Abby Yovic

Introduction. The first step with any fracture is stabilizing and aligning the bone so that repair can start. Overall, fracture non-union rate is 4.93%. Recent research indicates MSCs provide options for cellular based therapies for bone repair due to their strong multipotentiality and regenerative properties. Maternally imprinted, lncRNA H19 located on chromosome 11p15.5² was corelated with osteogenic differentiation but mechanisms were not known. The competing endogenous RNA hypothesis states that all RNA transcripts, lncRNAs and protein coding RNAs, communicate with each other and compete for shared miRNAs. Altering the expression of lncRNAs can affect this balance and modify the cell differentiation pathways³. Methods. An experiment by Li et al. was conducted using stem cells from apical papilla tissue (SCAPs), extracted from the tips of growing roots. Recombinant lentivirus containing full length H19 and scramble control (NC); recombinant lentivirus targeting H19 (shH19-1, shH19-2) and targeting scramble control (shNC) were used to transfect the SCAPs. Transfected SCAPs were induced in the osteoblast differentiation medium. After 7 and 14 days, levels of H19, OCN, Runx2 and ALP, and calcium were measured. For the in vivo portion, SCAPs expressing H19 and controls were loaded on collagen scaffolds and implanted in the subcutaneous tissues of nude mice for 8 weeks. MSC with overexpressing H19 were injected subcutaneously into dorsal surface of nude mice; samples were collected after 8 weeks and analyzed¹. Results. H19 was upregulated on days 3 and 7, but proliferation itself was not. Higher levels of osteogenic biomarkers were present with H19 and lower with H19 knockout. Matrix mineralization and calcium levels were higher on days 3 and 14 in the presence of H19. More bone line structures, collagen deposits and osteocalcin were present when H19 is overexpressed. Target Scan software predicted matching of H19 and miRNA-141 and H19 was shown to act as a sponge for miRNA-141. Conclusions. This and other studies showed that H19 levels are elevated during later stages of MSC proliferation¹. Higher levels of ALP, calcium and matrix mineralization in the presence of H19 indicate that H19 promotes differentiation of SCAPs¹. Present experimental data suggests that miRNA inhibits SPAG9 expression (SPAG9 is a scaffold protein important in activation of p38 and JNK pathways which are in turn shown to be important for osteogenic differentiation) and upregulation of H19 has positive effects on the SCAPs differentiation through miRNA-141/SPAG9 pathway¹. These findings indicate that H19 can help in fracture repair process by affecting stem cell differentiation.

1. Li Z, Yan M, Yu Y, et al. LncRNA H19 promotes the committed differentiation of stem cells from apical papilla via miR-141/SPAG9 pathway. Cell Death Dis. 2019;10(2):130. Published 2019 Feb 12. doi:10.1038/s41419-019-1337-3
2. Zhou Q. P., Zhang F., Zhang J., Ma D. H19 promotes the proliferation of osteocytes by inhibiting p53 during fracture healing. European Review for Medical and Pharmacological Sciences. 2018;22(8):2226–2232. doi: 10.26355/eurrev_201804_14808.
3. Liang WC, Fu WM, Wang YB, et al. H19 activates Wnt signaling and promotes osteoblast differentiation by functioning as a competing endogenous RNA. Sci Rep. 2016;6:20121. Published 2016 Feb 8. doi:10.1038/srep20121