LRP1-dependent endocytic mechanism governs the signaling output of the bmp system in endothelial cells and in angiogenesis

Endothelial LRP1 transports amyloid-β(1-42) across the blood-brain barrier

According to the neurovascular hypothesis, impairment of low-density lipoprotein receptor-related protein-1 (LRP1) in brain capillaries of the blood-brain barrier (BBB) contributes to neurotoxic amyloid-β (Aβ) brain accumulation and drives Alzheimer's disease (AD) pathology. However, due to conflicting reports on the involvement of LRP1 in Aβ transport and the expression of LRP1 in brain endothelium, the role of LRP1 at the BBB is uncertain. As global Lrp1 deletion in mice is lethal, appropriate models to study the function of LRP1 are lacking. Moreover, the relevance of systemic Aβ clearance to AD pathology remains unclear, as no BBB-specific knockout models have been available. Here, we developed transgenic mouse strains that allow for tamoxifen-inducible deletion of Lrp1 specifically within brain endothelial cells (Slco1c1-CreER(T2) Lrp1(fl/fl) mice) and used these mice to accurately evaluate LRP1-mediated Aβ BBB clearance in vivo. Selective deletion of Lrp1 in the brain endothelium of C57BL/6 mice strongly reduced brain efflux of injected [125I] Aβ(1-42). Additionally, in the 5xFAD mouse model of AD, brain endothelial-specific Lrp1 deletion reduced plasma Aβ levels and elevated soluble brain Aβ, leading to aggravated spatial learning and memory deficits, thus emphasizing the importance of systemic Aβ elimination via the BBB. Together, our results suggest that receptor-mediated Aβ BBB clearance may be a potential target for treatment and prevention of Aβ brain accumulation in AD.

Bone morphogenetic proteins in tumour associated angiogenesis and implication in cancer therapies

Bone morphogenetic protein (BMP) belongs to transforming growth factor-β superfamily. To date, more than 20 BMPs have been identified in humans. BMPs play a critical role in embryonic and postnatal development, and also in maintaining homeostasis in different organs and tissues by regulating cell differentiation, proliferation, survival and motility. They play important roles in the development and progression of certain malignancies, including prostate cancer, breast cancer, lung cancer, etc. Recently, more evidence shows that BMPs are also involved in tumour associated angiogenesis. For example BMP can either directly regulate the functions of vascular endothelial cells or indirectly influence the angiogenesis via regulation of angiogenic factors, such as vascular endothelial growth factor (VEGF). Such crosstalk can also be reflected in the interaction with other angiogenic factors, like hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF). All these factors are involved in the orchestration of the angiogenic process during tumour development and progression. Review of the relevant studies will provide a comprehensive prospective on current understanding and shed light on the corresponding therapeutic opportunity.

Bone morphogenetic protein-4: a novel therapeutic target for pathological cardiac hypertrophy/heart failure

Bone morphogenetic protein-4 (BMP4) is a member of the bone morphogenetic protein family which plays a key role in the bone formation and embryonic development. In addition to these predominate and well-studied effects, the growing evidences highlight BMP4 as an important factor in cardiovascular diseases, such as hypertension, pulmonary hypertension and valve disease. Our recent works demonstrated that BMP4 mediated cardiac hypertrophy, apoptosis, fibrosis and ion channel remodeling in pathological cardiac hypertrophy. In this review, we discussed the role of BMP4 in pathological cardiac hypertrophy, as well as the recent advances about BMP4 in cardiovascular diseases closely related to pathological cardiac hypertrophy/heart failure. We put forward that BMP4 is a novel therapeutic target for pathological cardiac hypertrophy/heart failure.

The role of BMPs in endothelial cell function and dysfunction

The bone morphogenetic protein (BMP) family of proteins has a multitude of roles throughout the body. In embryonic development, BMPs promote endothelial specification and subsequent venous differentiation. The BMP pathway also plays important roles in the adult vascular endothelium, promoting angiogenesis and mediating shear and oxidative stress. The canonical BMP pathway functions through the Smad transcription factors; however, other intracellular signaling cascades can be activated, and receptor complexes beyond the traditional type I and type II receptors add additional layers of regulation. Dysregulated BMP signaling has been linked to vascular diseases including pulmonary hypertension and atherosclerosis. This review addresses recent advances in the roles of BMP signaling in the endothelium and how BMPs affect endothelial dysfunction and human disease.

Effects of siRNA targeting BMPR-II on the biological activities of human liver cancer cells and its mechanism

Background

Bone morphogenetic protein receptor II (BMPR-II) plays an important role in tumor’s invasion and proliferation. In this study, we observed the effects of small interfering RNA (siRNA) targeting bone morphogenetic protein receptor II (BMPR-II) on the biological activities of human liver cells and explore its mechanism.

Methods

The molecular sequences of three siRNA targeting BMPR-IIwere designed and synthesized. In this study, there were 6 groups including group I (normal control), group II (blank control), group III (negative control) and group IV-VI (BMPR-II-siRNA-a, siRNA-b and siRNA-c-transfected cells, respectively). The levels of mRNA and protein of BMPR-II were determined to select the best sequence for BMPR-II silence. After liver cancer cells were transfected with the best sequence, proliferation and invasion of transfected cells were assessed, and apoptosis and cell cycle were detected. The expressions of mitogen-activated protein kinases (MAPKs) signal pathway-related VEGF-C protein were observed after BMPR-II silence and BMPR-II silence combined with inhibiting MAPKs signal pathway, respectively.

Results

RT-PCR and Western blot indicated that BMPR-II expression was the highest in HepG2 among the three liver cancer lines (P < 0.01) and the lowest in group IV among the six groups (P < 0.01). MTT assay and transwell assay revealed that the numbers of cell growth and cell transmembrane were significantly lower in group IV than in control groups 48 h after cells were transfected (P < 0.05). Flow cytometer showed that apoptosis was the highest and cells were significantly blocked in S phase 48 h after cells were transfected in group IV (P < 0.01). Western blot indicated that the protein levels of p-P38 (P < 0.01) and vascular endothelial growth factor-C (VEGF-C) (P < 0.01) were significantly decreased after BMPR-II silence. The protein level of VEGF-C was significantly decreased in PD98059 + siRNA-BMPR-II-a and SB203580 + siRNA-BMPR-II-a groups (P < 0.01), especially in SB203580 + siRNA-BMPR-II-a group (P < 0.01).

Conclusions

siRNA targeting BMPR-IIcan markedly inhibit HepG2 proliferation and invasion, promote apoptosis and block HepG2 in S phase. Its mechanism may be that BMPR-II silence down-regulates VEGF-C expression through MAPK/P38 and MAPK/ERK1/2 pathways, especially MAPK/P38. This study provides a new targeted therapy for liver cancer.

BMPER-induced BMP signaling promotes coronary artery remodeling

The connection of the coronary vasculature to the aorta is one of the last essential steps of cardiac development. However, little is known about the signaling events that promote normal coronary artery formation. The bone morphogenetic protein (BMP) signaling pathway regulates multiple aspects of endothelial cell biology but has not been specifically implicated in coronary vascular development. BMP signaling is tightly regulated by numerous factors, including BMP-binding endothelial cell precursor-derived regulator (BMPER), which can both promote and repress BMP signaling activity. In the embryonic heart, BMPER expression is limited to the endothelial cells and the endothelial-derived cushions, suggesting that BMPER may play a role in coronary vascular development. Histological analysis of BMPER(-/-) embryos at early embryonic stages demonstrates that commencement of coronary plexus differentiation is normal and that endothelial apoptosis and cell proliferation are unaffected in BMPER(-/-) embryos compared with wild-type embryos. However, analysis between embryonic days 15.5-17.5 reveals that, in BMPER(-/-) embryos, coronary arteries are either atretic or connected distal to the semilunar valves. In vitro tubulogenesis assays indicate that isolated BMPER(-/-) endothelial cells have impaired tube formation and migratory ability compared with wild-type endothelial cells, suggesting that these defects may lead to the observed coronary artery anomalies seen in BMPER(-/-) embryos. Additionally, recombinant BMPER promotes wild-type ventricular endothelial migration in a dose-dependent manner, with a low concentration promoting and high concentrations inhibiting migration. Together, these results indicate that BMPER-regulated BMP signaling is critical for coronary plexus remodeling and normal coronary artery development.

Low-density lipoprotein receptor-related protein-1: role in the regulation of vascular integrity

Low-density lipoprotein receptor-related protein-1 (LRP1) is a large endocytic and signaling receptor that is widely expressed. In the liver, LRP1 plays an important role in regulating the plasma levels of blood coagulation factor VIII (fVIII) by mediating its uptake and subsequent degradation. fVIII is a key plasma protein that is deficient in hemophilia A and circulates in complex with von Willebrand factor. Because von Willebrand factor blocks binding of fVIII to LRP1, questions remain on the molecular mechanisms by which LRP1 removes fVIII from the circulation. LRP1 also regulates cell surface levels of tissue factor, a component of the extrinsic blood coagulation pathway. This occurs when tissue factor pathway inhibitor bridges the fVII/tissue factor complex to LRP1, resulting in rapid LRP1-mediated internalization and downregulation of coagulant activity. In the vasculature LRP1 also plays protective role from the development of aneurysms. Mice in which the lrp1 gene is selectively deleted in vascular smooth muscle cells develop a phenotype similar to the progression of aneurysm formation in human patient, revealing that these mice are ideal for investigating molecular mechanisms associated with aneurysm formation. Studies suggest that LRP1 protects against elastin fiber fragmentation by reducing excess protease activity in the vessel wall. These proteases include high-temperature requirement factor A1, matrix metalloproteinase 2, matrix metalloproteinase-9, and membrane associated type 1-matrix metalloproteinase. In addition, LRP1 regulates matrix deposition, in part, by modulating levels of connective tissue growth factor. Defining pathways modulated by LRP1 that lead to aneurysm formation and defining its role in thrombosis may allow for more effective intervention in patients.

LDL receptor-related protein-1: a regulator of inflammation in atherosclerosis, cancer, and injury to the nervous system

Low-density lipoprotein receptor-related protein-1 (LRP1) is an endocytic receptor for numerous proteins that are both structurally and functionally diverse. In some cell types, LRP1-mediated endocytosis is coupled to activation of cell signaling. LRP1 also regulates the composition of the plasma membrane and may, thereby, indirectly regulate the activity of other cell-signaling receptors. Given the scope of LRP1 ligands and its multifunctional nature, it is not surprising that numerous biological activities have been attributed to this receptor. LRP1 gene deletion is embryonic-lethal in mice. However, elegant studies using Cre-LoxP recombination have helped elucidate the function of LRP1 in mature normal and pathological tissues. One major theme that has emerged is the role of LRP1 as a regulator of inflammation. In this review, we will describe evidence for LRP1 as a regulator of inflammation in atherosclerosis, cancer, and injury to the nervous system.

Antagonism and synergy between extracellular BMP modulators Tsg and BMPER balance blood vessel formation

Growth and regeneration of blood vessels are crucial processes during embryonic development and in adult disease. Members of the bone morphogenetic protein (BMP) family are growth factors known to play a key role in vascular development. The BMP pathway is controlled by extracellular BMP modulators such as BMP endothelial cell precursor derived regulator (BMPER), which we reported previously acts proangiogenically on endothelial cells in a concentration-dependent manner. Here, we explore the function of other BMP modulators, especially Tsg, on endothelial cell behaviour and compare them to BMPER. In Matrigel assays, BMP modulators chordin and noggin had no stimulatory effect; however, gremlin and Tsg enhanced human umbilical vein endothelial cell (HUVEC) sprouting. As the activation dynamics of Tsg were similar to those of BMPER, we further investigated the proangiogenic effect of Tsg on endothelial cells. Tsg enhanced endothelial cell ingrowth in the mouse Matrigel plug assay as well as HUVEC sprouting, migration and proliferation in vitro, dependent on Akt, Erk and Smad signalling pathway activation in a concentration-dependent manner. Surprisingly, silencing of Tsg also increased HUVEC sprouting, migration and proliferation, which is again associated with Akt, Erk and Smad signalling pathway activation. Furthermore, we reveal that Tsg and BMPER interfere with each other to enhance proangiogenic events. However, in vivo the presence of Tsg as well as of BMPER is mandatory for regular development of the zebrafish vasculature. Taken together, our results suggest that BMPER and Tsg maintain a fine-tuned equilibrium that controls BMP pathway activity and is necessary for vascular cell homeostasis.