The upregulation of miR-204-3p in LPS-induced acute lung injury aggravated pulmonary endothelial cells apoptosis via targeting sulfatase 2

Acute lung injury (ALI) results from the injury of alveolar epithelial cells and pulmonary capillary endothelial cells, with a high mortality rate ranging from 29% to 42%. Therefore, more efficient therapeutic strategies for ALI are necessary. Numerous studies revealed that miRNAs play a role in the regulation of ALI. Lipopolysaccharide (LPS) can induce an inflammatory response and has been widely applied in the establishment of the mouse ALI model. Here, we reported that miR-204-3p expression was upregulated by LPS treatment with increased cytokine secretion. LPS treatment promoted cell apoptosis, accompanied by abnormal cell structure and unobvious alveolar structure. These effects could be prevented by down-regulation of miR-204-3p, and promoted by miR-204-3p overexpression. Sulfatase 2 (SULF2) appeared to be the target of miR-204-3p predicted by TargetScan. Downregulation of miR-204-3p enhanced the protein level of SULF2, indicating that SULF2 was a target of miR-204-3p, which could negatively regulate the expression of SULF2. Thus, targeting miR-204-3p may be a potential therapeutic strategy for ALI.

FOXC2 Autoregulates Its Expression in the Pulmonary Endothelium After Endotoxin Stimulation in a Histone Acetylation-Dependent Manner

The innate immune response of pulmonary endothelial cells (EC) to lipopolysaccharide (LPS) induces Forkhead box protein C2 (FOXC2) activation through Toll Like Receptor 4 (TLR4). The mechanisms by which FOXC2 expression is regulated in lung EC under LPS stimulation remain unclear. We postulated that FOXC2 regulates its own expression in sepsis, and its transcriptional autoregulation directs lymphatic EC cell-fate decision. Bioinformatic analysis identified potential FOXC2 binding sites in the FOXC2 promoter. In human lung EC, we verified using chromatin immunoprecipitation (ChIP) and luciferase assays that FOXC2 bound to its own promoter and stimulated its expression after LPS stimulation. Chemical inhibition of histone acetylation by garcinol repressed LPS-induced histone acetylation in the FOXC2 promoter region, and disrupted LPS-mediated FOXC2 binding and transcriptional activation. CRISPR/dCas9/gRNA directed against FOXC2-binding-element (FBE) suppressed LPS-stimulated FOXC2 binding and autoregulation by blocking FBEs in the FOXC2 promoter, and repressed expression of lymphatic EC markers. In a neonatal mouse model of sterile sepsis, LPS-induced FOXC2 binding to FBE and FOXC2 expression in lung EC was attenuated with garcinol treatment. These data reveal a new mechanism of LPS-induced histone acetylation-dependent FOXC2 autoregulation.

Telomerase Prevents Emphysema in Old Mice by Sustaining Subpopulations of Endothelial and AT2 Cells

Accumulation of senescent cells has been causally linked to the development of age-related pathologies. Here, we characterized a new mouse model (p21+/Tert) whose telomerase (TERT) is expressed from the p21 promoter that can be activated in response to telomere dysfunction. Lung parenchyma from p21+/Tert old mice accumulated fewer senescent cells with age and this correlated with a reduction in age-related alveolar space enlargement, a feature of pulmonary emphysema. This protection against emphysema depends on TERT catalytic activity and is associated with increased proliferation of pulmonary endothelial cells (EC) and capillary density. Single-cell RNA sequencing of lung cells revealed that TERT expression was associated with the enrichment of ECs expressing genes involved in vessel regeneration and in AT2 cells overexpressing S/G2M markers. These findings indicate that p21-promoter-dependent expression of catalytically active telomerase prevents emphysema by sustaining the proliferation of subclasses of EC and AT2 cells.

Telomerase Prevents Emphysema in Old Mice by Sustaining Subpopulations of Endothelial and AT2 Cells

Accumulation of senescent cells has been causally linked to the development of age-related pathologies. Here, we characterized a new mouse model (p21+/Tert) whose telomerase (TERT) is expressed from the p21 promoter that can be activated in response to telomere dysfunction. Lung parenchyma from p21+/Tert old mice accumulated fewer senescent cells with age and this correlated with a reduction in age-related alveolar space enlargement, a feature of pulmonary emphysema. This protection against emphysema depends on TERT catalytic activity and is associated with increased proliferation of pulmonary endothelial cells (EC) and capillary density. Single-cell RNA sequencing of lung cells revealed that TERT expression was associated with the enrichment of ECs expressing genes involved in vessel regeneration and in AT2 cells overexpressing airway epithelial cell and S/G2M markers. These findings indicate that p21-promoter-dependent expression of catalytically active telomerase prevents emphysema by sustaining the proliferation of subclasses of EC and AT2 cells.

Chronic Hypoxia Decreases Endothelial Connexin 40, Attenuates Endothelium‐Dependent Hyperpolarization–Mediated Relaxation in Small Distal Pulmonary Arteries, and Leads to Pulmonary Hypertension

Background Abnormal endothelial function in the lungs is implicated in the development of pulmonary hypertension; however, there is little information about the difference of endothelial function between small distal pulmonary artery (PA) and large proximal PA and their contribution to the development of pulmonary hypertension. Herein, we investigate endothelium‐dependent relaxation in different orders of PAs and examine the molecular mechanisms by which chronic hypoxia attenuates endothelium‐dependent pulmonary vasodilation, leading to pulmonary hypertension. Methods and Results Endothelium‐dependent relaxation in large proximal PAs (second order) was primarily caused by releasing NO from the endothelium, whereas endothelium‐dependent hyperpolarization (EDH)–mediated vasodilation was prominent in small distal PAs (fourth–fifth order). Chronic hypoxia abolished EDH‐mediated relaxation in small distal PAs without affecting smooth muscle–dependent relaxation. RNA‐sequencing data revealed that, among genes related to EDH, the levels of Cx37 , Cx40 , Cx43 , and IK were altered in mouse pulmonary endothelial cells isolated from chronically hypoxic mice in comparison to mouse pulmonary endothelial cells from normoxic control mice. The protein levels were significantly lower for connexin 40 (Cx40) and higher for connexin 37 in mouse pulmonary endothelial cells from hypoxic mice than normoxic mice. Cx40 knockout mice exhibited significant attenuation of EDH‐mediated relaxation and marked increase in right ventricular systolic pressure. Interestingly, chronic hypoxia led to a further increase in right ventricular systolic pressure in Cx40 knockout mice without altering EDH‐mediated relaxation. Furthermore, overexpression of Cx40 significantly decreased right ventricular systolic pressure in chronically hypoxic mice. Conclusions These data suggest that chronic hypoxia‐induced downregulation of endothelial Cx40 results in impaired EDH‐mediated relaxation in small distal PAs and contributes to the development of pulmonary hypertension.