Other research results showed that the HOTAIR expression level is upregulated in blood monocytes and serum exosomes of RA patients but downregulated in differentiated osteoclasts and rheumatoid synovial cells, and its overexpression can reduce the expression of matrix metalloproteinase 2 (MMP-2) and MMP-13 [29]. Here, MMP2 is linked to rheumatoid arthritis.