Novel large-particle FACS purification of adult ventricular myocytes reveals accumulation of myosin and actin disproportionate to cell size and proteome in normal post-weaning development.

RATIONALE: Quantifying cellular proteins in ventricular myocytes (MCs) is challenging due to tissue heterogeneity and the variety of cell sizes in the heart. In post-weaning cardiac ontogeny, rod-shaped MCs make up the majority of the cardiac mass while remaining a minority of cardiac cells in number. Current biochemical analyses of cardiac proteins do not correlate well the content of MC-specific proteins to cell type or size in normally developing tissue. OBJECTIVE: To develop a new large-particle fluorescent-activated cell sorting (LP-FACS) strategy for the purification of adult rod-shaped MCs. This approach is developed to enable growth-scaled measurements per-cell of the MC proteome and sarcomeric proteins (i.e. myosin heavy chain (MyHC) and alpha-actin (α-actin)) content. METHODS AND RESULTS: Individual cardiac cells were isolated from 21 to 94days old mice. An LP-FACS jet-in-air system with a 200-µm nozzle was defined for the first time to purify adult MCs. Cell-type specific immunophenotyping and sorting yielded ≥95% purity of adult MCs independently of cell morphology and size. This approach excluded other cell types and tissue contaminants from further analysis. MC proteome, MyHC and α-actin proteins were measured in linear biochemical assays normalized to cell numbers. Using the allometric coefficient α, we scaled the MC-specific rate of protein accumulation to growth post-weaning. MC-specific volumes (α=1.02) and global protein accumulation (α=0.94) were proportional (i.e. isometric) to body mass. In contrast, MyHC and α-actin accumulated at a much greater rate (i.e. hyperallometric) than body mass (α=1.79 and 2.19 respectively) and MC volumes (α=1.76 and 1.45 respectively). CONCLUSION: Changes in MC proteome and cell volumes measured in LP-FACS purified MCs are proportional to body mass post-weaning. Oppositely, MyHC and α-actin are concentrated more rapidly than what would be expected from MC proteome accumulation, cell enlargement, or animal growth alone. LP-FACS provides a new standard for adult MC purification and an approach to scale the biochemical content of specific proteins or group of proteins per cell in enlarging MCs.

Mice with Genetic Deletion of Group VIA Phospholipase A2ß Exhibit Impaired Macrophage Function and Increased Parasite Load in Trypanosoma cruzi-Induced Myocarditis.

Trypanosoma cruzi infection, which is the etiological agent of Chagas disease, is associated with intense inflammation during the acute and chronic phases. The pathological progression of Chagas disease is influenced by the infiltration and transmigration of inflammatory cells across the endothelium to infected tissues, which are carefully regulated processes involving several molecular mediators, including adhesion molecules and platelet-activating factor (PAF). We have shown that PAF production is dependent upon calcium-independent group VIA phospholipase A2ß (iPLA2ß) following infection of human coronary artery endothelial cells (HCAECs) with T. cruzi, suggesting that the absence of iPLA2ß may decrease the recruitment of inflammatory cells to the heart to manage parasite accumulation. Cardiac endothelial cells isolated from iPLA2ß-knockout (iPLA2ß-KO) mice infected withT. cruzi demonstrated decreased PAF production compared to that by cells isolated from wild-type (WT) mice but demonstrated increases in adhesion molecule expression similar to those seen in WT mice. Myocardial inflammation in iPLA2ß-KO mice infected with T. cruzi was similar in severity to that in WT mice, but the iPLA2ß-KO mouse myocardium contained more parasite pseudocysts. Upon activation, macrophages from iPLA2ß-KO mice produced significantly less nitric oxide (NO) and caused lessT. cruzi inhibition than macrophages from wild-type mice. Thus, the absence of iPLA2ß activity does not influence myocardial inflammation, but iPLA2ß is essential forT. cruzi clearance.

The absence of myocardial calcium-independent phospholipase A2γ results in impaired prostaglandin E2 production and decreased survival in mice with acute Trypanosoma cruzi infection.

Cardiomyopathy is a serious complication of Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi. The parasite often infects cardiac myocytes, causing the release of inflammatory mediators, including eicosanoids. A recent study from our laboratory demonstrated that calcium-independent phospholipase A2γ (iPLA2γ) accounts for the majority of PLA2 activity in rabbit ventricular myocytes and is responsible for arachidonic acid (AA) and prostaglandin E2 (PGE2) release. Thus, we hypothesized that cardiac iPLA2γ contributes to eicosanoid production in T. cruzi infection. Inhibition of the isoform iPLA2γ or iPLA2ß, with the R or S enantiomer of bromoenol lactone (BEL), respectively, demonstrated that iPLA2γ is the predominant isoform in immortalized mouse cardiac myocytes (HL-1 cells). Stimulation of HL-1 cells with thrombin, a serine protease associated with microthrombus formation in Chagas' disease and a known activator of iPLA2, increased AA and PGE2 release, accompanied by platelet-activating factor (PAF) production. Similarly, T. cruzi infection resulted in increased AA and PGE2 release over time that was inhibited by pretreatment with (R)-BEL. Further, T. cruzi-infected iPLA2γ-knockout (KO) mice had lower survival rates and increased tissue parasitism compared to wild-type (WT) mice, suggesting that iPLA2γ-KO mice were more susceptible to infection than WT mice. A significant increase in iPLA2 activity was observed in WT mice following infection, whereas iPLA2γ-KO mice showed no alteration in cardiac iPLA2 activity and produced less PGE2. In summary, these studies demonstrate that T. cruzi infection activates cardiac myocyte iPLA2γ, resulting in increased AA and PGE2 release, mediators that may be essential for host survival during acute infection. Thus, these studies suggest that iPLA2γ plays a cardioprotective role during the acute stage of Chagas' disease.

Lung endothelial cell platelet-activating factor production and inflammatory cell adherence are increased in response to cigarette smoke component exposure.

An early event in the pathogenesis of emphysema is the development of inflammation associated with accumulation of polymorphonuclear leukocytes (PMN) in small airways, and inflammatory cell recruitment from the circulation involves migration across endothelial and epithelial cell barriers. Platelet-activating factor (PAF) promotes transendothelial migration in several vascular beds, and we postulated that increased PAF production in the airways of smokers might enhance inflammatory cell recruitment and exacerbate inflammation. To examine this possibility, we incubated human lung microvascular endothelial cells (HMVEC-L) with cigarette smoke extract (CSE) and found that CSE inhibits PAF-acetylhydrolase (PAF-AH) activity. This enhances HMVEC-L PAF production and PMN adherence, and adherence is blocked by PAF receptor antagonists (CV3988 or ginkgolide B). CSE also inhibited PAF-AH activity of lung endothelial cells isolated from wild-type (WT) and iPLA(2)ß knockout mice, and with WT cells, CSE enhanced PAF production and RAW 264.7 cell adherence. In contrast, CSE did not affect PAF production or RAW 264.7 cell adherence to iPLA(2)ß-null cells, suggesting that iPLA(2)ß plays an important role in PAF production by lung endothelial cells. These findings suggest that inhibition of PAF-AH by components of cigarette smoke may initiate or exacerbate inflammatory lung disease by enhancing PAF production and promoting accumulation of inflammatory cells in small airways. In addition, iPLA(2)ß is identified as a potential target for therapeutic interventions to reduce airway inflammation and the progression of chronic lung disease.

Platelet-activating factor and metastasis: calcium-independent phospholipase A2ß deficiency protects against breast cancer metastasis to the lung.

We determined the contribution of calcium-independent phospholipase A(2)ß (iPLA(2)ß) to lung metastasis development following breast cancer injection into wild-type (WT) and iPLA(2)ß-knockout (iPLA(2)ß-KO) mice. WT and iPLA(2)ß-KO mice were injected in the mammary pad with 200,000 E0771 breast cancer cells. There was no difference in primary tumor size between WT and iPLA(2)ß-KO mice at 27 days postinjection. However, we observed an 11-fold greater number of breast cancer cells in the lungs of WT mice compared with iPLA(2)ß-KO animals (P < 0.05). Isolated WT lung endothelial cells demonstrated a significant increase in platelet-activating factor (PAF) production when stimulated with thrombin [1 IU/ml, 10 min, 4,330 ± 555 vs. 15,227 ± 1,043 disintegrations per minute (dpm), P < 0.01] or TNF-α (10 ng/ml, 2 h, 16,532 ± 538 dpm, P < 0.01). Adherence of E0771 cells to WT endothelial cells was increased by thrombin (4.8 ± 0.3% vs. 70.9 ± 6.3, P < 0.01) or TNF-α (60.5 ± 4.3, P < 0.01). These responses were blocked by pretreatment with the iPLA(2)ß-selective inhibitor (S)-bromoenol lactone and absent in lung endothelial cells from iPLA(2)ß-KO mice. These data indicate that endothelial cell iPLA(2)ß is responsible for PAF production and adherence of E0771 cells and may play a role in cancer cell migration to distal locations.

Activation of group VI phospholipase A2 isoforms in cardiac endothelial cells.

The endothelium comprises a cellular barrier between the circulation and tissues. We have previously shown that activation of protease-activated receptor 1 (PAR-1) and PAR-2 on the surface of human coronary artery endothelial cells by tryptase or thrombin increases group VIA phospholipase A(2) (iPLA(2)ß) activity and results in production of multiple phospholipid-derived inflammatory metabolites. We isolated cardiac endothelial cells from hearts of iPLA(2)ß-knockout (iPLA(2)ß-KO) and wild-type (WT) mice and measured arachidonic acid (AA), prostaglandin I(2) (PGI(2)), and platelet-activating factor (PAF) production in response to PAR stimulation. Thrombin (0.1 IU/ml) or tryptase (20 ng/ml) stimulation of WT endothelial cells rapidly increased AA and PGI(2) release and increased PAF production. Selective inhibition of iPLA(2)ß with (S)-bromoenol lactone (5 µM, 10 min) completely inhibited thrombin- and tryptase-stimulated responses. Thrombin or tryptase stimulation of iPLA(2)ß-KO endothelial cells did not result in significant PAF production and inhibited AA and PGI(2) release. Stimulation of cardiac endothelial cells from group VIB (iPLA(2)γ)-KO mice increased PAF production to levels similar to those of WT cells but significantly attenuated PGI(2) release. These results indicate that cardiac endothelial cell PAF production is dependent on iPLA(2)ß activation and that both iPLA(2)ß and iPLA(2)γ may be involved in PGI(2) release.

Endothelial cell prostaglandin I(2) and platelet-activating factor production are markedly attenuated in the calcium-independent phospholipase A(2)beta knockout mouse.

Damage and activation of lung endothelium can lead to interstitial edema, infiltration of inflammatory cells into the interstitium and airways, and production of inflammatory metabolites, all of which propagate airway inflammation in a variety of diseases. We have previously determined that stimulation of human microvascular endothelial cells from lung (HMVEC-L) results in activation of a calcium-independent phospholipase A(2) (iPLA(2)), and this leads to arachidonic acid release and production of prostaglandin I(2) (PGI(2)) and platelet-activating factor (PAF). We stimulated lung endothelial cells isolated from iPLA(2)beta-knockout (KO) and wild type (WT) mice with thrombin and tryptase to determine the role of iPLA(2)beta in endothelial cell membrane phospholipid hydrolysis. Thrombin or tryptase stimulation of WT lung endothelial cells resulted in increased arachidonic acid release and production of PGI(2) and PAF. Arachidonic acid release and PGI(2) production by stimulated iPLA(2)beta-KO endothelial cells were significantly reduced compared to WT. Measured PLA(2) activity and PGI(2) production by iPLA(2)beta-KO cells were suppressed by pretreatment with (R)-bromoenol lactone (R-BEL), which is a selective inhibitor of iPLA2gamma. In contrast to the increase in PAF production induced by stimulation of WT endothelial cells, none was observed for KO cells, and this suggests that endothelial PAF production is entirely dependent on iPLA(2)beta activity. Because inflammatory cell recruitment involves the interaction of endothelial cell PAF with PAF receptors on circulating cells, these data suggest that iPLA(2)beta may be a suitable therapeutic target for the treatment of inflammatory lung diseases.

Highly efficient transfection of human induced pluripotent stem cells using magnetic nanoparticles.

PURPOSE: The delivery of transgenes into human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) represents an important tool in cardiac regeneration with potential for clinical applications. Gene transfection is more difficult, however, for hiPSCs and hiPSC-CMs than for somatic cells. Despite improvements in transfection and transduction, the efficiency, cytotoxicity, safety, and cost of these methods remain unsatisfactory. The objective of this study is to examine gene transfection in hiPSCs and hiPSC-CMs using magnetic nanoparticles (NPs). METHODS: Magnetic NPs are unique transfection reagents that form complexes with nucleic acids by ionic interaction. The particles, loaded with nucleic acids, can be guided by a magnetic field to allow their concentration onto the surface of the cell membrane. Subsequent uptake of the loaded particles by the cells allows for high efficiency transfection of the cells with nucleic acids. We developed a new method using magnetic NPs to transfect hiPSCs and hiPSC-CMs. HiPSCs and hiPSC-CMs were cultured and analyzed using confocal microscopy, flow cytometry, and patch clamp recordings to quantify the transfection efficiency and cellular function. RESULTS: We compared the transfection efficiency of hiPSCs with that of human embryonic kidney (HEK 293) cells. We observed that the average efficiency in hiPSCs was 43%±2% compared to 62%±4% in HEK 293 cells. Further analysis of the transfected hiPSCs showed that the differentiation of hiPSCs to hiPSC-CMs was not altered by NPs. Finally, robust transfection of hiPSC-CMs with an efficiency of 18%±2% was obtained. CONCLUSION: The difficult-to-transfect hiPSCs and hiPSC-CMs were efficiently transfected using magnetic NPs. Our study offers a novel approach for transfection of hiPSCs and hiPSC-CMs without the need for viral vector generation.

Absence of calcium-independent phospholipase A2 ß impairs platelet-activating factor production and inflammatory cell recruitment in Trypanosoma cruzi-infected endothelial cells.

Both acute and chronic phases of Trypanosoma cruzi (T. cruzi) infection are characterized by tissue inflammation, mainly in the heart. A key step in the inflammatory process is the transmigration of inflammatory cells across the endothelium to underlying infected tissues. We observed increased arachidonic acid release and platelet-activating factor (PAF) production in human coronary artery endothelial cells (HCAEC) at up to 96 h of T. cruzi infection. Arachidonic acid release is mediated by activation of the calcium-independent phospholipase A2 (iPLA2) isoforms iPLA2 ß and iPLA2 γ, whereas PAF production was dependent upon iPLA2 ß activation alone. Trypanosoma cruzi infection also resulted in increased cell surface expression of adhesion molecules. Increased adherence of inflammatory cells to T. cruzi-infected endothelium was blocked by inhibition of endothelial cell iPLA2 ß or by blocking the PAF receptor on inflammatory cells. This suggests that PAF, in combination with adhesion molecules, might contribute to parasite clearing in the heart by recruiting inflammatory cells to the endothelium.

PGE2 release from tryptase-stimulated rabbit ventricular myocytes is mediated by calcium-independent phospholipase A2γ.

Inflammation is associated with cardiovascular disease, including myocardial infarction, atherosclerosis, myocarditis and congestive heart failure. Mast cells have been implicated in inflammation, but their precise role in cardiac inflammation remains unclear. Mast cells contain a variety of pre-formed granule-associated mediators, including tryptase. We have previously demonstrated that the majority of the phospholipase A(2) (PLA(2)) activity in isolated rabbit ventricular myocytes is membrane-associated, calcium-independent and selective for plasmalogen phospholipids. We hypothesized that tryptase stimulation of rabbit ventricular myocytes would increase iPLA(2) activity, leading to increased arachidonic acid and prostaglandin E(2) (PGE(2)) release. Isolated rabbit ventricular myocytes were stimulated with tryptase and iPLA(2) activity, arachidonic acid and PGE(2) release were measured. Tryptase stimulation increased iPLA(2) activity after 5 min. Activation of iPLA(2) was accompanied by increased arachidonic acid and PGE(2) release in tryptase-stimulated myocytes. However no increase in platelet activating factor was observed with tryptase stimulation. To distinguish between different iPLA(2) isoforms in the myocardium, we pretreated ventricular myocytes with the (R)- and (S)-enantiomers of bromoenol lactone (BEL) to selectively inhibit iPLA(2)γ and ß respectively. Pretreatment with (R)-BEL resulted in complete inhibition of tryptase-stimulated iPLA(2) activity, arachidonic acid and PGE(2) release, suggesting the iPLA(2)γ is the predominant myocardial isoform activated by tryptase. These studies demonstrate that PGE(2) release from tryptase stimulated rabbit ventricular myocytes is mediated primarily by iPLA(2)γ.

Polymorphonuclear leukocytes isolated from umbilical cord blood as a useful research tool to study adherence to cell monolayers.

One of the initial steps in the inflammatory process involves the adherence and transmigration of circulating polymorphonuclear leukocytes (PMN) across the endothelial cell monolayer. One of the main constituents of the neutrophil phagosome that contributes to bacterial killing is myeloperoxidase (MPO) which can be measured spectrophotometrically, using hydrogen peroxide as a substrate, and hence can be used as an index to quantify neutrophil adherence. To evaluate whether PMN isolated from umbilical cord blood could be used for in vitro experiments to monitor neutrophil adherence, we compared the adherence to confluent endothelial and epithelial cell monolayers using PMN isolated from umbilical cord and adult peripheral blood. The extent of PMN adherence was assessed by measuring MPO activity. In initial experiments, we isolated PMN from umbilical cord and adult peripheral blood and measured MPO activity with respect to cell number and assay incubation times. Our data demonstrate that PMN obtained from either source had similar MPO activity and similar adherence to endothelial or epithelial cells. In conclusion, our data suggest that umbilical cord blood is a suitable source of leukocytes to examine PMN adherence in the setting of inflammation in a variety of disease processes.