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Pulmonary artery smooth muscle cell (PA-SMC) proliferation and inflammation are key components of pulmonary arterial hypertension (PAH). Interleukin (IL)-1β binds to IL-1 receptor (R)1, thereby recruiting the molecular adaptor myeloid differentiation primary response protein 88 (MyD88) (involved in IL-1R1 and Toll-like receptor signal transduction) and inducing IL-1, IL-6 and tumour necrosis factor-α synthesis through nuclear factor-κB activation.We investigated the IL-1R1/MyD88 pathway in the pathogenesis of pulmonary hypertension.Marked IL-1R1 and MyD88 expression with predominant PA-SMC immunostaining was found in lungs from patients with idiopathic PAH, mice with hypoxia-induced pulmonary hypertension and SM22-5-HTT(+) mice. Elevations in lung IL-1β, IL-1R1, MyD88 and IL-6 preceded pulmonary hypertension in hypoxic mice. IL-1R1(-/-), MyD88(-/-) and control mice given the IL-1R1 antagonist anakinra were protected similarly against hypoxic pulmonary hypertension and perivascular macrophage recruitment. Anakinra reversed pulmonary hypertension partially in SM22-5-HTT(+) mice and markedly in monocrotaline-treated rats. IL-1β-mediated stimulation of mouse PA-SMC growth was abolished by anakinra and absent in IL-1R1(-/-) and MyD88(-/-) mice. Gene deletion confined to the myeloid lineage (M.lys-Cre MyD88(fl/fl) mice) decreased pulmonary hypertension severity versus controls, suggesting IL-1β-mediated effects on PA-SMCs and macrophages. The growth-promoting effect of media conditioned by M1 or M2 macrophages from M.lys-Cre MyD88(fl/fl) mice was attenuated.Pulmonary vessel remodelling and inflammation during pulmonary hypertension require IL-1R1/MyD88 signalling. Targeting the IL-1β/IL-1R1 pathway may hold promise for treating human PAH.

Macrophages are major players in the pathogenesis of pulmonary arterial hypertension (PAH).To investigate whether lung macrophages and pulmonary-artery smooth muscle cells (PASMCs) collaborate to stimulate PASMC growth and whether the CCL2-CCR2 and CCL5-CCR5 pathways inhibited macrophage–PASMC interactions and PAH development, we used human CCR5-knock-in mice and PASMCs from patients with PAH and controls.Conditioned media from murine M1 or M2 macrophages stimulated PASMC growth. This effect was markedly amplified with conditioned media from M2 macrophage/PASMC co-cultures. CCR2, CCR5, CCL2 and CCL5 were upregulated in macrophage/PASMC co-cultures. Compared to inhibiting either receptor, dual CCR2 and CCR5 inhibition more strongly attenuated the growth-promoting effect of conditioned media from M2-macrophage/PASMC co-cultures. Deleting either CCR2 or CCR5 in macrophages or PASMCs attenuated the growth response. In mice with hypoxia- or SUGEN/hypoxia-induced PH, targeting both CCR2 and CCR5 prevented or reversed PH more efficiently than targeting either receptor alone. Patients with PAH exhibited CCR2 and CCR5 upregulation in PASMCs and perivascular macrophages compared to controls. The PASMC growth-promoting effect of conditioned media from M2-macrophage/PASMC co-cultures was greater when PASMCs from PAH patients were used in the co-cultures or as the target cells and was dependent on CCR2 and CCR5. PASMC migration toward M2-macrophages was greater with PASMCs from PAH patients and was attenuated by blocking CCR2 and CCR5.CCR2 and CCR5 are required for collaboration between macrophages and PASMCs to initiate and amplify PASMC migration and proliferation during PAH development. Dual targeting of CCR2 and CCR5 may hold promise for treating human PAH.

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Background: Aging myocardium undergoes progressive cardiac hypertrophy and interstitial fibrosis with diastolic and systolic dysfunction. Recent metabolomics studies shed light on amino acids in aging. The present study aimed to dissect how aging leads to elevated plasma levels of the essential amino acid phenylalanine (Phe) and how it may promote age-related cardiac dysfunction. Methods: We studied cardiac structure and function, together with Phe catabolism in wild-type (WT) and p21 -/- mice (male; 2 to 24 months), the latter known to be protected from cellular senescence. To explore Phe's effects on cellular senescence and ectopic Phe catabolism we treated cardiomyocytes (primary adult rat or human AC-16) with Phe. To establish a role for Phe in driving cardiac aging, WT male mice were treated twice a day with Phe (200 mg/kg) for a month. We also treated aged WT mice with tetrahydrobiopterin (BH4; 10 mg/kg), the essential cofactor for the Phe-degrading enzyme phenylalanine hydroxylase (PAH), or restricted dietary Phe intake. The impact of senescence on hepatic Phe catabolism was explored in vitro in AML12 hepatocytes treated with Nutlin3a (a p53 activator), with or without p21-targeting siRNA or BH4, with quantification of PAH and tyrosine levels. Results: Natural aging is associated with a progressive increase in plasma Phe levels concomitant with cardiac dysfunction, whilst p21 deletion delayed these changes. Phe treatment induced premature cardiac deterioration in young WT mice, strikingly akin to that occurring with aging, whilst triggering cellular senescence, redox and epigenetic changes. Pharmacological restoration of Phe catabolism with BH4 administration or dietary Phe restriction abrogated the rise in plasma Phe and reversed cardiac senescent alterations in aged WT mice. Observations from aged mice and human samples implicated age-related decline in hepatic Phe catabolism as a key driver of elevated plasma Phe levels and showed increased myocardial PAH-mediated Phe catabolism, a novel signature of cardiac aging. Conclusions: Our findings establish a pathogenic role for increased Phe levels in cardiac aging, linking plasma Phe levels to cardiac senescence via dysregulated Phe catabolism along a hepatic-cardiac axis. They highlight Phe/PAH modulation as a potential therapeutic strategy for age-associated cardiac impairment.

BACKGROUND: Senescent cells (SCs) are involved in proliferative disorders, but their role in pulmonary hypertension remains undefined. We investigated SCs in patients with pulmonary arterial hypertension and the role of SCs in animal pulmonary hypertension models. METHODS: We investigated senescence (p16, p21) and DNA damage (γ-H2AX, 53BP1) markers in patients with pulmonary arterial hypertension and murine models. We monitored p16 activation by luminescence imaging in p16-luciferase (p16 LUC/+ ) knock-in mice. SC clearance was obtained by a suicide gene (p16 promoter–driven killer gene construct in p16-ATTAC mice), senolytic drugs (ABT263 and cell-permeable FOXO4-p53 interfering peptide [FOXO4-DRI]), and p16 inactivation in p16 LUC/LUC mice. We investigated pulmonary hypertension in mice exposed to normoxia, chronic hypoxia, or hypoxia+Sugen, mice overexpressing the serotonin transporter (SM22-5-HTT + ), and rats given monocrotaline. RESULTS: Patients with pulmonary arterial hypertension compared with controls exhibited high lung p16, p21, and γ-H2AX protein levels, with abundant vascular cells costained for p16, γ-H2AX, and 53BP1. Hypoxia increased thoracic bioluminescence in p16 LUC/+ mice. In wild-type mice, hypoxia increased lung levels of senescence and DNA-damage markers, senescence-associated secretory phenotype components, and p16 staining of pulmonary endothelial cells (P-ECs, 30% of lung SCs in normoxia), and pulmonary artery smooth muscle cells. SC elimination by suicide gene or ABT263 increased the right ventricular systolic pressure and hypertrophy index, increased vessel remodeling (higher dividing proliferating cell nuclear antigen–stained vascular cell counts during both normoxia and hypoxia), and markedly decreased lung P-ECs. Pulmonary hemodynamic alterations and lung P-EC loss occurred in older p16 LUC/LUC mice, wild-type mice exposed to Sugen or hypoxia+Sugen, and SM22-5-HTT + mice given either ABT263 or FOXO4-DRI, compared with relevant controls. The severity of monocrotaline-induced pulmonary hypertension in rats was decreased slightly by ABT263 for 1 week but was aggravated at 3 weeks, with loss of P-ECs. CONCLUSION: Elimination of senescent P-ECs by senolytic interventions may worsen pulmonary hemodynamics. These results invite consideration of the potential impact on pulmonary vessels of strategies aimed at controlling cell senescence in various contexts.

RationaleCell senescence is a key process in age-associated dysfunction and diseases, notably chronic obstructive pulmonary disease (COPD). We previously identified phospholipase A2-receptor 1 (PLA2R1) as a positive regulator of cell senescence acting via JAK/STAT signalling. Its role in pathology, however, remains unknown. Here, we assessed PLA2R1-induced senescence in COPD and lung emphysema pathogenesis.MethodsAssessment of cell senescence in lungs and cultured lung cells from patients with COPD and controls subjected to PLA2R1 knock-down, PLA2R1 gene transduction and treatment with the JAK1/2 inhibitor ruxolitinib. To assess whether PLA2R1 upregulation caused lung lesions, we developed transgenic mice overexpressing PLA2R1 (PLA2R1-TG) and intratracheally injected wild-type mice with a lentiviral vector carrying the PLA2R1 gene (LV-PLA2R1 mice).Measurements and ResultsWe found that PLA2R1 was overexpressed in various cell types exhibiting senescence characteristics in COPD lungs. PLA2R1 knockdown extended the population doubling capacity of these cells and inhibited their proinflammatory senescence-associated secretory phenotype (SASP). PLA2R1-mediated cell senescence in COPD was largely reversed by treatment with the potent JAK1/2 inhibitor ruxolitinib. 5 month-old PLA2R1-TG mice exhibited lung-cell senescence and developed lung emphysema and lung fibrosis together with pulmonary hypertension. Treatment with ruxolitinib induced reversal of lung emphysema and fibrosis. LV-PLA2R1-treated mice developed lung emphysema within 4 weeks, and this was markedly attenuated by concomitant ruxolitinib treatment.ConclusionOur data support a major role for PLA2R1 activation in driving lung-cell senescence and lung alterations in COPD. Targeting JAK1/2 may represent a promising therapeutic approach for COPD.

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