Role of Let-7b/Fzd4 Axis in Mitochondrial Biogenesis Through Wnt Signaling: In Neonatal and Adult Megakaryocytes

Background: Megakaryocytes (MKs), a rare population of bone marrow cells, are responsible for the production of platelets. Sick neonates are predisposed to developing thrombocytopenia (platelet count <150×109/L) and neonates are affected by several megakaryocyte disorders as compared to adults.

Hypothesis: MicroRNAs (miRNAs) have been shown to crucially involve in the regulation of stem-cell differentiation in normal as well as malignant hematopoiesis, but their role in regulation of biological differences between adult and neonatal megakaryopoiesis is unknown.

Methods: To study this, we cultured human cord blood (CB) and peripheral blood (PB) derived CD34 cells in the presence of thrombopoietin for 14days and collected cultures expressing>90% CD41 by flow cytometry and studied 88 miRNAs involved in stem cell development and differentiation. miRNA validation studies were performed in Dami cell line.

Results: Out of 88 miRNAs involved in stem cell development, let-7b was the only miRNA down regulated (∼10-fold) in neonates compared to adult-MKs. Let-7b has not been previously described in MKs, however reduced expression of let-7b was found in several human cancers, suggesting that it functions as a tumor suppressor. Our results showed the inhibitory effect of let-7b on wnt signaling pathway by regulating Fzd4 (frizzled family receptor 4) and thereby regulating proliferation as well as differentiation. Let-7b down regulation induced mitochondrial biogenesis and its markers PGC-1α and NRF1 during megakaryocyte development.

Conclusions: Our findings for the first time unveil the novel role of let-7b/Fzd4 axis through wnt signaling by regulating mitochondrial biogenesis during megakaryocyte development.