720 - TNFAIP8/TIPE2 Inactivation Modulates Extracellular Matrix Organization Gene Expression and Preserves Intervertebral Disc Structure in the Mouse

Back pain related to intervertebral disc (IVD) degeneration is a common clinical problem. Inflammatory cytokines and chemokines have been found in painful/degenerative human IVDs, and may account for some of the painful symptoms. The TNFAIP8 (tumor necrosis factor-α-induced protein 8) family comprises four highly homologous mammalian proteins, designated TNFAIP8 and TIPE1-3 (TNFAIP8-like 1-3, or TIPE1-3). The objective of this study is to determine the effects of Tnfaip8/Tipe2 gene deletion on the mouse IVD structure and global gene expression.

Design:

Morphological features of IVDs in the young adult Tnfaip8/Tipe2 double knockout (dKO) mice were compared with wild type (WT) mice on the same genetic background with Safranin’O and Hematoxylin & eosin staining. Histological scores were assessed by 2 independent readers. The whole RNA transcriptome of Tnfaip8/Tipe2 dKO mouse IVDs were compared with those of wild type mice by RNA sequencing (RNASeq).

Results:

The Tnfaip8/Tipe2 dKO mouse IVDs displayed higher levels of Safranin’O staining and better histological scores compared with WT (p< 0.01). A total of 349 genes differed in the IVDs of dKO and WT (P.adj < 0.01) mice. Gene ontology analysis for biological processes was performed, to give meaning to the 349 differentially expressed genes. Extracellular matrix organization and cell-substrate adhesion were the two most represented biological pathways. Protein-protein interaction network analysis revealed that fibronectin 1 and thrombospondin 1 had the highest number of protein-protein interactions.

Conclusions:

An unbiased bulk RNASeq approach was used to compare the transcriptomes of Tnfaip8/Tipe2-dKO and WT control mouse IVDs. Profound differences in the gene expression profiles were detected between the mutant and WT mouse IVDs. Importantly, Tnfaip8/Tipe2-dKO mouse discs retained more proteoglycan than the WT mice. Reduced expression locally in the disc may be beneficial in preventing tissue degeneration.