Bone Morphogenetic Proteins Protect Pulmonary Microvascular Endothelial Cells From Apoptosis by Upregulating α-B-Crystallin

Abstract

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. by interacting with proapoptotic proteins, or inhibiting caspase-3 activation. 10,12,15 In cardiomyocytes, it was shown that CRYAB silencing promoted cell death after exposure to H 2 O 2 , and that CRYAB has a protective role against apoptosis, by a mechanism involving translocation of CRYAB into mitochondria and by interacting with different proteins, including voltage-dependent anion channels and caspase-3. 16 Here, we show that BMPs induce CRYAB expression by a transcriptional, indirect molecular mechanism, which requires the BMPR2 and ALK1 receptors and the transcription factor Id1. BMPs protect EC from serum starvation and hypoxiainduced apoptosis and the protecting effect is, in part, because of a strong upregulation of the antiapoptotic protein CRYAB. cryab is downregulated in the lung of a mouse model of pulmonary hypertension induced by hypoxia, a condition in which the BMP signaling pathway has decreased activity. Materials and MethodsMaterials and Methods are available in the online-only Supplement. Results BMPs Upregulate CRYAB in Human Microvascular ECsMicroarray RNA profiling experiments were performed to identify BMP target genes in human microvascular EC-1 (HMEC-1) stimulated for 7 or 24 hours by 10 ng/mL of BMP4. Among the modulated genes, including ID1, ID2, and ID3, which were markedly upregulated (data not shown), we observed a strong upregulation of CRYAB expression by BMP4 at both 7 and 24 hours of stimulation.We confirmed, by real-time polymerase chain reaction (PCR), the upregulation of CRYAB expression in HMEC-1 treated by 10 ng/mL of BMP4 for 24, 48, and 72 hours (4.3±4.1, 8.6±0.7, and 7.5±1, respectively; Figure 1A). CRYAB mRNA was also increased by other members of the BMP growth factors family, BMP7 (fold increase at 4.8±0.9 at 24 hours, 4.8±1.8 at 48 hours, and 3.4±0.06 at 72 hours) and BMP9 (fold increase at 86.5±6.3 at 24 hours, 25.1±0.8 at 48 hours, and 15.1±1.5 at 72 hours), similar to BMP4 ( Figure 1A). In human lung microvascular ECs (HL...

αB-Crystallin Regulates Subretinal Fibrosis by Modulation of Epithelial-Mesenchymal Transition

“…Because BMP4 was induced in the CNV lesion after laser treatment in mice and up-regulates aB-crystallin in microvascular endothelial cells, 29 we investigated whether BMP4 up-regulates aB-crystallin in RPE cells. Expression levels of Figure 5 aB-crystallin (aB) silencing impairs nuclear translocation of SMAD4 mediated by its monotetraubiquitination.…”

“…29 To examine the expression changes of aB-crystallin and BMP4 in the development of subretinal fibrosis in mice, we measured aB-crystallin and BMP4 in the RPE-choroid complexes after laser injury of WT mice. 30 The concentration of aB-crystallin and BMP4 gradually increased, peaking at day 21 after laser ( Figure 2A).…”

Targeting BMP signalling in cardiovascular disease and anaemia

“…59,60 The indirect induction of alpha-crystallin B chain signalling via Id1 by BMP also contributes to the survival of pulmonary microvascular endothelial cells. 61 Id proteins also play an important effector role in the regulation of smooth muscle cell function by BMPs. Id1 and Id3 are potently regulated by BMP signalling in pulmonary arterial smooth muscle cells in vitro , 62 are jointly upregulated by hypoxia in pulmonary vascular smooth muscle in vivo , 63 and might play a complementary and partially redundant role in regulating cell cycling in vascular and other tissues.…”

The role of BMPs in endothelial cell function and dysfunction

“…The roles of BMP6 and BMP7 are becoming better understood, and their contributions to human diseases such as cerebral cavernous malformation (CCM) make these ligands crucial to study further (e.g., [4–6]). However, this review will focus on BMPs 2, 4, and 9 due to their welldefined roles in the vascular endothelium and recent studies that are addressing how these specific BMP signaling cascades affect endothelial dysfunction and human disease.…”