Sialylation, an important post-translational modification, plays a key role in processes such as cell recognition and signal transduction. This study aims to explore the role of α-2,3 sialylation in osteogenic and chondrogenic differentiation, further elucidate its impact on bone development by regulating extracellular matrix (ECM) homeostasis, and provide novel theoretical basis and potential intervention targets for disorders of skeletal development.

The expression profiles of sialyltransferase family genes in osteogenic and chondrogenic differentiation were analyzed using public datasets GSE109503 (chondrogenic differentiation) and GSE113253 (osteogenic differentiation). In vitro differentiation experiments were conducted using MC3T3-E1 osteoblast and ATDC5 cells, and qRT-PCR was performed to screen for core differentially expressed genes (DEGs) in the sialyltransferase family (screening threshold |Log₂FC|>1, P<0.05). Stable α-2,3-type sialylation-deficient MC3T3-E1 and ATDC5 cells were constructed using lentiviral vectors, followed by osteogenic or chondrogenic induction for 7 and 14 d. Differentiation capacity was evaluated by ALP staining, Alizarin Red S staining, and Alcian blue staining. The expression of osteogenic marker genes (Col1a1, Sp7) and chondrogenic marker gene (Col2a1) was detected by qRT-PCR and Western blotting. Transcriptome sequencing was performed on α-2,3 sialylation-deficient MC3T3-E1 cells (osteogenic induction for 7 d) and ATDC5 cells (chondrogenic induction for 7 d), and biological functions of DEGs were analyzed with GO and KEGG enrichment analyses. For in vivo experiments, newborn C57BL/6 mice (half male and half female, body weight 1.0 to 1.5 g, on the day of birth) were randomly divided into 2 groups: an sialidase-treated group (intraperitoneally injected with sialidase, 0.2 U/dose, every other day for 4 weeks), and a control group (same volume of normal saline), with 6 animals in each group. Micro-CT scanning was conducted to analyze the bone microstructure parameters of the femur.

Public dataset analysis revealed that only St3gal1 was significantly upregulated during both osteogenic and chondrogenic differentiation (|Log₂FC| >1, P<0.05). The in vitro cell differentiation model confirmed that St3gal1was significantly upregulated in both differentiation processes (P<0.000 1). Consistent with the public dataset transcriptome sequencing results, this demonstrated that St3gal1-mediated α-2,3-type sialylation accompanies the progression of osteogenic and chondrogenic differentiation. Following disruption of α-2,3 sialylation, ALP staining and Alizarin Red S staining in MC3T3-E1 cells were significantly attenuated, along with the mRNA expression levels of Col1a1and Sp7reduced to 60.7% (P<0.000 1) and 49% (P<0.000 1) of the control group, respectively, and corresponding protein levels decreasing to 61.5% (P=0.000 2) and 56.1% (P=0.000 3), respectively. In ATDC5 cells, Alcian Blue staining was markedly diminished, and CollagenⅡ protein expression was reduced to 43.1% of the control group (P<0.000 1). Transcriptomic sequencing results demonstrated that DEGs in both cell types were significantly enriched to ECM structure, and molecular functions were associated with ECM structural constituent. Pathway enrichment analyses revealed that DEGs were significantly enriched in ECM-receptor interaction and related signaling pathways (|Log₂FC|>1, FDR<0.05), suggesting that sialylation may regulate osteogenic and chondrogenic differentiation through multiple pathways, including ECM homeostasis, thereby contributing to bone development. In vivo experiments confirmed that, the sialidase-treated group exhibited reductions in femoral bone mineral density (decreased by 0.078 g/cm³, P<0.000 1), trabecular bone volume fraction (decreased by 5.512%, P<0.000 1), cortical thickness (decreased by 0.012 mm, P=0.001 1), trabecular number (decreased by 1.39/mm, P<0.000 1), and trabecular thickness (decreased by 0.002 3 mm, P=0.026 7), and an increase in trabecular separation (increased by 0.35 mm, P<0.000 1) when compared with the control group, indicating impaired skeletal development.

α-2,3 Sialylation positively regulates osteogenic and chondrogenic differentiation through modulating ECM homeostasis and plays an essential role in skeletal development. Sialylation within the bone microenvironment may serve as a potential intervention target for skeletal dysplasia disorders.