Platelet glycolytic metabolism correlates with hemodynamic severity in pulmonary arterial hypertension

Research progress of megakaryocytes and platelets in lung injury

The lung is an important site of extramedullary platelet formation, and megakaryocytes in the lung participate in immune responses in addition to platelet production. In acute lung injury and chronic lung injury, megakaryocytes and platelets play a promoting or protective role through different mechanisms. The authors reviewed the role of megakaryocytes and platelets in common clinical lung injuries with different course of disease and different pathogenic factors in order to provide new thinking for the diagnosis and treatment of lung injuries.

Assessing causal associations of blood counts and biochemical indicators with pulmonary arterial hypertension: a Mendelian randomization study and results from national health and nutrition examination survey 2003-2018

Background

Blood counts and biochemical markers are among the most common tests performed in hospitals and most readily accepted by patients, and are widely regarded as reliable biomarkers in the literature. The aim of this study was to assess the causal relationship between blood counts, biochemical indicators and pulmonary arterial hypertension (PAH).

Methods

A two-sample Mendelian randomization (MR) analysis was performed to assess the causal relationship between blood counts and biochemical indicators with PAH. The genome-wide association study (GWAS) for blood counts and biochemical indicators were obtained from the UK Biobank (UKBB), while the GWAS for PAH were sourced from the FinnGen Biobank. Inverse variance weighting (IVW) was used as the primary analysis method, supplemented by three sensitivity analyses to assess the robustness of the results. And we conducted an observational study using data from National Health and Nutrition Examination Survey (NHANES) 2003-2018 to verify the relationship.

Results

The MR analysis primarily using the IVW method revealed genetic variants of platelet count (OR=2.51, 95% CI 1.56-4.22, P<0.001), platelet crit(OR=1.87, 95% CI1.17-7.65, P=0.022), direct bilirubin (DBIL)(OR=1.71, 95%CI 1.18-2.47,P=0.004), insulin-like growth factor (IGF-1)(OR=0.51, 95% CI 0.27-0.96, P=0.038), Lipoprotein A (Lp(a))(OR=0.66, 95% CI 0.45-0.98, P=0.037) and total bilirubin (TBIL)(OR=0.51, 95% CI 0.27-0.96, P=0.038) were significantly associated with PAH. In NHANES, multivariate logistic regression analyses revealed a significant positive correlation between platelet count and volume and the risk of PAH, and a significant negative correlation between total bilirubin and PAH.

Conclusion

Our study reveals a causal relationship between blood counts, biochemical indicators and pulmonary arterial hypertension. These findings offer novel insights into the etiology and pathological mechanisms of PAH, and emphasizes the important value of these markers as potential targets for the prevention and treatment of PAH.

Analysis of Cellular Stress Assay Parameters and Intracellular ATP in Platelets: Comparison of Platelet Preparation Methods

Platelets are metabolically active, anucleated and small circulating cells mainly responsible for the prevention of bleeding and maintenance of hemostasis. Previous studies showed that platelets mitochondrial content, function, and energy supply change during several diseases such as HIV/AIDS, COVID-19, pulmonary arterial hypertension, and in preeclampsia during pregnancy. These changes in platelets contributed to the severity of diseases and mortality. In our previous studies, we have shown that the seahorse-based cellular stress assay (CSA) parameters are crucial to the understanding of the mitochondrial performance in peripheral blood mononuclear cells (PBMCS). Moreover, the results of CSA parameters were significantly influenced by the PBMC preparation methods. In this study, we assessed the correlation of CSA parameters and intracellular ATP content in platelets and evaluated the effects of platelet preparation methods on the results of CSA parameters and intracellular ATP content. We compared the results of CSA parameters and intracellular ATP content in platelets isolated by density centrifugation with Optiprep and simple centrifugation of blood samples without Optiprep. Platelets isolated by centrifugation with Optiprep showed a higher spare capacity, basal respiration, and maximal respiration than those isolated without Optiprep. There was a clear correlation between basal respiration and maximal respiration, and the whole-ATP content in both isolation methods. Moreover, a positive correlation was observed between the relative spare capacity and whole-cell ATP content. In conclusion, the results of seahorse-based CSA parameters and intracellular ATP content in platelets are markedly influenced by the platelet isolation methods employed. The results of basal respiration and maximal respiration are hallmarks of cellular activity in platelets, and whole-cell ATP content is a potential hint for basic platelet viability. We recommend further studies to evaluate the role of CSA parameters and intracellular ATP content in platelets as biomarkers for the diagnosis and prediction of disease states.

The Effect of Adjuvant Therapy with Molecular Hydrogen on Endogenous Coenzyme Q10 Levels and Platelet Mitochondrial Bioenergetics in Patients with Non-Alcoholic Fatty Liver Disease

Molecular hydrogen (H2) has been recognized as a novel medical gas with antioxidant and anti-inflammatory effects. Non-alcoholic fatty liver disease (NAFLD) is a liver pathology with increased fat accumulation in liver tissue caused by factors other than alcohol consumption. Platelet mitochondrial function is considered to reflect systemic mitochondrial health. We studied the effect of adjuvant therapy with hydrogen-rich water (HRW) on coenzyme Q10 (CoQ10) content and platelet mitochondrial bioenergetics in patients with NAFLD. A total of 30 patients with NAFLD and 15 healthy volunteers were included in this clinical trial. A total of 17 patients (H2 group) drank water three × 330 mL/day with tablets producing HRW (>4 mg/L H2) for 8 weeks, and 13 patients (P group) drank water with placebo tablets producing CO2. The concentration of CoQ10-TOTAL was determined by the HPLC method, the parameter of oxidative stress, thiobarbituric acid reactive substances (TBARS), by the spectrophotometric method, and mitochondrial bioenergetics in platelets isolated from whole blood by high-resolution respirometry. The patients with NAFLD had lower concentrations of CoQ10-TOTAL in the blood, plasma, and platelets vs. the control group. Mitochondrial CI-linked LEAK respiration was higher, and CI-linked oxidative phosphorylation (OXPHOS) and CII-linked electron transfer (ET) capacities were lower vs. the control group. Plasma TBARS concentrations were higher in the H2 group. After 8 weeks of adjuvant therapy with HRW, the concentration of CoQ10 in platelets increased, plasma TBARS decreased, and the efficiency of OXPHOS improved, while in the P group, the changes were non-significant. Long-term supplementation with HRW could be a promising strategy for the acceleration of health recovery in patients with NAFLD. The application of H2 appears to be a new treatment strategy for targeted therapy of mitochondrial disorders. Additional and longer-term studies are needed to confirm and elucidate the exact mechanisms of the mitochondria-targeted effects of H2 therapy in patients with NAFLD.

Platelet Metabolic Flexibility: A Matter of Substrate and Location

Platelets are cellular elements that are physiologically involved in hemostasis, inflammation, thrombotic events, and various human diseases. There is a link between the activation of platelets and their metabolism. Platelets possess considerable metabolic versatility. Although the role of platelets in hemostasis and inflammation is known, our current understanding of platelet metabolism in terms of substrate preference is limited. Platelet activation triggers an oxidative metabolism increase to sustain energy requirements better than aerobic glycolysis alone. In addition, platelets possess extra-mitochondrial oxidative phosphorylation, which could be one of the sources of chemical energy required for platelet activation. This review aims to provide an overview of flexible platelet metabolism, focusing on the role of metabolic compartmentalization in substrate preference, since the metabolic flexibility of stimulated platelets could depend on subcellular localization and functional timing. Thus, developing a detailed understanding of the link between platelet activation and metabolic changes is crucial for improving human health.

Vascular pathobiology of pulmonary hypertension

Pulmonary hypertension (PH), increased blood pressure in the pulmonary arteries, is a morbid and lethal disease. PH is classified into several groups based on etiology, but pathological remodeling of the pulmonary vasculature is a common feature. Endothelial cell dysfunction and excess smooth muscle cell proliferation and migration are central to the vascular pathogenesis. In addition, other cell types, including fibroblasts, pericytes, inflammatory cells and platelets contribute as well. Herein, we briefly note most of the main cell types active in PH and for each cell type, highlight select signaling pathway(s) highly implicated in that cell type in this disease. Among others, the role of hypoxia-inducible factors, growth factors (e.g., vascular endothelial growth factor, platelet-derived growth factor, transforming growth factor-β and bone morphogenetic protein), vasoactive molecules, NOTCH3, Kruppel-like factor 4 and forkhead box proteins are discussed. Additionally, deregulated processes of endothelial-to-mesenchymal transition, extracellular matrix remodeling and intercellular crosstalk are noted. This brief review touches upon select critical facets of PH pathobiology and aims to incite further investigation that will result in discoveries with much-needed clinical impact for this devastating disease.

Comprehensive analysis and validation of novel immune and vascular remodeling related genes signature associated with drug interactions in pulmonary arterial hypertension

Background: Previous studies revealed that the gene signatures are associated with the modulation and pathogenesis of pulmonary arterial hypertension (PAH). However, identifying critical transcriptional signatures in the blood of PAH patients remains lacking. Methods: The differentially expressed transcriptional signatures in the blood of PAH patients were identified by a meta-analysis from four microarray datasets. Then we investigated the enrichment of gene ontology and KEGG pathways and identified top hub genes. Besides, we investigated the correlation of crucial hub genes with immune infiltrations, hallmark gene sets, and blood vessel remodeling genes. Furthermore, we investigated the diagnostic efficacy of essential hub genes and their expression validation in an independent cohort of PAH, and we validate the expression level of hub genes in monocrotaline (MCT) induced PAH rats' model. Finally, we have identified the FDA-approved drugs that target the hub genes and their molecular docking. Results: We found 1,216 differentially expressed genes (DEGs), including 521 up-regulated and 695 down-regulated genes, in the blood of the PAH patients. The up-regulated DEGs are significantly associated with the enrichment of KEGG pathways mainly involved with immune regulation, cellular signaling, and metabolisms. We identified 13 master transcriptional regulators targeting the dysregulated genes in PAH. The STRING-based investigation identified the function of hub genes associated with multiple immune-related pathways in PAH. The expression levels of RPS27A, MAPK1, STAT1, RPS6, FBL, RPS3, RPS2, and GART are positively correlated with ssGSEA scores of various immune cells as positively correlated with the hallmark of oxidative stress. Besides, we found that these hub genes also regulate the vascular remodeling in PAH. Furthermore, the expression levels of identified hub genes showed good diagnostic efficacy in the blood of PAH, and we validated most of the hub genes are consistently dysregulated in an independent PAH cohort. Validation of hub genes expression level in the monocrotaline (MCT)-induced lung tissue of rats with PAH revealed that 5 screened hub genes (MAPK1, STAT1, TLR4, TLR2, GART) are significantly highly expressed in PAH rats, and 4 screened hub genes (RPS6, FBL, RPS3, and RPS2) are substantially lowly expressed in rats with PAH. Finally, we analyzed the interaction of hub proteins and FDA-approved drugs and revealed their molecular docking, and the results showed that MAPK1, TLR4, and GART interact with various drugs with appropriate binding affinity. Conclusion: The identified blood-derived key transcriptional signatures significantly correlate with immune infiltrations, hypoxia, glycolysis, and blood vessel remodeling genes. These findings may provide new insight into the diagnosis and treatment of PAH patients.

3'UTR shortening of HAS2 promotes hyaluronan hyper-synthesis and bioenergetic dysfunction in pulmonary hypertension

Pulmonary hypertension (PH) comprises a diverse group of disorders that share a common pathway of pulmonary vascular remodeling leading to right ventricular failure. Development of anti-remodeling strategies is an emerging frontier in PH therapeutics that requires a greater understanding of the interactions between vascular wall cells and their extracellular matrices. The ubiquitous matrix glycan, hyaluronan (HA), is markedly elevated in lungs from patients and experimental models with PH. Herein, we identified HA synthase-2 (HAS2) in the pulmonary artery smooth muscle cell (PASMC) layer as a predominant locus of HA dysregulation. HA upregulation involves depletion of NUDT21, a master regulator of alternative polyadenylation, resulting in 3'UTR shortening and hyper-expression of HAS2. The ensuing increase of HAS2 and hyper-synthesis of HA promoted bioenergetic dysfunction of PASMC characterized by impaired mitochondrial oxidative capacity and a glycolytic shift. The resulting HA accumulation stimulated pro-remodeling phenotypes such as cell proliferation, migration, apoptosis-resistance, and stimulated pulmonary artery contractility. Transgenic mice, mimicking HAS2 hyper-synthesis in smooth muscle cells, developed spontaneous PH, whereas targeted deletion of HAS2 prevented experimental PH. Pharmacological blockade of HAS2 restored normal bioenergetics in PASMC, ameliorated cell remodeling phenotypes, and reversed experimental PH in vivo. In summary, our results uncover a novel mechanism of HA hyper-synthesis and downstream effects on pulmonary vascular cell metabolism and remodeling.

Effect of Low-Dose Persistent Organic Pollutants on Mitochondrial Function: Human and in Vitro Evidence

BACKGROUND

Chronic exposure to low-dose persistent organic pollutants (POPs) can induce mitochondrial dysfunction. This study evaluated the association between serum POP concentrations and oxygen consumption rate (OCR) as a marker of mitochondrial function in humans and in vitro cells.

METHODS

Serum concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were measured in 323 adults. The OCRs of platelets and peripheral blood mononuclear cells (PBMCs) were assessed in 20 mL of fresh blood using a Seahorse XF analyzer. Additionally, the in vitro effects of Arochlor-1254, β-hexachlorocyclohexane, and p,p´-dichlorodiphenyltrichloroethane at concentrations of 0.1 pM to 100 nM were evaluated in human platelets, human PBMCs, and Jurkat T-cells.

RESULTS

The association between serum POP concentrations and OCR differed depending on the cell type. As serum OCP concentrations increased, basal platelet OCR levels decreased significantly; according to the OCP quintiles of summary measure, they were 8.6, 9.6, 8.2, 8.0, and 7.1 pmol/min/μg (P trend=0.005). Notably, the basal PBMC OCR levels decreased remarkably as the serum PCB concentration increased. PBMC OCR levels were 46.5, 34.3, 29.1, 16.5, and 13.1 pmol/min/μg according to the PCB quintiles of summary measure (P trend <0.001), and this inverse association was consistently observed in all subgroups stratified by age, sex, obesity, type 2 diabetes mellitus, and hypertension, respectively. In vitro experimental studies have also demonstrated that chronic exposure to low-dose POPs could decrease OCR levels.

CONCLUSION

The findings from human and in vitro studies suggest that chronic exposure to low-dose POPs can induce mitochondrial dysfunction by impairing oxidative phosphorylation.

Platelet-Derived TGF (Transforming Growth Factor)-β1 Enhances the Aerobic Glycolysis of Pulmonary Arterial Smooth Muscle Cells by PKM2 Upregulation

BACKGROUND

Metabolic reprogramming is a hallmark of pulmonary arterial hypertension. Platelet activation has been implicated in pulmonary arterial hypertension (PAH), whereas the role of platelet in the pathogenesis of PAH remains unclear.

METHODS

First, we explored the platelet function of SU5416/hypoxia mice and monocrotaline-injected rats PAH model. Then we investigated pulmonary arterial smooth muscle cell aerobic glycolysis after being treated with platelet supernatant. TGF (transforming growth factor)-βRI, PKM2, and other antagonists were applied to identify the underlying mechanism. In addition, platelet-specific deletion TGF-β1 mice were exposed to chronic hypoxia and SU5416. Cardiopulmonary hemodynamics, vascular remodeling, and aerobic glycolysis of pulmonary arterial smooth muscle cell were determined.

RESULTS

Here, we demonstrate that platelet-released TGF-β1 enhances the aerobic glycolysis of pulmonary arterial smooth muscle cells after platelet activation via increasing PKM2 expression. Mechanistically, platelet-derived TGF-β1 regulates PKM2 expression through mTOR (mammalian target of rapamycin)/c-Myc/PTBP1-hnRNPA1 pathway. Platelet TGF-β1 deficiency mice are significantly protected from SU5416 plus chronic hypoxia-induced PAH, including attenuated increases in right ventricular systolic pressure and less pulmonary vascular remodeling. Also, in Pf4cre⁺ Tgfb1^fl/fl mice, pulmonary arterial smooth muscle cells showed lower glycolysis capacity and their PKM2 expression decreased.

CONCLUSIONS

Our data demonstrate that TGF-β1 released by platelet contributes to the pathogenesis of PAH and further highlights the role of platelet in PAH.

Isotopically nonstationary 13C metabolic flux analysis in resting and activated human platelets

Platelet metabolism is linked to platelet hyper- and hypoactivity in numerous human diseases. Developing a detailed understanding of the link between metabolic shifts and platelet activation state is integral to improving human health. Here, we show the first application of isotopically nonstationary ¹³C metabolic flux analysis to quantitatively measure carbon fluxes in both resting and thrombin activated platelets. Metabolic flux analysis results show that resting platelets primarily metabolize glucose to lactate via glycolysis, while acetate is oxidized to fuel the tricarboxylic acid cycle. Upon activation with thrombin, a potent platelet agonist, platelets increase their uptake of glucose 3-fold. This results in an absolute increase in flux throughout central metabolism, but when compared to resting platelets they redistribute carbon dramatically. Activated platelets decrease relative flux to the oxidative pentose phosphate pathway and TCA cycle from glucose and increase relative flux to lactate. These results provide the first report of reaction-level carbon fluxes in platelets and allow us to distinguish metabolic fluxes with much higher resolution than previous studies.

Platelets, extracellular vesicles and coagulation in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare disease of the pulmonary vasculature, characterised pathologically by proliferation, remodelling and thrombosis in situ. Unfortunately, existing therapeutic interventions do not reverse these findings and the disease continues to result in significant morbidity and premature mortality. A number of haematological derangements have been described in pulmonary arterial hypertension which may provide insights into the pathobiology of the disease and opportunities to explore new therapeutic pathways. These include quantitative and qualitative platelet abnormalities, such as thrombocytopaenia, increased mean platelet volume and altered platelet bioenergetics. Furthermore, a hypercoagulable state and aberrant negative regulatory pathways can be observed, which could contribute to thrombosis in situ in distal pulmonary arteries and arterioles. Finally, there is increasing interest in the role of extracellular vesicle autocrine and paracrine signalling in pulmonary arterial hypertension, and their potential utility as biomarkers and novel therapeutic targets. This review focuses on the potential role of platelets, extracellular vesicles and coagulation pathways in the pathobiology of pulmonary arterial hypertension. We highlight important unanswered clinical questions and the implications of these observations for future research and pulmonary arterial hypertension-directed therapies.

Disease-specific platelet signaling defects in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a rapidly progressive disease with several treatment options. Long-term mortality remains high with great heterogeneity in treatment response. Even though most of the pathology of IPAH is observed in the lung, there is systemic involvement. Platelets from patients with IPAH have characteristic metabolic shifts and defects in activation; therefore, we investigated whether they could be used to identify other disease-specific abnormalities. We used proteomics to investigate protein expression changes in platelets from patients with IPAH compared with healthy controls. Key abnormalities of nitric oxide pathway were tested in platelets from a larger cohort of unique patients with IPAH. Platelets showed abnormalities in the prostacyclin and nitric oxide pathways, which are dysregulated in IPAH and hence targets of therapy. We detected reduced expression of G protein αs and increased expression of the regulatory subunits of the cAMP-dependent protein kinase (PKA) type II isoforms, supporting an overall decrease in the activation of the prostacyclin pathway. We noted reduced levels of the soluble guanylate cyclase (sGC) subunits and increased expression of the phosphodiesterase type 5 A (PDE5A), conditions that affect the response to nitric oxide. Ensuing analysis of 38 unique patients with IPAH demonstrated considerable variation in the levels and specific activity of sGC, a finding with novel implications for personalized therapy. Platelets have some of the characteristic vasoactive signal abnormalities seen in IPAH and may provide comprehensive ex vivo mechanistic information to direct therapeutic decisions.