Role of Phosphatidylinositol 3-Kinase (PI3K), Mitogen-Activated Protein Kinase (MAPK), and Protein Kinase C (PKC) in Calcium Signaling Pathways Linked to the α1-Adrenoceptor in Resistance Arteries

Insulin resistance plays a key role in the pathogenesis of type 2 diabetes and is also related to other health problems like obesity, hypertension, and metabolic syndrome. Imbalance between insulin vascular actions via the phosphatidylinositol 3-Kinase (PI3K) and the mitogen activated protein kinase (MAPK) signaling pathways during insulin resistant states results in impaired endothelial PI3K/eNOS- and augmented MAPK/endothelin 1 pathways leading to endothelial dysfunction and abnormal vasoconstriction. The role of PI3K, MAPK, and protein kinase C (PKC) in Ca²⁺ handling of resistance arteries involved in blood pressure regulation is poorly understood. Therefore, we assessed here whether PI3K, MAPK, and PKC play a role in the Ca²⁺ signaling pathways linked to adrenergic vasoconstriction in resistance arteries. Simultaneous measurements of intracellular calcium concentration ([Ca²⁺]_i) in vascular smooth muscle (VSM) and tension were performed in endothelium-denuded branches of mesenteric arteries from Wistar rats mounted in a microvascular myographs. Responses to CaCl₂ were assessed in arteries activated with phenylephrine (PE) and kept in Ca²⁺-free solution, in the absence and presence of the selective antagonist of L-type Ca²⁺ channels nifedipine, cyclopiazonic acid (CPA) to block sarcoplasmic reticulum (SR) intracellular Ca²⁺ release or specific inhibitors of PI3K, ERK-MAPK, or PKC. Activation of α₁-adrenoceptors with PE stimulated both intracellular Ca²⁺ mobilization and Ca²⁺ entry along with contraction in resistance arteries. Both [Ca²⁺]_i and contractile responses were inhibited by nifedipine while CPA abolished intracellular Ca²⁺ mobilization and modestly reduced Ca²⁺ entry suggesting that α₁-adrenergic vasoconstriction is largely dependent Ca²⁺ influx through L-type Ca²⁺ channel and to a lesser extent through store-operated Ca²⁺ channels. Inhibition of ERK-MAPK did not alter intracellular Ca²⁺ mobilization but largely reduced L-type Ca²⁺ entry elicited by PE without altering vasoconstriction. The PI3K blocker LY-294002 moderately reduced intracellular Ca²⁺ release, Ca²⁺ entry and contraction induced by the α₁-adrenoceptor agonist, while PKC inhibition decreased PE-elicited Ca²⁺ entry and to a lesser extent contraction without affecting intracellular Ca²⁺ mobilization. Under conditions of ryanodine receptor (RyR) blockade to inhibit Ca²⁺-induced Ca²⁺-release (CICR), inhibitors of PI3K, ERK-MAPK, or PKC significantly reduced [Ca²⁺]_i increases but not contraction elicited by high K⁺ depolarization suggesting an activation of L-type Ca²⁺ entry in VSM independent of RyR. In summary, our results demonstrate that PI3K, ERK-MAPK, and PKC regulate Ca²⁺ handling coupled to the α₁-adrenoceptor in VSM of resistance arteries and related to both contractile and non-contractile functions. These kinases represent potential pharmacological targets in pathologies associated to vascular dysfunction and abnormal Ca²⁺ handling such as obesity, hypertension and diabetes mellitus, in which these signaling pathways are profoundly impaired.

Peucedanum japonicum Thunb. ethanol extract suppresses RANKL-mediated osteoclastogenesis

The constituents of Peucedanum japonicum Thunb. (PJ) exhibit biological and pharmacological activities, including anti-obesity, anti-oxidant and anti-allergic activities. The aim of the present study was to examine in vitro effects of PJ in RANKL-induced signaling pathways, which determine osteoclast differentiation. PJ ethanol extract (PEE) exhibited anti-osteoporotic activity by disrupting the phospholipase C (PLC)-Ca2+-c-Fos/cAMP response element-binding protein (CREB)-nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) signaling pathway during osteoclastogenesis. Murine bone marrow-derived macrophages (BMMs) were cultured and used to determine the effects of PJ in the receptor activator of nuclear factor κB ligand (RANKL)-mediated osteoclastogenesis. The effects of PEE in the RANKL-mediated signaling cascade were evaluated using a standard in vitro osteoclastogenesis system. PEE treatment of BMMs significantly reduced the number of RANKL-mediated tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells (P<0.05 for 5 and 10 µg/ml PEE, P<0.01 for 25 and 50 µg/ml PEE), without cytotoxic effects. Furthermore, the expression of differentiation-related marker genes, including TRAP, Oscar, Cathepsin K, dendrocyte expressed seven transmembrane protein, ATPase H+ Transporting V0 Subunit D2 and NFATc1, were markedly suppressed. PEE induced a transient increase in free cytoplasmic Ca2+ ([Ca2+]_i) mobilization via voltage-gated Ca2+ channels and PLC-sensitive pathways. Transient [Ca2+]_i increase consequently resulted in the suppression of c-Fos, CREB and NFATc1 activities. These findings highlight the potential use of PJ in treating bone disorders caused by osteoclast overgrowth.