Identification of MRONJ-Specific Markers Using RNA-Mapping and Pathway Analysis

Objectives: Medication related osteonecrosis of the jaw (MRONJ) is a disorder characterized by loss of blood supply to the jaws and death to the bone. In our previously work, we created a rat model of MRONJ by two injections of 60ug/Kg zoledronic acid (ZA) via tail vein followed by extraction of a single first molar. We have shown in this model a decrease in the vasculature of the jaws and a delay in bone healing for rats beyond 4 weeks. The current study was designed to identify angiogenic factors from the jaws of our MRONJ model for use in tracking the decreased angiogenesis associated with the progression of MRONJ.
Methods: Using RT-PCR arrays containing 84 different gene sequences related to angiogenesis, we screened RNA isolated from the jaws of MRONJ, control, and ZA-treated rats 6 weeks after first molar extraction. Gene expression maps and pathway analyses for each treatment group were compared to controls.
Results: Our study demonstrates increased expression of 21 genes in rats treated with zoledronic acid (vs. controls). 16 of these genes (ACTB, B2M, COL4A3, CTGF, EFNA1, ENG, FGF1, FLT1, HIF1A, IL1B, LDHA, MDK, PGF, PLG, S1PR1, TNF) are expressed at control levels in the MRONJ group of rats 6 weeks after 1^st molar extraction. Increased expression of all 16 of these ZA-specific genes predicts activation of pathways of angiogenesis. 4 genes (IFNB1, RPLP1, THBS1, TIMP2) were expressed (relative to controls) in the MRONJ rats 6 weeks after 1^st molar extraction that did not show increased expression in rats in the ZA-treated rats without extraction. Increased expression of all 4 of these MRONJ-specific genes predicts inhibition of pathways of angiogenesis.
Conclusions: Our study identifies markers that predict the transition from early pro-angiogenic effects of zoledronic acid to late inhibition of angiogenesis with the development of MRONJ.