EphB4

Bone marrow vascular endothelial cells (BM ECs) regulate multiple myeloma (MM) pathogenesis. Identification of the mechanisms underlying this interaction could lead to the development of improved strategies for treating MM. Here, we performed a transcriptomic analysis of human ECs with high capacity to promote MM growth, revealing overexpression of the receptor tyrosine kinases, EPHB1 and EPHB4, in MM - supportive ECs. Expression of ephrin B2 (EFNB2), the binding partner for EPHB1 and EPHB4, was significantly increased in MM cells. Silencing EPHB1 or EPHB4 in ECs suppressed MM growth in co-culture. Similarly, loss of EFNB2 in MM cells blocked MM proliferation and survival in vitro, abrogated MM engraftment in immune-deficient mice, and increased MM sensitivity to chemotherapy. Administration of an EFNB2-targeted single chain variable fragment also suppressed MM growth in vivo. In contrast, overexpression of EFNB2 in MM cells increased STAT5 activation, increased MM cell survival and proliferation, and decreased MM sensitivity to chemotherapy. Conversely, expression of mutant EFNB2 lacking reverse signaling capacity in MM cells increased MM cell death and sensitivity to chemotherapy and abolished MM growth in vivo. Complementary analysis of MM patient data revealed that increased EFNB2 expression is associated with adverse-risk disease and decreased survival. This study suggests that EFNB2 reverse signaling controls MM pathogenesis and can be therapeutically targeted to improve MM outcomes.

Mesenchymal stem cells (MSCs) are known to facilitate angiogenesis and promote neo-vascularization via secretion of trophic factors. Here, we explored the molecular mechanism adopted by ADAMTS13 in modulating the expression of some key angiogenic markers in human umbilical cord-derived MSCs under serum-deprivation stress. Wharton's jelly MSCs (WJ-MSCs) were isolated from the perivascular region of human umbilical cords by explant culture. ADAMTS13 was upregulated at both mRNA and protein levels in WJ-MSCs under serum-deprivation stress. Correspondingly, some key angiogenic markers were also seen to be upregulated. By screening signaling pathways, p38 and JNK pathways were identified as negative and positive regulators for expression of ADAMTS13, and the angiogenic markers, respectively. Our results also indicated the Notch pathway and p53 as other probable partners modulating the expression of ADAMTS13 and the angiogenic markers. Knockdown of ADAMTS13 using siRNA led to reversal in the expression of these angiogenic markers. Further, ADAMTS13 was shown to act via the EphrinB2/EphB4 axis followed by ERK signaling to control expression of the angiogenic markers. Interestingly, stronger expression levels were noted for ADAMTS13, VEGF and PDGF under a more stringent nutrient stress condition. Thus, we highlight a novel role of ADAMTS13 in WJ-MSCs under nutrient stress condition.

Intracranial vascular malformations manifest on a continuum ranging from predominantly arterial to predominantly venous in pathology. Cerebral cavernous malformations (CCMs) are capillary malformations that exist at the midpoint of this continuum. The axon guidance factor Ephrin B2 and its receptor EphB4 are critical regulators of vasculogenesis in the developing central nervous system. Ephrin B2/EphB4 dysregulation has been implicated in the pathogenesis of arterial-derived arteriovenous malformations and vein-based vein of Galen malformations. Increasing evidence supports the hypothesis that aberrant Ephrin B2/EphB4 signaling may contribute to developing vascular malformations, but their role in CCMs remains largely uncharacterized. Evidence of Ephrin dysregulation in CCMs would be important to establish a common link in the pathogenic spectrum of EphrinB2/Ephb4 dysregulation. By studying patient-derived primary CCM endothelial cells (CCMECs), we established that CCMECs are functionally distinct from healthy endothelial cell controls; CCMECs demonstrated altered patterns of migration, motility, and impaired tube formation. In addition to the altered phenotype, the CCMECs also displayed an increased ratio of EphrinB2/EphB4 compared to the healthy endothelial control cells. Furthermore, whole exome sequencing identified mutations in both EphrinB2 and EphB4 in the CCMECs. These findings identify functional alterations in the EphrinB2/EphB4 ratio as a feature linking pathophysiology across the spectrum of arterial, capillary, and venous structural malformations in the central nervous system while revealing a putative therapeutic target.