Cytosolic phospholipase A2 and eicosanoids modulate life, death and function of human osteoclasts in vitro

INTRODUCTION

Eicosanoids are important in bone physiology but the specific function of phopholipase enzymes has not been determined in osteoclasts. The objective of this is study was to determine the presence of cPLA2 in human in vitro-differentiated osteoclasts as well as osteoclasts in situ from bone biopsies.

MATERIALS AND METHODS

Osteoclastogenesis, apoptosis, bone resorption and the modulation of actin cytoskeleton assays were performed on osteoclasts differentiated in vitro. Immunohistochemistry was done in differentiated osteoclasts as well as on bone biopsies.

RESULTS

Human osteoclasts from normal, fetal, osteoarthritic, osteoporotic and Pagetic bone biopsies express cPLA2 and stimulation with RANKL increases cPLA2 phosphorylation in vitro. Inhibition of cPLA2 increased osteoclastogenesis and decreased apoptosis but decreased the capacity of osteoclasts to generate actin rings and to resorb bone.

DISCUSSION AND CONCLUSIONS

These results suggest that cPLA2 modulates osteoclast functions and could be a useful target in bone diseases with hyperactivated osteoclasts.

Prostaglandin D(2) induces apoptosis of human osteoclasts through ERK1/2 and Akt signaling pathways

In a recent study we have shown that prostaglandin D2 (PGD2) induces human osteoclast (OC) apoptosis through the activation of the chemoattractant receptor homologous molecule expressed on T-helper type 2 cell (CRTH2) receptor and the intrinsic apoptotic pathway. However, the molecular mechanisms underlying this response remain elusive. The objective of this study is to investigate the intracellular signaling pathways mediating PGD2-induced OC apoptosis. OCs were generated by in vitro differentiation of human peripheral blood mononuclear cells (PBMCs), and then treated with or without the selective inhibitors of mitogen-activated protein kinase-extracellular signal-regulated kinase (ERK) kinase, (MEK)-1/2, phosphatidylinositol3-kinase (PI3K) and NF-κB/IκB kinase-2 (IKK2) prior to the treatments of PGD2 as well as its agonists and antagonists. Fluorogenic substrate assay and immunoblotting were performed to determine the caspase-3 activity and key proteins involved in Akt, ERK1/2 and NF-κB signaling pathways. Treatments with both PGD2 and a CRTH2 agonist decreased ERK1/2 (Thr202/Tyr204) and Akt (Ser473) phosphorylation, whereas both treatments increased β-arrestin-1 phosphorylation (Ser412) in the presence of naproxen, which was used to eliminate endogenous prostaglandin production. In the absence of naproxen, treatment with a CRTH2 antagonist increased both ERK1/2 and Akt phosphorylations, and reduced the phosphorylation of β-arrestin-1. Treatment of OCs with a selective MEK-1/2 inhibitor increased caspase-3 activity and OC apoptosis induced by both PGD2 and a CRTH2 agonist. Moreover, a CRTH2 antagonist diminished the selective MEK-1/2 inhibitor-induced increase in caspase-3 activity in the presence of endogenous prostaglandins. In addition, treatment of OCs with a selective PI3K inhibitor decreased ERK1/2 (Thr202/Tyr204) phosphorylation caused by PGD2, whereas increased ERK1/2 (Thr202/Tyr204) phosphorylation by a CRTH2 antagonist was attenuated with a PI3K inhibitor treatment. The DP receptor was not implicated in any of the parameters evaluated. Treatment of OCs with PGD2 as well as its receptor agonists and antagonists did not alter the phosphorylation of RelA/p65 (Ser536). Moreover, the caspase-3 activity was not altered in OCs treated with a selective IKK2/NF-κB inhibitor. In conclusion, endogenous or exogenous PGD2 induces CRTH2-dependent apoptosis in human differentiated OCs; β-arrestin-1, ERK1/2, and Akt, but not IKK2/NF-κB are probably implicated in the signaling pathways of this receptor in the model studied.

Secreted phospholipase A2 type II is present in Paget's disease of bone and modulates osteoclastogenesis, apoptosis and bone resorption of human osteoclasts independently of its catalytic activity in vitro

OBJECTIVES

To study the role of secreted phospholipase A2 (sPLA2) in the pathophysiology of human osteoclasts (OCs).

METHODS

Immunohistochemistry and sPLA2 inhibitors were to determine the localization of sPLA2 and its role in OCs biology.

RESULTS

sPLA2 is expressed by OCs from healthy fetal bone and OCs from Paget's disease but not in normal bone. Inhibition of sPLA2 greatly reduces in vitro osteoclastogenesis.

DISCUSSION

The decrease in OCs formed could be attributed to a decline in the viability of CD14(+) OC precursors as well as a reduced viability of mature OCs. Inhibition of sPLA2 strongly decreases bone resorption by OCs independently of actin cytoskeleton remodeling, probably also by reducing OCs viability.

CONCLUSION

High amounts of this enzyme are present in fetal and Pagetic bone samples. Inhibition of sPLA2in vitro decreases osteoclastogenesis and OC activity and might constitute an interesting pharmacologic target for diseases with high bone turnover.

The proteasome inhibitor MG132 reduces immobilization-induced skeletal muscle atrophy in mice

Background

Skeletal muscle atrophy is a serious concern for the rehabilitation of patients afflicted by prolonged limb restriction. This debilitating condition is associated with a marked activation of NFκB activity. The ubiquitin-proteasome pathway degrades the NFκB inhibitor IκBα, enabling NFκB to translocate to the nucleus and bind to the target genes that promote muscle atrophy. Although several studies showed that proteasome inhibitors are efficient to reduce atrophy, no studies have demonstrated the ability of these inhibitors to preserve muscle function under catabolic condition.

Methods

We recently developed a new hindlimb immobilization procedure that induces significant skeletal muscle atrophy and used it to show that an inflammatory process characterized by the up-regulation of TNFα, a known activator of the canonical NFκB pathway, is associated with the atrophy. Here, we used this model to investigate the effect of in vivo proteasome inhibition on the muscle integrity by histological approach. TNFα, IL-1, IL-6, MuRF-1 and Atrogin/MAFbx mRNA level were determined by qPCR. Also, a functional measurement of locomotors activity was performed to determine if the treatment can shorten the rehabilitation period following immobilization.

Results

In the present study, we showed that the proteasome inhibitor MG132 significantly inhibited IκBα degradation thus preventing NFκB activation in vitro. MG132 preserved muscle and myofiber cross-sectional area by downregulating the muscle-specific ubiquitin ligases atrogin-1/MAFbx and MuRF-1 mRNA in vivo. This effect resulted in a diminished rehabilitation period.

Conclusion

These finding demonstrate that proteasome inhibitors show potential for the development of pharmacological therapies to prevent muscle atrophy and thus favor muscle rehabilitation.

BMP-9-induced muscle heterotopic ossification requires changes to the skeletal muscle microenvironment

Heterotopic ossification (HO) is defined as the formation of bone inside soft tissue. Symptoms include joint stiffness, swelling, and pain. Apart from the inherited form, the common traumatic form generally occurs at sites of injury in damaged muscles and is often associated with brain injury. We investigated bone morphogenetic protein 9 (BMP-9), which possesses a strong osteoinductive capacity, for its involvement in muscle HO physiopathology. We found that BMP-9 had an osteoinductive influence on mouse muscle resident stromal cells by increasing their alkaline phosphatase activity and bone-specific marker expression. Interestingly, BMP-9 induced HO only in damaged muscle, whereas BMP-2 promoted HO in skeletal muscle regardless of its state. The addition of the soluble form of the ALK1 protein (the BMP-9 receptor) significantly inhibited the osteoinductive potential of BMP-9 in cells and HO in damaged muscles. BMP-9 thus should be considered a candidate for involvement in HO physiopathology, with its activity depending on the skeletal muscle microenvironment.

A muscle resident cell population promotes fibrosis in hindlimb skeletal muscles of mdx mice through the Wnt canonical pathway

Previous work has pointed to a role for the Wnt canonical pathway in fibrosis formation in aged skeletal muscles. In the present study, we studied the dystrophic mdx mouse, which displays skeletal muscle fibrosis. Our results indicated that the muscle resident stromal cell (mrSC) population in the muscles of dystrophic mice is higher than in the muscles of age-matched wild-type mice. Wnt3a promoted the proliferation of and collagen expression by cultured mrSCs but arrested the growth of and collagen expression by cultured myoblasts. Injections of Wnt3A in the tibialis anterior muscles of adult wild-type mice significantly enhanced the mrSC population and collagen deposition compared with the contralateral muscles. Conversely, an injection of the Wnt antagonist Dickkof protein (DKK1) into the skeletal muscles of mdx mice significantly reduced collagen deposition. These results suggested that the Wnt canonical pathway expands the population of mrSCs and stimulates their production of collagen as observed during aging and in various myopathies.

Prediction of post-cardiopulmonary bypass cardiac output by venous oximetry

The present study evaluates two equations for predicting the post-cardiopulmonary bypass cardiac output (CO) in 10 patients undergoing coronary artery bypass grafting. One equation is based on the relationship of CO with mixed venous oxygen saturation (SVO 2), while the second equation is based on the relationship with oxygen extraction (1 - SVO 2). Each patient served as his own control. During bypass, when the patients were normothermic and perfused with a pump flow of 2.4 L/min/m 2, the SVO 2 was monitored by an in-line Bentley oxystat Meter. Just before termination of bypass, the pump flow was decreased to 0.4 L/min/m 2 and the left atrial pressure was increased to 10-15 mmHg; the resulting SVO 2 was recorded. The post-bypass CO was predicted in every patient by the two equations. Immediately after weaning from bypass, the cardiac output was measured by thermodilution. The thermodilutional CO measurement was correlated with the CO predicted by the two equations. Correlation analysis suggests that CO prediction is more accurate and approaches the 1:1 ratio when the calculation of predicted CO is based on the relationship between cardiac output and oxygen extraction.

The hemodynamic effects of intravenous norepinephrine versus epinephrine and phenylephrine in patients with ischemic heart disease

The hemodynamic effects of an intravenous bolus of norepinephrine 10 micrograms, phenylephrine 100 micrograms and epinephrine 10 micrograms were investigated in 30 patients scheduled for coronary artery bypass grafting. The hemodynamic changes following norepinephrine were similar to those achieved by phenylephrine. Both drugs increased the mean blood pressure and systemic vascular resistance without any significant change of cardiac output. In contrast, epinephrine increased the mean arterial pressure and cardiac output without a significant change of systemic vascular resistance. The results suggest that intravenous norepinephrine acts similar to phenylephrine as an alpha-adrenergic agonist, while epinephrine acts predominantly as a beta-adrenergic agonist.

Continuous venous oximetry during cardiopulmonary bypass: influence of temperature changes, perfusion flow, and hematocrit levels

This study was performed in 11 patients undergoing cardiac surgery during cardiopulmonary bypass (CPB). A Bentley-10 oxygenator (American Bentley, Irvine, CA) was used during bypass, and 1,500 mL of Ringer's solution was used to prime the oxygenator. A perfusion flow of 2.4 L/min/m2 was used, and an equivalent flow of 100% oxygen was added to the oxygenator. The mixed venous oxygen saturation (SvO2) was monitored by continuous in-line venous oximetry using the Bentley Oxy-Stat Meter. Body temperature and SvO2 measurements were made at the venous blood port of the oxygenator. The authors investigated the correlation between SvO2 and changes of body temperature, perfusion flow, and hematocrit values. SvO2 correlated inversely, in a linear fashion, with the body temperature. The SvO2 was markedly decreased after rewarming, and was significantly affected during normothermia by changes in perfusion flow rates and hematocrit levels. An adequate SvO2 was found when the flow was greater than 2.4 L/min/m2 and the hematocrit was greater than 20%. In-line oximetry can help to optimize perfusion during CPB and to detect episodes of desaturation.

Action of adrenergic agonists on resistance v capacitance vessels during cardiopulmonary bypass

The peripheral vascular effects of three different adrenergic agonists were investigated in 13 patients undergoing valve replacement during cardiopulmonary bypass (CPB). The venous reservoir (RV) and mean arterial pressure (MAP) were used as indices of the changes in venous capacitance and arterial resistance, respectively, produced by the adrenergic agonists. Isoproterenol, a pure beta-adrenergic agonist, decreased both MAP and RV. Norepinephrine (NE), which activates both alpha 1- and alpha 2-receptors in humans, increased both MAP and RV, while phenylephrine (PH) a selective alpha 1-adrenergic agonist, increased only MAP with no significant change in RV. It is concluded that in humans during hypothermic CPB, beta-agonists dilate both the resistance and capacitance vessels, selective alpha 1-adrenergic agonists preferentially constrict the resistance vessels, and non-selective alpha 1- and alpha 2-adrenergic agonists constrict both the resistance and capacitance vessels.

Effects of preoperative calcium channel and beta-adrenergic blockade on the vascular response to adrenergic agonists during cardiopulmonary bypass

The present report compares the effects of isoproterenol (ISO), norepinephrine (NE), and phenylephrine (PH) on the mean arterial pressure (MAP) and reservoir volume (RV) during cardiopulmonary (CPB) in 16 patients undergoing coronary artery bypass grafting (CABG) who were treated preoperatively with oral nifedipine (10 to 40 mg, three times a day) and propranolol (40 to 60 mg, three times a day). The changes of RV and MAP were used as indices of the changes in venous capacitance and arterial resistance, respectively, produced by the adrenergic agonists. ISO, a beta-adrenergic agonist, decreased both MAP and RV. NE, which activates both alpha 1- and alpha 2- adrenoceptors, increased both MAP and RV, while PH, a selective alpha 1-adrenergic agonist, increased only MAP with no significant change in RV. The changes are qualitatively similar to those previously achieved in patients undergoing valve replacement who did not receive any blocker preoperatively. However, the decrease of MAP by ISO and its increase by NE were significantly less in the CABG group. It is concluded that preoperative preparation of patients undergoing CABG with beta-adrenergic blockers and calcium channel blockers can modify the effect of ISO and NE on the peripheral resistance, but they have no significant effect on the action of PH at the doses selected in this study.

Verapamil pretreatment before aortic cross-clamping in patients undergoing coronary artery bypass graft

In 12 of 22 patients with coronary artery disease undergoing elective coronary artery bypass graft (CABG), verapamil (0.075 mg/kg body weight) pretreatment was given on initiation of cardiopulmonary bypass (CPB) before aortic cross-clamping (ACC), whereas no verapamil was used in 10 control patients. The volume of cardioplegia solution required to achieve and maintain cardiac asystole during ACC while on CPB was not significantly different in the two groups. After the release of ACC, the energy of direct current countershock required for defibrillation, the incidence of heart block, and the need for pacemaker were not significantly different. However, defibrillation was more readily achieved by a single countershock in the verapamil group than in the control group. Also, the incidence of ST segment changes after defibrillation was significantly lower in the verapamil group, suggesting that verapamil pretreatment before ACC may potentiate the myocardial preservation achieved by the cardioplegia, and hence may decrease the incidence of ischemic changes during the critical reperfusion period.

Hemodynamic effects of diazepam-vecuronium-fentanyl sequence for induction of anesthesia for coronary artery surgery

The hemodynamic effects of diazepam (0.2 mg/kg)--vecuronium (0.2 mg/kg)--fentanyl (10 micrograms/kg) sequence was investigated when used for induction of anesthesia and tracheal intubation in eleven patients undergoing CABG. The parameters monitored included HR, SBP, PAP and PCWP. Also, EKG was monitored via a modified V5 lead and C.O was measured by thermodilution. SVR, PVR and SV were computed from the measured parameters. Following induction of anesthesia by diazepam-vecuronium-fentanyl sequence, there was a decrease in SBP by 20.0% (P less than 0.05), in HR by 15.7% (P less than 0.001) in C.O by 13.3% (P less than 0.01) and in SVR by 13.6% (P less than 0.05) of control value. There were no changes in PAP, PCWP, PVR and SV. Coronary perfusion pressure and heart rate product were both decreased following this induction sequence. However, the percentage decrease in PR was higher than that of CPP, affecting favorably the myocardial oxygen supply-demand balance. Orotracheal intubation was followed by an increase of HR by 10.7% (P less than 0.05), SVR by 13% (P less than 0.05) and PCWP by 26% (P less than 0.05) of preceding value. However, all these values did not reach the control awake values. It was concluded that diazepam (0.2 mg/kg)--vecuronium (0.2 mg/kg)--fentanyl (10 micrograms/kg) sequence does not produce serious hemodynamic changes when used for induction of anesthesia and tracheal intubation in patients undergoing coronary artery bypass surgery.