Loss of Quiescence in von Hippel-Lindau Hemangioblastomas is Associated with Erythropoietin Signaling

von Hippel-Lindau (VHL) patients develop multiple central nervous system hemangioblastomas (HB). Some HBs become symptomatic with exponential growth or cyst formation following long periods of quiescence. Understanding the factors underlying growth in hemangioblastoma may lead to better strategies to arrest or prevent tumor growth. In 5 VHL patients, we resected quiescent hemangioblastomas (Q-HB) that were en-route during surgical access to symptomatic hemangioblastomas (S-HB), for matched tumor analysis. Quantitative reverse transcriptase analysis demonstrated a 2-fold increase in EPO expression in all S-HB, while 4/5 showed either Hypoxia Inducible Factor-1α or 2α upregulation. Additionally, all S-HB had increased phosphorylated erythropoietin (EPO) receptor and phosphorylated STAT-5 relative to matched Q-HB, with increased phosphorylated JAK-2 largely confined to the stromal cells in clusters within the tumors. These findings suggest that Q-HB to S-HB conversion may be associated with an erythropoietin-signaling loop. Furthermore, we found that EPO is detectable in cyst fluid from S-HB (n = 14), while absent in CSF (n = 1). Additionally, S-HB presentation or S-HB resection does not result in discernible change in serum EPO or hemoglobin (n = 60). These observations suggest that the altered erythropoietin signaling is focal and suggests that studying modulation of erythropoietin receptor pathway may lead to strategies in preventing HB growth.