30Germ cell 1 spermatogonial (GC-1spg) cells are multipotent progenitor cells. We 31 previously confirmed that bone morphogenetic protein (BMP) 9 is among the most 32 osteogenic BMPs. However, whether GC-1spg cells are driven toward osteogenic 33 differentiation under proper stimuli is uncertain. Additionally, the molecular 34 mechanism of BMP9 remains unclear. In the present study, we aimed to determine 35 whether BMP9 can induce osteogenic differentiation of GC-1spg cells. Recombinant 36 adenoviruses were generated by the AdEasy system to regulate the BMP9 expression in 37 GC-1spg cells. We identified osteogenic markers by real-time PCR and staining 38 techniques in vitro. Ectopic ossification assays and histological analysis were also 39 performed to verify the in vivo activity of BMP9. Finally, potential signaling pathways 40 of BMP9 were assessed by transcriptome sequencing and KEGG enrichment analysis.
41Using recombinant adenoviruses, we demonstrate that BMP9 upregulates osteogenic 42 markers including Runx2, osteocalcin, osteopontin, and Sox9. BMP9 also activates 43 alkaline phosphatase activity and calcium deposition in GC-1spg cells. In vivo results
44show that BMP9 overexpression in GC-1spg cells promotes ectopic bone formation and 45 chondrogenesis. In addition, RNA-sequencing and KEGG pathway analysis 3 46 demonstrate that several signaling pathways are involved in BMP9-mediated 47 osteogenesis. GC-1spg cells not only maintain spermatogenesis but also retain the 48 ability to form bone tissue. Therefore, BMP9 activity in GC-1spg cells may help 49 identify signaling pathways implicated in bone formation and could be of use in 50 regenerative medicine. 51 Keywords: Bone morphogenetic protein 9, RNA-seq, KEGG pathway analysis, 52 recombinant adenovirus, chondrogenesis 53 Introduction 54 Germ cell 1 spermatogonial (GC-1spg) cells are mouse spermatogonia that are 55 immortalized by the SV40 large T antigen [1]. These cells can differentiate into diverse cell 56 types or undergo self-renewal, depending on different factors [2,3,4]. GC-1spg cells are 57 largely involved in spermatogenesis and have mesenchymal stem cell (MSC) differentiation 58 potential [5,6,7,8]. In other words, GC-1spg cells can differentiate into different cell types, 59including those of the osteogenic, chondrogenic, or adipogenic lineages [9,10,11,12].
60However, several molecular events [13,14] and factors are involved in osteogenic 61 differentiation of MSCs. Importantly, bone morphogenetic proteins (BMPs) are essential for 62 this process [15,16,17]. 63 BMPs, members of the TGF-β superfamily, are required for bone formation, stem cell 64 differentiation, and male reproduction [15,16,18,19,20]. Thus far, more than 15 different 65 BMPs have been identified. Our previous work showed that BMP9 is the most osteogenic 66 BMP [21,22,23,24]. BMP9, also known as growth differentiation factor 2 (GDF-2)[25], was 67 originally isolated from the fetal mouse liver [25,26]. Bone formation involves BMP9 acting 68 through the Notch signaling ...