B cell-specific knockout of AID protects against atherosclerosis.

Antigen-naive IgM-producing B cells are atheroprotective, whereas mature B cells producing class-switched antibodies promote atherosclerosis. Activation-induced cytidine deaminase (AID), which mediates class switch recombination (CSR), would thus be expected to foster atherosclerosis. Yet, AID also plays a major role in the establishment of B cell tolerance. We sought to define whether AID affects atherosclerotic plaque formation. We generated Ldlr-/- chimeras transplanted with bone marrow from Aicda-/- or wild-type (WT) mice, fed a HFD for 14 weeks. Decreased B cell maturation in Ldlr-/-Aicda-/- mice was demonstrated by 50% reduction in splenic and aortic BAFFR expression, a key signaling component of B2 cell maturation. This was associated with increased plasma IgM in Ldlr-/-Aicda-/- compared with Ldlr-/-WT animals. Importantly, Ldlr-/-Aicda-/- mice had reduced atherosclerotic lesion area (0.20 ± 0.03mm2) compared with Ldlr-/-WT (0.30 ± 0.04mm2, P < 0.05), although no differences in plaque composition were noted between groups. In addition, immunofluorescence analysis revealed increased splenic B and T cell areas independent of cell number. AID depletion directly inhibits atherosclerotic plaque formation.

The Platelet-Derived Growth Factor Pathway in Pulmonary Arterial Hypertension: Still an Interesting Target?

The lack of curative options for pulmonary arterial hypertension drives important research to understand the mechanisms underlying this devastating disease. Among the main identified pathways, the platelet-derived growth factor (PDGF) pathway was established to control vascular remodeling and anti-PDGF receptor (PDGFR) drugs were shown to reverse the disease in experimental models. Four different isoforms of PDGF are produced by various cell types in the lung. PDGFs control vascular cells migration, proliferation and survival through binding to their receptors PDGFRα and ß. They elicit multiple intracellular signaling pathways which have been particularly studied in pulmonary smooth muscle cells. Activation of the PDGF pathway has been demonstrated both in patients and in pulmonary hypertension (PH) experimental models. Tyrosine kinase inhibitors (TKI) are numerous but without real specificity and Imatinib, one of the most specific, resulted in beneficial effects. However, adverse events and treatment discontinuation discouraged to pursue this therapy. Novel therapeutic strategies are currently under experimental evaluation. For TKI, they include intratracheal drug administration, low dosage or nanoparticles delivery. Specific anti-PDGF and anti-PDGFR molecules can also be designed such as new TKI, soluble receptors, aptamers or oligonucleotides.

Platelet-Derived Growth Factor Receptor Type α Activation Drives Pulmonary Vascular Remodeling Via Progenitor Cell Proliferation and Induces Pulmonary Hypertension.

Background Platelet-derived growth factor is a major regulator of the vascular remodeling associated with pulmonary arterial hypertension. We previously showed that protein widely 1 (PW1+) vascular progenitor cells participate in early vessel neomuscularization during experimental pulmonary hypertension (PH) and we addressed the role of the platelet-derived growth factor receptor type α (PDGFRα) pathway in progenitor cell-dependent vascular remodeling and in PH development. Methods and Results Remodeled pulmonary arteries from patients with idiopathic pulmonary arterial hypertension showed an increased number of perivascular and vascular PW1+ cells expressing PDGFRα. PW1nLacZ reporter mice were used to follow the fate of pulmonary PW1+ progenitor cells in a model of chronic hypoxia-induced PH development. Under chronic hypoxia, PDGFRα inhibition prevented the increase in PW1+ progenitor cell proliferation and differentiation into vascular smooth muscle cells and reduced pulmonary vessel neomuscularization, but did not prevent an increased right ventricular systolic pressure or the development of right ventricular hypertrophy. Conversely, constitutive PDGFRα activation led to neomuscularization via PW1+ progenitor cell differentiation into new smooth muscle cells and to PH development in male mice without fibrosis. In vitro, PW1+ progenitor cell proliferation, but not differentiation, was dependent on PDGFRα activity. Conclusions These results demonstrate a major role of PDGFRα signaling in progenitor cell-dependent lung vessel neomuscularization and vascular remodeling contributing to PH development, including in idiopathic pulmonary arterial hypertension patients. Our findings suggest that PDGFRα blockers may offer a therapeutic add-on strategy to combine with current pulmonary arterial hypertension treatments to reduce vascular remodeling. Furthermore, our study highlights constitutive PDGFRα activation as a novel experimental PH model.

Design and development of Branched Poly(ß-aminoester) nanoparticles for Interleukin-10 gene delivery in a mouse model of atherosclerosis.

Atherosclerosis progression is a result of chronic and non-resolving inflammation, effective treatments for which still remain to be developed. We designed and developed branched poly(ß-amino ester) nanoparticles (NPs) containing plasmid DNA encoding IL-10, a potent anti-inflammatory cytokine to atherosclerosis. The NPs (NP-VHPK) are functionalized with a targeting peptide (VHPK) specific for VCAM-1, which is overexpressed by endothelial cells at sites of atherosclerotic plaque. The anionic coating affords NP-VHPK with significantly lower toxicity than uncoated NPs in both endothelial cells and red blood cells (RBCs). Following injection of NP-VHPK in ApoE-/- mice, Cy5-labelled IL-10 significantly accumulates in both whole aortas and aortic sinus sections containing plaque compared to injection with a non-targeted control. Furthermore, IL-10 gene delivery results in an attenuation of inflammation locally at the plaque site. NP-VHPK may thus have the potential to reduce the inflammatory component of atherosclerosis in a safe and effective manner. STATEMENT OF SIGNIFICANCE: Atherosclerosis is a chronic inflammatory disease that results in the formation of lipid-laden plaques within vascular walls. Although treatments using drugs and antibodies are now beginning to address the inflammation in atherosclerosis, neither is sufficient for long-term therapy. In this paper, we introduce a strategy to deliver genes encoding the anti-inflammatory protein interleukin-10 (IL-10) in vivo. We showed that Branched Poly(ß-aminoester) carrying the IL-10 gene are able to localize specifically at the plaque via surface-functionalized targeting moieties against inflamed VCAM-1 and/or ICAM-1 and to facilitate gene transcription by ECs to increase the local concentration of the IL-10 within the plaque. To date, there is no report involving non-viral nanotechnology to provide gene-based therapies for atherosclerosis.

Progenitor/Stem Cells in Vascular Remodeling during Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is characterized by an important occlusive vascular remodeling with the production of new endothelial cells, smooth muscle cells, myofibroblasts, and fibroblasts. Identifying the cellular processes leading to vascular proliferation and dysfunction is a major goal in order to decipher the mechanisms leading to PAH development. In addition to in situ proliferation of vascular cells, studies from the past 20 years have unveiled the role of circulating and resident vascular in pulmonary vascular remodeling. This review aims at summarizing the current knowledge on the different progenitor and stem cells that have been shown to participate in pulmonary vascular lesions and on the pathways regulating their recruitment during PAH. Finally, this review also addresses the therapeutic potential of circulating endothelial progenitor cells and mesenchymal stem cells.

FHL2 Is Essential for Spleen T Cell-Dependent B Cell Activation and Antibody Response.

Four-and-a-half LIM domain protein 2 (FHL2) is an adaptor molecule regulating various cellular processes, including signal transduction, transcription, and cell survival. Although involved in inflammation and immune responses, its role in the germinal center reaction and B cell maturation remains unknown. We found that FHL2-/- mouse spleens displayed enlarged follicles with more B cells. When a T cell-dependent immune response was elicited using SRBC, FHL2-/- germinal center area was enhanced 2-fold compared with wild type (WT), concomitant with expanded dark zones. Nevertheless, the SRBC-induced rise in spleen IgG1 expression, and plasma IgG1 levels observed in WT were absent in FHL2-/- mice, and circulating plasma cells were also reduced in FHL2-/- This could be explained by deficient upregulation of spleen activation-induced cytidine deaminase mRNA. Interestingly, FHL2-/- B cells successfully underwent class-switch recombination in vitro, and both activation-induced cytidine deaminase induction and IgG1 response to SRBC were equivalent in B cell-deficient µMT mice transplanted with WT or FHL2-/- bone marrow, suggesting that the defects observed in FHL2-/- mice were not B cell intrinsic. However, spleen lysates from FHL2-/- mice revealed a disturbed spleen microenvironment, with reduced CXCL12 and CXCL13 levels compared with WT. Our data suggest that spleen FHL2 expression is essential for a normal germinal center reaction and proper induction of class-switch recombination in response to a T cell-dependent Ag, leading to the emergence of Ab producing plasma cells. This could be due to the regulation of spleen cytokine production by FHL2.

Fibrogenic Potential of PW1/Peg3 Expressing Cardiac Stem Cells.

BACKGROUND: Pw1 gene expression is a marker of adult stem cells in a wide range of tissues. PW1-expressing cells are detected in the heart but are not well characterized. OBJECTIVES: The authors characterized cardiac PW1-expressing cells and their cell fate potentials in normal hearts and during cardiac remodeling following myocardial infarction (MI). METHODS: A human cardiac sample was obtained from a patient presenting with reduced left ventricular (LV) function following a recent MI. The authors used the PW1nLacZ+/- reporter mouse to identify, track, isolate, and characterize PW1-expressing cells in the LV myocardium in normal and ischemic conditions 7 days after complete ligature of the left anterior descending coronary artery. RESULTS: In both human and mouse ischemic hearts, PW1 expression was found in cells that were mainly located in the infarct and border zones. Isolated cardiac resident PW1+ cells form colonies and have the potential to differentiate into multiple cardiac and mesenchymal lineages, with preferential differentiation into fibroblast-like cells but not into cardiomyocytes. Lineage-tracing experiments revealed that PW1+ cells differentiated into fibroblasts post-MI. Although the expression of c-Kit and PW1 showed little overlap in normal hearts, a marked increase in cells coexpressing both markers was observed in ischemic hearts (0.1 ± 0.0% in control vs. 5.7 ± 1.2% in MI; p < 0.001). In contrast to the small proportion of c-Kit+/PW1- cells that showed cardiogenic potential, c-Kit+/PW1+ cells were fibrogenic. CONCLUSIONS: This study demonstrated the existence of a novel population of resident adult cardiac stem cells expressing PW1+ and their involvement in fibrotic remodeling after MI.

Resident PW1+ Progenitor Cells Participate in Vascular Remodeling During Pulmonary Arterial Hypertension.

RATIONALE: Pulmonary arterial hypertension is characterized by vascular remodeling and neomuscularization. PW1(+) progenitor cells can differentiate into smooth muscle cells (SMCs) in vitro. OBJECTIVE: To determine the role of pulmonary PW1(+) progenitor cells in vascular remodeling characteristic of pulmonary arterial hypertension. METHODS AND RESULTS: We investigated their contribution during chronic hypoxia-induced vascular remodeling in Pw1(nLacZ+/-) mouse expressing ß-galactosidase in PW1(+) cells and in differentiated cells derived from PW1(+) cells. PW1(+) progenitor cells are present in the perivascular zone in rodent and human control lungs. Using progenitor markers, 3 distinct myogenic PW1(+) cell populations were isolated from the mouse lung of which 2 were significantly increased after 4 days of chronic hypoxia. The number of proliferating pulmonary PW1(+) cells and the proportion of ß-gal(+) vascular SMC were increased, indicating a recruitment of PW1(+) cells and their differentiation into vascular SMC during early chronic hypoxia-induced neomuscularization. CXCR4 inhibition using AMD3100 prevented PW1(+) cells differentiation into SMC but did not inhibit their proliferation. Bone marrow transplantation experiments showed that the newly formed ß-gal(+) SMC were not derived from circulating bone marrow-derived PW1(+) progenitor cells, confirming a resident origin of the recruited PW1(+) cells. The number of pulmonary PW1(+) cells was also increased in rats after monocrotaline injection. In lung from pulmonary arterial hypertension patients, PW1-expressing cells were observed in large numbers in remodeled vascular structures. CONCLUSIONS: These results demonstrate the existence of a novel population of resident SMC progenitor cells expressing PW1 and participating in pulmonary hypertension-associated vascular remodeling.

Bone morphogenetic proteins protect pulmonary microvascular endothelial cells from apoptosis by upregulating α-B-crystallin.

OBJECTIVE: To investigate the role of bone morphogenetic proteins (BMPs) on α-B-crystallin (CRYAB) expression and its physiological consequences on endothelial cells (ECs). APPROACH AND RESULTS: We report that the gene encoding for the small heat shock protein, CRYAB, is a transcriptional target of the BMP signaling pathway. We demonstrate that CRYAB expression is upregulated strongly by BMPs in an EC line and in human lung microvascular ECs and human umbilical vein ECs. We show that BMP signals through the BMPR2-ALK1 pathway to upregulate CRYAB expression through a transcriptional indirect mechanism involving Id1. We observed that the known antiapoptotic effect of the BMPs is, in part, because of the upregulation of CRYAB expression in EC. We also show that cryab is downregulated in vivo, in a mouse model of pulmonary arterial hypertension induced by chronic hypoxia where the BMP pathway is downregulated. CONCLUSIONS: We demonstrate a cross-talk between BMPs and CRYAB and a major effect of this regulatory interaction on resistance to apoptosis.