The E74-like factor 3 (ELF3) is a central mediator of cartilage degradation in a surgically-induced osteoarthritis model in mice

Purpose: The transcription factor E74-like factor 3 (ELF3) plays a central role in mediating aberrant stress- and inflammatory signals in osteoarthritic (OA) chondrocytes. ELF3 mRNA levels are elevated in OA chondrocytes and contribute to the IL1β-induced expression of matrix metalloproteinase 13 (Mmp13), Nos2, and Ptgs2/Cox2 in vitro, indicating a pivotal role of ELF3 in cartilage degradation. Here, we aimed to investigate the contribution of gain- and loss-of-function of Elf3 to cartilage degradation in vivo. Methods: CARTILAGE-SPECIFIC ELF3 KNOCKOUTS: We generated Col2a1Cre-driven cartilage-specific Elf3 knockout (KO) mice. We subjected 12-weeks-old male KO or control Elf3f/f (WT) littermates to the destabilization of the medial meniscus (DMM) surgical model of OA. TET-OFF INDUCIBLE ELF3-OVEREXPRESSING MICE: We generated TRE-Elf3:Comp-tTA (Tg) mice by crossing transgenic mice that express Elf3 under the control of the tetracycline-responsive element (TRE) with Comp-tTA mice expressing tTA under the control of the Cartilage Oligomeric Matrix Protein (Comp) promoter. Inducible, post-natal overexpression of Elf3 was assessed at 3, 6 and 9 months of age in Tg or Ctrl (Comp-tTA) mice. The contribution of Elf3 overexpression to spontaneously-induced OA was assessed in 6 and 9 month-old Tg and Ctrl mice. The contribution of Elf3 to the DMM-induced cartilage degradation was evaluated using 6 months-old Ctrl and Tg mice at 8-wks post-DMM surgery. SURGICAL MODEL OF OA: 12-weeks-old (WT or KO) and 6 months-old (Tg or Ctrl) male mice were subjected to the DMM surgical model of OA. DMM was performed on the right knees, while the left knees were left as unoperated controls. At 4, 8 and 12-wks (WT or KO mice) or at 8-wks (Tg and Ctrl mice) post-DMM, knees were processed for histological assessment of OA, conducted on Safranin-O/Fast green-stained serial coronal sections following OARSI guidelines. RTqPCR ANALYSIS: Total RNA was isolated from the articular cartilage of control and DMM-operated WT and KO mice at 8-wks post-DMM. The total RNA was reverse-transcribed and amplified using SYBR Green I-based qPCR and specific primers for Elf3, Mmp13, Nos2, and Ptgs2. Data were normalized using Eef1a1, Gapdh and Hprt1 as housekeeping genes. Results: Histological assessment of OA severity showed attenuation of cartilage loss at 8 and 12 wks post-DMM surgery in KO mice compared to WT animals. We observed reduced MMP13-mediated collagenase activity, and decreased expression of Mmp13, Nos2, and Ptgs2/Cox2, assessed by RTqPCR analysis, in KO mice at 8-wks post-DMM. Importantly, while the TRE-Elf3:Comp-tTA (Tg) mice showed a trend towards increased cartilage damage at 6 and 9 months of age, the DMM-operated Tg mice exhibit significantly increased cartilage loss compared to Ctrl counterparts, suggesting that biomechanical challenge may be required to fully activate Elf3. Conclusions: Here, we provide evidence that Elf3 is a central contributing factor for cartilage degradation in vivo, in OA disease. Cartilage-specific Elf3 deficiency protects against surgically-induced OA and Elf3 overexpression results in exacerbated cartilage degradation in mice subjected to the DMM surgery. Cartilage-specific Elf3 knockout mice have decreased MMP13/collagenase activity and decreased expression of several Elf3 target genes, including Mmp13. Our results are consistent with previous reports in vitro; showing reduced IL-1β-driven Mmp13 expression in murine Elf3-/- chondrocytes and in human OA primary chondrocytes with siRNA-mediated ELF3 knockdown. Together, our in vivo an in vitro data represent strong evidence of a central role of Elf3 in the pathogenesis of OA, by controlling Mmp13-mediated collagen degradation. Thus, a better understanding of the mechanisms of action of Elf3 in chondrocytes will lead to the identification and development of targeted therapies for OA.