Inhibitory mechanisms of docosahexaenoic acid on carbachol-, angiotensin II-, and bradykinin-induced contractions in guinea pig gastric fundus smooth muscle

We studied the inhibitory actions of docosahexaenoic acid (DHA) on the contractions induced by carbachol (CCh), angiotensin II (Ang II), and bradykinin (BK) in guinea pig (GP) gastric fundus smooth muscle (GFSM), particularly focusing on the possible inhibition of store-operated Ca2+ channels (SOCCs). DHA significantly suppressed the contractions induced by CCh, Ang II, and BK; the inhibition of BK-induced contractions was the strongest. Although all contractions were greatly dependent on external Ca2+, more than 80% of BK-induced contractions remained even in the presence of verapamil, a voltage-dependent Ca2+ channel inhibitor. BK-induced contractions in the presence of verapamil were not suppressed by LOE-908 (a receptor-operated Ca2+ channel (ROCC) inhibitor) but were suppressed by SKF-96365 (an SOCC and ROCC inhibitor). BK-induced contractions in the presence of verapamil plus LOE-908 were strongly inhibited by DHA. Furthermore, DHA inhibited GFSM contractions induced by cyclopiazonic acid (CPA) in the presence of verapamil plus LOE-908 and inhibited the intracellular Ca2+ increase due to Ca2+ addition in CPA-treated 293T cells. These findings indicate that Ca2+ influx through SOCCs plays a crucial role in BK-induced contraction in GP GFSM and that this inhibition by DHA is a new mechanism by which this fatty acid inhibits GFSM contractions.

Chronic hypoxia promoted pulmonary arterial smooth muscle cells proliferation through upregulated calcium-sensing receptorcanonical transient receptor potential 1/6 pathway

OBJECTIVES

Although both calcium-sensing receptor (CaSR) and canonical transient receptor potential (TRPC) proteins contribute to chronic hypoxia (CH)-induced pulmonary arterial smooth muscle cells (PASMCs) proliferation, the relationship between CaSR and TRPC in hypoxic PASMCs proliferation remains poorly understood. The goal of this study was to identify that CH promotes PASMCs proliferation through CaSR-TRPC pathway.

METHODS

Rat PASMCs were isolated and treated with CH. Cell proliferation was assessed by cell counting, CCK-8 assay, and EdU incorporation. CaSR and TRPC expressions were determined by qPCR and Western blotting. Store-operated Ca²⁺ entry (SOCE) was assessed by extracellular Ca²⁺ restoration.

RESULTS

In PASMCs, CH enhanced the cell number, cell viability and DNA synthesis, which is accompanied by upregulated expression of CaSR, TRPC1 and TRPC6. Negative CaSR modulators (NPS2143, NPS2390) inhibited, whereas positive modulators (spermine, R568) enhanced, the CH-induced increases in cell number, cell viability and DNA synthesis in PASMCs. Knockdown of CaSR by siRNA inhibited the CH-induced upregulation of TRPC1 and TRPC6 and enhancement of SOCE and attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs. However, neither siTRPC1 nor siTRPC6 had an effect on the CH-induced CaSR upregulation, although both significantly attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs.

CONCLUSION

These results demonstrate that upregulated CaSR-TRPC1/6 pathway mediating PASMCs proliferation is an important pathogenic mechanism under hypoxic conditions.

Platelet-derived growth factor-BB induces pulmonary venous smooth muscle cells proliferation by upregulating calcium sensing receptor under hypoxic conditions

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling, which exists in both pulmonary arteries and pulmonary veins. Pulmonary vascular remodeling stems from excessive proliferation of pulmonary vascular myocytes. Platelet-derived growth factor-BB (PDGF-BB) is a vital vascular regulator whose level increases in PH human lungs. Although the mechanisms by which pulmonary arterial smooth muscle cells respond to PDGF-BB have been studied extensively, the effects of PDGF-BB on pulmonary venous smooth muscle cells (PVSMCs) remain unknown. We herein examined the involvement of calcium sensing receptor (CaSR) in PDGF-BB-induced PVSMCs proliferation under hypoxic conditions. In PVSMCs isolated from rat intrapulmonary veins, PDGF-BB increased the cell number and DNA synthesis under normoxic and hypoxic conditions, which was accompanied by upregulated CaSR expression. The influences of PDGF-BB on proliferation and CaSR expression in hypoxic PVSMCs were greater than that in normoxic PVSMCs. In hypoxic PVSMCs superfused with Ca²⁺-free solution, restoration of extracellular Ca²⁺ induced an increase of [Ca²⁺]_i, which was significantly smaller than that in PDGF-BB-treated hypoxic PVSMCs. The positive CaSR modulator spermine enhanced, whereas the negative CaSR modulator NPS2143 attenuated, the extracellular Ca²⁺-induced [Ca²⁺]_i increase in PDGF-BB-treated hypoxic PVSMCs. Furthermore, the spermine enhanced, whereas the NPS2143 inhibited, PDGF-BB-induced proliferation in hypoxic PVSMCs. Silencing CaSR with siRNA attenuated the extracellular Ca²⁺-induced [Ca²⁺]_i increase in PDGF-BB-treated hypoxic PVSMCs and inhibited PDGF-BB-induced proliferation in hypoxic PVSMCs. In conclusion, these results demonstrated that CaSR mediating PDGF-BB-induced excessive PVSMCs proliferation is an important mechanism involved in the initiation and progression of PVSMCs proliferation under hypoxic conditions.

Long Noncoding RNA COPDA1 Promotes Airway Smooth Muscle Cell Proliferation in Chronic Obstructive Pulmonary Disease

Abnormal expression of long noncoding RNAs (lncRNAs) has been confirmed to be associated with many diseases, including chronic obstructive pulmonary disease (COPD). To gain better understanding of the mechanism of COPD, we investigated the lncRNA and mRNA profiles in the lung tissue of patients with COPD. According to the analysis, one of the significantly different lncRNAs, COPDA1, might participate in the occurrence and development of COPD. Lung tissues were collected from nonsmokers, smokers, or smokers with COPD for RNA sequencing. Bioinformatic analysis and cell experiments were used to define the function of COPDA1, and the effects of COPDA1 on intracellular Ca²⁺ concentration and cell proliferation were examined after knockdown or overexpression of COPDA1. A number of variations of lncRNAs were found in the comparison of nonsmokers, smokers, and smokers with COPD. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analyses indicated that smoking was involved in the activation of cytokines and the cell cycle, which is associated with COPD. According to the lncRNA-mRNA-coexpressing network and enrichment analysis, COPDAz1 and one of its target genes, MS4A1 (membrane-spanning 4-domains family, subfamily A) were investigated, and we discovered that the expression of MS4A1 was closely associated with lncRNA COPDA1 expression in human bronchial smooth muscle cells (HBSMCs). Further study showed that lncRNA COPDA1 upregulated the expression of MS4A1 to increase store-operated calcium entry in the HBSMCs, resulting in the promotion of the proliferation of smooth muscle cells as well as of airway remodeling. COPDA1 might be involved in the regulation of certain signaling pathways in COPD, might promote the proliferation of HBSMCs, and might also be involved in facilitating airway remodeling.

Role of TG2-Mediated SERCA2 Serotonylation on Hypoxic Pulmonary Vein Remodeling

Sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) pumps take up Ca2+ from the cytoplasm to maintain the balance of intracellular Ca2+. A decline in expression or activity of SERCA results in persistent store-operated calcium entry (SOCE). In cardiomyocytes as well as vascular smooth muscle cells (SMCs), SERCA2 acts as an important regulator of calcium cycling. The purpose of this study is to identify and better understand the role of transglutaminases2 (TG2) as a key factor involved in SERCA2 serotonination (s-SERCA2) and to elucidate the underlying mechanism of action. Human pulmonary venous smooth muscle cell in normal pulmonary lobe were isolated and cultured in vitro. Establishment of hypoxic pulmonary hypertension model in wild type and TG2 knockout mice. SERCA2 serotonylation was analyzed by co-(immunoprecipitation) IP when the TG2 gene silenced or overexpressed under normoxia and hypoxia in vivo and in vitro. Intracellular calcium ion was measured by using Fluo-4AM probe under normoxia and hypoxia. Real-time (RT)-PCR and Western blot analyzed expression of TG2, TRPC1, and TRPC6 under normoxia and hypoxia. Bioactivity of cells were analyzed by using Cell Counting Kit (CCK)-8, flow cytometry, wound healing, RT-PCR, and Western blot under PST-2744 and cyclopiazonic acid. We confirmed that 1) hypoxia enhanced the expression and activity of TG2, and 2) hypoxia increased the basal intracellular Ca2+ concentration ([Ca2+]i) and SOCE through activating TRPC6 on human pulmonary vein smooth muscle cells (hPVSMC). Then, we investigated the effects of overexpression and downregulation of the TG2 gene on the activity of SERCA2, s-SERCA2, basal [Ca2+]i, and SOCE under normoxia and hypoxia in vitro, and investigated the activity of SERCA2 and s-SERCA2 in vivo, respectively. We confirmed that SERCA2 serotonylation inhibited the activity of SERCA2 and increased the Ca2+ influx, and that hypoxia induced TG2-mediated SERCA2 serotonylation both in vivo and in vitro. Furthermore, we investigated the effect of TG2 activity on the biological behavior of hPVSMC by using an inhibitor and agonist of SERCA2, respectively. Finally, we confirmed that chronic hypoxia cannot increase vessel wall thickness, the right ventricular systolic pressure (RVSP), and right ventricular hypertrophy index (RVHI) of vascular smooth muscle-specific Tgm2−/− mice. These results indicated that hypoxia promoted TG2-mediated SERCA2 serotonylation, thereby leading to inhibition of SERCA2 activity, which further increased the calcium influx through the TRPC6 channel. Furthermore, tissue-specific conditional TG2 knockout mice prevents the development of pulmonary hypertension caused by hypoxia. In summary, we uncovered a new target (TG2) for treatment of chronic hypoxic pulmonary hypertension (CHPH).

A novel function of calcium sensing receptor in chronic hypoxia-induced pulmonary venous smooth muscle cells proliferation

Chronic hypoxia (CH) causes remodeling not only in pulmonary arteries but also in pulmonary veins. Pulmonary vascular remodeling stems from increased pulmonary vascular myocyte proliferation. However, the pathogenesis of CH-induced proliferation of pulmonary venous smooth muscle cells (PVSMCs) remains unknown. The present study aimed to explore the mechanisms by which CH affects PVSMCs proliferation. PVSMCs were isolated from rat distal pulmonary veins and exposed to CH (4% O₂ for 60 h). The expression of calcium sensing receptor (CaSR) was determined by immunofluorescence, real-time quantitative PCR and Western blotting. Cell proliferation was assessed by cell counting, CCK-8 assay, and BrdU incorporation. Apoptosis analysis was examined by flow cytometry. In rat distal PVSMCs, CH increased the cell number and cell viability and enhanced DNA synthesis, which is accompanied by upregulated mRNA and protein expression levels of CaSR. Two negative CaSR modulators (NPS2143, NPS2390) not only attenuated CH-induced CaSR upregulation but also inhibited CH-induced increases in cell number, cell viability and the proliferation index of PVSMCs, whereas two positive modulators (spermine, R568) not only amplified CH-induced CaSR upregulation but also intensified CH-induced increases in cell number, cell viability and the proliferation index of PVSMCs. Silencing CaSR with siRNA similarly attenuated the CH-induced enhancement of cell number, cell viability and DNA synthesis in PVSMCs. Neither CH nor downregulation of CaSR with siRNA had an effect on apoptosis in PVSMCs. These results suggest that CaSR mediating excessive proliferation is a new pathogenic mechanism involved in the initiation and progression of distal PVSMCs proliferation under CH conditions.

Hypoxia selectively upregulates cation channels and increases cytosolic [Ca2+] in pulmonary, but not coronary, arterial smooth muscle cells

Ca²⁺ signaling, particularly the mechanism via store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca²⁺] ([Ca²⁺]_cyt) and the stored [Ca²⁺] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca²⁺ oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na⁺/Ca²⁺ exchanger-mediated increases in [Ca²⁺]_cyt did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O₂ for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca²⁺]_cyt only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca²⁺ channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

Chloroquine is a potent pulmonary vasodilator that attenuates hypoxia-induced pulmonary hypertension

BACKGROUND AND PURPOSE

Sustained pulmonary vasoconstriction and excessive pulmonary vascular remodelling are two major causes of elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension. The purpose of this study was to investigate whether chloroquine induced relaxation in the pulmonary artery (PA) and attenuates hypoxia-induced pulmonary hypertension (HPH).

EXPERIMENTAL APPROACH

Isometric tension was measured in rat PA rings pre-constricted with phenylephrine or high K⁺ solution. PA pressure was measured in mouse isolated, perfused and ventilated lungs. Fura-2 fluorescence microscopy was used to measure cytosolic free Ca²⁺ concentration levels in PA smooth muscle cells (PASMCs). Patch-clamp experiments were performed to assess the activity of voltage-dependent Ca²⁺ channels (VDCCs) in PASMC. Rats exposed to hypoxia (10% O₂ ) for 3 weeks were used as the model of HPH or Sugen5416/hypoxia (SuHx) for in vivo experiments.

KEY RESULTS

Chloroquine attenuated agonist-induced and high K⁺ -induced contraction in isolated rat PA. Pretreatment with l-NAME or indomethacin and functional removal of endothelium failed to inhibit chloroquine-induced PA relaxation. In PASMC, extracellular application of chloroquine attenuated store-operated Ca²⁺ entry and ATP-induced Ca²⁺ entry. Furthermore, chloroquine also inhibited whole-cell Ba²⁺ currents through VDCC in PASMC. In vivo experiments demonstrated that chloroquine treatment ameliorated the HPH and SuHx models.

CONCLUSIONS AND IMPLICATIONS

Chloroquine is a potent pulmonary vasodilator that may directly or indirectly block VDCC, store-operated Ca²⁺ channels and receptor-operated Ca²⁺ channels in PASMC. The therapeutic potential of chloroquine in pulmonary hypertension is probably due to the combination of its vasodilator, anti-proliferative and anti-autophagic effects.

Isolation, culture and identification of pulmonary arterial smooth muscle cells from rat distal pulmonary arteries

The culture of pulmonary arterial smooth muscle cells (PASMCs) is one of the most powerful tools for exploring the mechanisms of pulmonary hypertension (PH). Both pulmonary vasoconstriction and remodeling occur predominantly in distal pulmonary arteries (PA). In this study, we provide our detailed and standardized protocol for easy isolation and culture of PASMCs from rat distal PA to supply every investigator with a simple, economical and useful method in studying PH. The protocol can be divided into four stages: isolation of distal PA, isolation of cells, growth in culture and passage of cells. Rat distal PASMCs were characterized by morphological activity and by immunostaining for smooth muscle α-actin and smooth muscle myosin heavy chain, but not for CD90/Thy-1 or von Willebrand factor. Furthermore, functional assessments were performed, confirming the presence of voltage-dependent Ca²⁺ channels and physiological characteristic of response to hypoxia. In conclusion, we have developed a detailed and simple protocol for obtaining rat distal PASMCs. These PASMCs exhibit features consistent with vascular smooth muscle cells, and they could subsequently be used to further explore the pathophysiological mechanisms of PH.

Molecular Mechanisms of Pulmonary Vascular Remodeling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease that is precipitated by hypertrophic pulmonary vascular remodeling of distal arterioles to increase pulmonary artery pressure and pulmonary vascular resistance in the absence of left heart, lung parenchymal, or thromboembolic disease. Despite available medical therapy, pulmonary artery remodeling and its attendant hemodynamic consequences result in right ventricular dysfunction, failure, and early death. To limit morbidity and mortality, attention has focused on identifying the cellular and molecular mechanisms underlying aberrant pulmonary artery remodeling to identify pathways for intervention. While there is a well-recognized heritable genetic component to PAH, there is also evidence of other genetic perturbations, including pulmonary vascular cell DNA damage, activation of the DNA damage response, and variations in microRNA expression. These findings likely contribute, in part, to dysregulation of proliferation and apoptosis signaling pathways akin to what is observed in cancer; changes in cellular metabolism, metabolic flux, and mitochondrial function; and endothelial-to-mesenchymal transition as key signaling pathways that promote pulmonary vascular remodeling. This review will highlight recent advances in the field with an emphasis on the aforementioned molecular mechanisms as contributors to the pulmonary vascular disease pathophenotype.