Progranulin promotes osteogenic differentiation of human periodontal ligament stem cells via tumor necrosis factor receptors to inhibit TNF-α sensitized NF-kB and activate ERK/JNK signaling

Objective To investigate the molecular mechanism of Progranulin (PGRN) in promoting osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) in inflammatory environment. Background Progranulin is an antagonist of tumor necrosis factor (TNF) receptors (TNFRs) and is known to promote inflammatory periodontal bone defect regeneration. Methods TNFR1- and TNFR2-silenced hPDLSCs designed as hPDLSCs-sh-TNFR1 and hPDLSCs-sh-TNFR2 were cultured with osteoinductive medium containing TNF-alpha and (or) PGRN. Immunofluorescence, quantitative real-time PCR, and western blot were used to, respectively, detect expressions of TNFR1\TNFR2 and osteogenic differentiation markers as well as phosphorylation level in NF-kappa B\MAPK-related pathways. Results Immunofluorescence and real-time PCR showed that TNFR1 and TNFR2 positively expressed in hPDLSCs. TNF-alpha stimulation could significantly decrease the expressions of ALP and RUNX2 in hPDLSCs, whereas PGRN treatment could significantly enhance their expressions, and reverse TNF-alpha-mediated expression suppression of ALP and RUNX2 in hPDLSCs. In hPDLSCs-sh-TNFR1, TNF-alpha mediated osteogenic inhibition decreased, but both TNF-alpha + PGRN and alone PGRN significantly promoted expression of ALP and RUNX2. PGRN significantly enhanced expression of P-ERK1/2 and P-JNK, while corresponding inhibitors eliminated PGRN-stimulated osteogenic differentiation. In hPDLSCs-sh-TNFR2, no significant difference existed in osteogenic markers and P-JNK expression between the PGRN group and the control group. However, PGRN still activated P-ERK1/2 expression. Besides, PGRN antagonized TNF-alpha-enhanced NF-kappa B P65 expression. Conclusion Progranulin promotes osteogenic differentiation of hPDLSCs via TNFR1 to inhibit TNF-alpha-sensitized NF-kappa B and via TNFR2 to activate JNK signaling. The mechanism by which PGRN activates ERK signaling remains to be explored.