Interleukin-4 released from human gingival fibroblasts reduces osteoclastogenesis

Area of Science:

• Periodontal tissue biology
• Immunology
• Cell biology

Background:

• Human gingival epithelium is the primary defense against oral bacteria.
• Maintaining healthy gingival tissue is vital for preventing inflammatory periodontal diseases such as gingivitis and periodontitis.

Purpose of the Study:

• To investigate the role of interleukin-4 (IL-4) produced by human gingival fibroblasts (hGF) in regulating osteoclast activation.

Main Methods:

• Human gingival fibroblasts (hGF) were cultured, and their conditioned medium (hGF-CM) was analyzed for mRNA expression of osteoclastogenesis mediators.
• Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect IL-4 and osteoprotegerin (OPG) mRNA.
• The inhibitory effects of hGF-CM, recombinant human IL-4 (rhIL-4), and recombinant human OPG (rhOPG) on osteoclast differentiation in RAW264 macrophages were assessed using tartrate-resistant acid phosphatase (TRAP) staining and activity assays.
• Neutralizing antibodies against IL-4 were used to confirm IL-4's suppressive role.

Main Results:

• hGF-CM significantly reduced TRAP-positive staining and osteoclast activity in a dose-dependent manner.
• IL-4 and OPG mRNA were detected in hGF-CM, while IL-10, IL-27, and IL-33 were not.
• Both rhIL-4 and rhOPG inhibited osteoclast differentiation and activity in RAW264 cells.
• Neutralization of IL-4 diminished the inhibitory effect of hGF-CM on osteoclastogenesis.

Conclusions:

• Human gingival fibroblasts (hGF) secrete suppressive mediators, notably IL-4 and OPG, which inhibit osteoclastogenesis.
• Both OPG and IL-4 contribute to the differential inhibition of osteoclast formation observed in hGF-conditioned medium.