Observational studies in humans and experimental studies in animals and isolated cells supported the widely held belief that hormone replacement therapy protects the cardiovascular system from disease. To nearly everyone’s astonishment, the Women’s Health Initiative Study and the Heart and Estrogen/Progestin Replacement Study overturned the conclusion that hormone replacement therapy protects the cardiovascular system and, in fact, supported the opposite view that such therapy may actually increase the risk of cardiovascular disease. This review addresses 2 questions: what went wrong and where do we go from here?

Oocyte in vitro maturation (IVM) and cryopreservation at the time of routine ovarian tissue freezing may be offered to cancer patients as an additional option for fertility preservation. This study aimed to investigate the developmental capacity of oocytes isolated from unstimulated ovaries.

Endothelial progenitor cells (EPCs) repair damaged endothelium and promote capillary formation, processes involving receptor tyrosine kinases (RTKs) and heme oxygenase 1 (HO-1). Because estradiol augments vascular repair, we hypothesize that estradiol increases EPC proliferation and capillary formation via RTK activation and induction of HO-1. Physiological concentrations of estradiol (10 nmol/L) increased EPC-induced capillary sprout and lumen formation in matrigel/fibrin/collagen systems. Propyl-pyrazole-triol (PPT; 100 nmol/L; estrogen receptor [ER]-α agonist), but not diarylpropionitrile (ER-β agonist), mimicked the stimulatory effects of estradiol on capillary formation, and methyl-piperidino-pyrazole (ER-α antagonist) abolished the effects of estradiol and PPT. Three different RTK activators (vascular endothelial growth factor, hepatocyte growth factor, and stromal derived growth factor 1) mimicked the capillary-stimulating effects of estradiol and PPT. SU5416 (RTK inhibitor) blocked the stimulatory effects of estradiol and PPT on capillary formation. Estradiol increased HO-1 expression by 2- to 3-fold, an effect blocked by SU5416, and PPT mimicked the effects of estradiol on HO-1. The ability of estradiol to enhance capillary formation, increase expression of HO-1, and augment phosphorylation of extracellular signal–regulated kinase 1/2, Akt, and vascular endothelial growth factor receptor 2 was mimicked by its cell-impermeable analog BSA estradiol. Actinomycin (transcription inhibitor) did not alter the effects of estradiol on RTK activity or vascular endothelial growth factor secretion. We conclude that estradiol via ER-α promotes EPC-mediated capillary formation by a mechanism that involves nongenomic activation of RTKs and HO-1 activation. Estradiol in particular and ER-α agonists in general may promote healing of injured vascular beds by promoting EPC activity leading to more rapid endothelial recovery and capillary formation after injury.

The goal of this study was to determine whether and how adenosine affects the proliferation of human coronary artery smooth muscle cells (HCASMCs). In HCASMCs, 2-chloroadenosine (stable adenosine analogue), but not N⁶-cyclopentyladenosine, CGS21680, or N⁶-(3-iodobenzyl)-adenosine-5′-N-methyluronamide, inhibited HCASMC proliferation (A_2Breceptor profile). 2-Chloroadenosine increased cAMP, reduced phosphorylation (activation) of ERK and Akt (protein kinases known to increase cyclin D expression and activity, respectively), and reduced levels of cyclin D1 (cyclin that promotes cell-cycle progression in G1). Moreover, 2-chloroadenosine inhibited expression of S-phase kinase–associated protein-2 (Skp2; promotes proteolysis of p27^Kip1) and upregulated levels of p27^Kip1(cell-cycle regulator that impairs cyclin D function). 2-Chloroadenosine also inhibited signaling downstream of cyclin D, including hyperphosphorylation of retinoblastoma protein and expression of cyclin A (S phase cyclin). Knockdown of A_2Breceptors prevented the effects of 2-chloroadenosine on ERK1/2, Akt, Skp2, p27^Kip1, cyclin D1, cyclin A, and proliferation. Likewise, inhibition of adenylyl cyclase and protein kinase A abrogated 2-chloroadenosine’s inhibitory effects on Skp2 and stimulatory effects on p27^Kip1and rescued HCASMCs from 2-chloroadenosine–mediated inhibition. Knockdown of p27^Kip1also reversed the inhibitory effects of 2-chloroadenosine on HCASMC proliferation. In vivo, peri-arterial (rat carotid artery) 2-chloroadenosine (20 μmol/L for 7 days) downregulated vascular expression of Skp2, upregulated vascular expression of p27^Kip1, and reduced neointima hyperplasia by 71% (P<0.05; neointimal thickness: control, 37 424±18 371 pixels; treated, 10 352±2824 pixels). In conclusion, the adenosine/A_2Breceptor/cAMP/protein kinase A axis inhibits HCASMC proliferation by blocking multiple signaling pathways (ERK1/2, Akt, and Skp2) that converge at cyclin D, a key G1 cyclin that controls cell-cycle progression.

The objectives of the present study were to determine whether adenosine attenuates proliferation of glomerular mesangial cells (GMCs), which adenosine receptor (AR) mediates the antimitogeneic actions of adenosine, and the cellular mechanisms by which adenosine inhibits growth of GMCs. Studies were conducted in both human and rat GMCs. Platelet-derived growth factor (PDGF)-BB (25 ng/mL) increased DNA synthesis ([³H]thymidine incorporation), cellular proliferation (cell number), collagen synthesis ([³H]proline incorporation), and mitogen-activated protein kinase (MAPK) activity, and these effects were attenuated by 2-chloroadenosine (nonselective AR agonist) and 5′-N-methylcarboxamidoadenosine (MECA; nonselective AR agonist), but not byN⁶-cyclopentyladenosine (selective A₁AR agonist), AB-N-MECA (selective A₃AR agonist), or CGS21680 (selective A_2AAR agonist). KF17837 (selective A_2A/BAR antagonist) and 1,3-dipropyl-8-p-sulfophenylxanthine (nonselective AR antagonist), but not 8-cyclopentyl-1,3-dipropylxanthine (selective A₁AR antagonist), blocked the growth-inhibitory effects of 2-chloroadenosine and 5′-N-MECA. Antisense, but not sense or scrambled, oligonucleotides to the A_2Breceptor increased both basal and PDGF-induced DNA synthesis, cell proliferation, and collagen synthesis, and the growth-inhibitory effects of 2-chloroadenosine, 5′-N-MECA, anderythro-9-(2-hydroxy-3-nonyl)adenine (inhibitor of adenosine deaminase) plus iodotubercidin (inhibitor of adenosine kinase) were abolished by antisense, but not scrambled or sense, oligonucleotides to the A_2Breceptor. We conclude that adenosine causes inhibition of GMC growth by activating A_2Breceptors coupled to inhibition of MAPK activity. A_2Breceptors may play an important role in regulating glomerular remodeling associated with GMC proliferation. Pharmacological or molecular biologic activation of A_2Breceptors may prevent glomerular remodeling associated with glomerulosclerosis, renal disease, and abnormal growth associated with hypertension and diabetes.