide synthase mutes the negative inotropic effects of Piezo1 activation, intimating that actions on the myocyte and endothelial nitric oxide signalling contribute to Piezo1-mediated contractile dynamics. Taken together, these data highlight the importance of stretch-activated channels in pregnancy maintenance and parturition, and identify Piezo1 as a tocolytic target of interest. KEY POINTS: Spontaneous preterm labour is a serious obstetric dilemma without a known cause or effective treatments. Piezo1 is a stretch-activated channel important to muscle contractile dynamics. Piezo1 is present in the myometrium and is dysregulated in women who experience preterm labour. Activation of Piezo1 by the agonist Yoda1 relaxes the myometrium in a dose-dependent fashion, indicating that Piezo1 modulation may have therapeutic benefits to treat preterm labour.