Nucleotides modulate synoviocyte proliferation and osteoclast differentiation in macrophages with potential implications for rheumatoid arthritis

P2 receptors are nucleotide-activated receptors involved in inflammation, cell proliferation osteoblastogenesis, osteoclastogenesis and their function. They can be potential role players in the pathophysiology of rheumatoid arthritis (RA). Our analysis of gene expression datasets of synovial tissue biopsy from the GEO database shows changes in the expression levels of P2 receptors. HIG-82, a synovial fibroblast cell line and RAW 264.7, a macrophage cell line are good in vitro models to study RA. Nucleotide addition experiments showed UDP Glucose significantly increased the proliferation of synovial fibroblasts (HIG-82). Similarly, nucleotides such as Adenosine tri-phosphate (ATP), Adenosine di-phosphate (ADP), Uridine tri-phosphate (UTP), Uridine di-phosphate (UDP) and Uridine diphosphoglucose (UDPG) induced elevated reactive oxygen species (ROS) and tartrate Resistant Acid Phosphatase (TRAP) activity in RAW264.7 cells. The ADP-induced TRAP could be inhibited by clopidogrel a P2Y 12 inhibitor. ATP, ADP, UTP, UDP and UDPG also induced osteoclastogenesis as evident from fused multinucleate cells and expression of osteoclast markers (TRAP, Cathepsin K [CTSK]) as determined by Q-PCR. Apyrase (APY) a nucleotidase and an enzyme that is used to modulate extracellular nucleotide concentration is sufficient to induce osteoclastogenesis. Taken together our results show that nucleotides modulate synoviocyte proliferation and macrophage differentiation into osteoclast and play an important role in RA. Nucleotide receptors might be potential therapeutic targets in RA.