Targeting neovascular pericytes in neurofibromatosis type 1

Apart from tumor-driven neovascularization, a less-appreciated consequence of neurofibromatosis type 1 (NF1) is the hyperproliferation of vascular mural cells (pericytes). This study aims at establishing a role for pericytes in NF1, and determining whether interference with the function of a key pericyte component (NG2 proteoglycan) inhibits NF1 tumor neovascularization. Neovascularization in NF1 was studied in Nf+/+(control), Nf1+/–, and Nf1–/–embryos at E-10, ischemia-induced retinal angiogenesis model in 24 eyes of Nf1+/–, Nf1+/+mice, and in malignant peripheral nerve sheath tumors (MPNSTs) derived from NF1 patients (ST88-14, NMS-2PC) orthotopically grown in nude mice (Crl: nu/nu). The anti-angiogenic effect of intracorneal polymer pellets containing anti-NG2 neutralizing antibody was quantified in the nude-mouse corneal angiogenesis model in which angiogenesis was induced by xenografting NMS-2PC tumor into the corneal stroma of 22 eyes. By using confocal microscopy, immunohistochemistry, and BrdU proliferation assay, the pericyte/endothelium ratios and proliferation rates were measured. Activated pericytes were present at the leading tip of the angiogenic sprouts. Pericytes showed continuous investment of endothelium in both NMS-2PC and ST88-14 MPNST tumor xenografts. Mean corneal angiogenesis induced by NMS-2PC tumor grafts in NG2-antibody treated eyes was 1.491 and 3.186 mm ² in isotype-matched non-immunoglobulin treated eyes (control) (P=0.0002). A total of 193.8 vascular nuclei (a measure of ischemia-induced retinal angiogenesis) was present in angiogenic retinal tufts in Nf1+/– mice compared to 89.23 in Nf1+/+ mice (control) (P < 0.0001). Mean pericyte/endothelium investment ratios were 1.015, 1.380, and 2.084 in control, Nf1+/–, and Nf1–/–embryos, respectively. Pericytes were 23% (control), 49% (Nf1+/–), and 69% (Nf1–/–) BrdU-positive. Endothelial cells from the same embryos were 29% (control), 47% (Nf1+/–), and 62% (Nf1–/–) BrdU-positive. Angiogenesis is accelerated in NF1 due to hyperproliferation of pericytes and endothelial cells. Mitotically activated NG2-positive pericytes, and endothelial cells may serve as potential therapeutic targets in NF1.     

Early Contribution of Pericytes to Angiogenic Sprouting and Tube Formation

Immunostaining with endothelial and pericyte markers was used to evaluate the cellular composition of angiogenic sprouts in several types of tumors and in the developing retina. Confocal microscopy revealed that, in addition to conventional endothelial tubes heavily invested by pericytes, all tissues contained small populations of endothelium-free pericyte tubes in which nerve/glial antigen 2 (NG2) positive, platelet-derived growth factor beta (PDGF beta ) receptor-positive perivascular cells formed the lumen of the microvessel. Perfusion of tumor-bearing mice with FITC-dextran, followed by immunohistochemical staining of tumor vasculature, demonstrated direct apposition of pericytes to FITC-dextran in the lumen, confirming functional connection of the pericyte tube to the circulation. Transplantation of prostate and mammary tumor fragments into NG2-null mice led to the formation of tumor microvasculature that was invariably NG2-negative, demonstrating that pericytes associated with tumor microvessels are derived from the host rather than from the conversion of tumor cells to a pericyte phenotype. The existence of pericyte tubes reflects the early participation of pericytes in the process of angiogenic sprouting. The ability to study these precocious contributions of pericytes to neovascularization depends heavily on the use of NG2 and PDGF beta -receptor as reliable early markers for activated pericytes.     

脑源性神经营养因子经NO/PKG/Sestrin2通路提高内皮细胞血管生成能力

目的研究脑源性神经营养因子(BDNF)对内皮细胞Sestrin2表达的影响及机制,并探讨其在血管新生中的作用。方法用100μg/L的BDNF分别处理人脐静脉内皮细胞(HUVEC)1 h、2 h、4 h、6 h、8 h,实时荧光定量PCR检测Sestrin2 mRNA水平,免疫荧光和Western blot检测Sestrin2蛋白表达。将HUVEC分为6组:对照组(Control组)、BDNF组(加BDNF 100μg/L)、BDNF+TrkB-Fc(1 mg/L)组、BDNF+KT-5823(500 nmol/L)组、BDNF+L-NAME(10~(-4) mol/L)组、BDNF+DMSO组,共干预4 h, Western blot检测Sestrin2蛋白表达。将HUVEC分为4组:对照组(Control组)、BDNF组(加BDNF 100μg/L)、BDNF+Sestrin2 siRNA组和BDNF+Control siRNA组,共干预6 h,细胞迁移实验和小管成形实验分别检测HUVEC迁移能力和血管生成能力。结果与0 h和1 h组比较,100μg/L BDNF分别干预HUVEC 2、4及6 h时段,Sestrin2 mRNA水平显著增高(P0.001),在2、4及8 h时段Sestrin2蛋白表达显著增高(P0.05);阻断NO/PKG通路可抑制BDNF诱导的Sestrin2表达上调(P0.001);抑制Sestrin2表达后,HUVEC迁移及小管形成能力较BDNF干预组显著降低(P0.01)。结论 BDNF通过NO/PKG通路促进内皮细胞表达Sestrin2,从而提高内皮细胞血管生成能力。     

The transformation of atrial fibroblasts into myofibroblasts is promoted by trimethylamine N-oxide via the Wnt3a/β-catenin signaling pathway

BackgroundAtrial fibrosis is an important pathophysiological mechanism in the development and maintenance of atrial fibrillation. Trimethylamine N-oxide (TMAO) is one of the most widely studied microbial metabolites involved in the promotion of cardiac fibrosis. TMAO promotes phenotypic transformation, proliferation, and migration and increases collagen secretion in cardiac fibroblasts. The Wnt/β-catenin pathway also plays a key role in the promotion of cardiac fibroblasts into myofibroblasts.MethodsThe expression of Alpha-smooth muscle actin (α-SMA) was determined to identify the formation of myofibroblasts. The effects of TMAO on the proliferation and migration of atrial fibroblasts were detected by cell counting kit 8, and transwell assays, respectively. Western blot and immunofluorescence were used to detect the activation of the β-catenin pathway by TMAO and the phenotypic transformation and collagen secretion of the atrial fibroblasts. Western blot and immunofluorescence assays were performed to detect the effects of exogenous Wnt3a and TMAO on the activation of β-catenin pathway and the phenotypic transformation of atrial fibroblasts.ResultsTMAO promoted the proliferation and migration of atrial fibroblasts. TMAO also promoted the phenotypic transformation, migration, and collagen secretion of the atrial fibroblasts by activating the β-catenin pathway. Exogenous Wnt3a and TMAO synergistically promoted the activation and phenotypic transformation of the β-catenin pathway in atrial fibroblasts.ConclusionsTMAO promotes the transformation of atrial fibroblasts into myofibroblasts by activating Wnt3a/β-catenin signaling pathway.