Poster Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

RUNX1 PROMOTES INTERVERTEBRAL DISC AGING (#38)

Takanori Fukunaga 1 2 , Changli Zhang 1 2 , Sreekala Shenoy 1 2 , Martha Elena Diaz-Hernandez 1 2 , Hicham Drissi 1 2
  1. Emory University, Atlanta, GA, United States
  2. The Atlanta VA Health Care System, Atlanta, GA, United States

INTRODUCTION: Aging is one of the most important risk factors contributing to chronic intervertebral disc degeneration (IDD), however a comprehensive understanding of the disc during aging remains lacking. Prevailing consensus suggests that depletion of nucleus pulposus (NP) cells and remodeling of the extracellular matrix (ECM) initiate the development of IDD1. Even though these changes are being described in aging, the mechanism remains poorly defined. Runx1 is a well-known transcription factor contributing to hematopoiesis, chondrogenesis and bone formation2. However, the role of Runx1 in IDD has been rarely elucidated. Our previous transcriptomics analysis identified Runx1 as a master regulator of in the pathogenesis of IDD3. This study aims to deepen our understanding Runx1 function during IDD.

 

METHODS: All animal research was subject to Institutional IACUC approval. To achieve conditional overexpression of Runx1 in NP cells, we crossed Rosa26-LSL-Runx1Tg/+; with the Krt19-CreERT NP-specific transgenic mice.  To induce CreERT activity, intraperitoneal injections of tamoxifen was performed at 4 weeks of age in (Rosa26-LSL-Runx1Tg/+) and (Krt19-CreERT; Rosa26-LSL-Runx1Tg/+) mice. Histological and molecular changes in IVD were assessment at 5, 7 and 10 months. Total RNA and protein were extracted to evaluated Runx1 expression levels by rt-PCR and western blot analyses. X-rays and histological analyses of lumbar IVD sections were at performed at L4/5 spine levels. Disc height, histology and antibody staining were used to compare control and overexpression animals.

 

RESULTS: Krt19-CreERT; Rosa26-LSL-Runx1Tg/+  mice showed increased in Runx1 gene expression and protein levels (Fig. 1). Analyses of the IVD height showed no significant differences between control and overexpressing mice at 5 months, however, a trend in reduction of disc height in Runx1 overexpression mice occurred at 7 and 10 months age (Fig. 2). Histological findings revealed that Runx1 overexpression led to changes in cell number, cell and NP matrix organization starting at 5 months. NP cells were scattered and NP matrix disorganization was observed at 7 months. At 10 months, NP cells started to appear as chondrocyte-like cells and the demarcation between the NP and AF became unclear (Fig. 3). Moreover, the type 2 collagen expression has enhanced in the NP matrix and AF in Runx1 overexpression (Fig. 4). Runx1 overexpression mice showed  acceleration of degenerative changes when comparing with control mice.

 

DISCUSSION: This study demonstrated that Runx1 overexpression accelerated aging-induced IDD. Previous literature showed that natural mice aging-induced degeneration has occurred at 14 months4, however, Runx1 overexpression induced IDD even at 5 months. Besides, the histological changes such as chondrocyte-like cells and matrix remodeling in the NP is an early step involved in the aging process, the exploration of this processes will likely pave the way for innovative approaches in the future.

 

Acknowledgement: Funded by NIH/NIAMS R01, AR076427 and the Department of Orthopaedics at Emory University School of Medicine.

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  1. Wang X, Tan Y, Liu F, et al. Pharmacological network analysis of the functions and mechanism of kaempferol from Du Zhong in intervertebral disc degeneration (IDD). J Orthop Translat. 2023;39:135-146.
  2. Liu Y, Huang C, Bai M, Pi C, Zhang D, Xie J. The roles of Runx1 in skeletal development and osteoarthritis: A concise review. Heliyon. 2022;8(12):e12656.
  3. Khan NM, Diaz-Hernandez ME, Presciutti SM, Drissi H. Network Analysis Identifies Gene Regulatory Network Indicating the Role of RUNX1 in Human Intervertebral Disc Degeneration. Genes. 2020;11(7):771.
  4. Ohnishi T, Sudo H, Tsujimoto T, Iwasaki N. Age-related spontaneous lumbar intervertebral disc degeneration in a mouse model. J Orthop Res. 2018;36(1):224-232.