Fracture healing in a polytrauma rat model is influenced by mtDNA:cGAS complex mediated pro‐inflammation

Abstract

Purpose The mitochondrial DNA (mtDNA) activated cyclic guanosine monophosphate–adenosine monophosphate synthase—stimulator of interferon genes (cGAS-STING) signaling pathway is a key player in mediating immune responses in autoimmune disorders and cancer. However, its role in severe trauma associated fracture healing is unknown. This study investigated if the cGAS-STING signaling pathway contributes to delayed bone healing in polytrauma (PT) fractures. Methods For preliminary analyses, therapeutic dosage of RU.521 (cGAS inhibitor) (n = 2) was determined in C57BL/6 J mice by mass spectrometry, and IFNβ expression levels in serum and bronchioalveolar fluid (BALF) at 6 and 24 h (h) in RU.521/vehicle + mtDNA injected mice (n = 3/treatment and time point) was measured by ELISA. In the main study, plasma mtDNA was quantified by qPCR in a clinically relevant delayed fracture healing PT rat model with burn injury, blunt trauma, and a femoral fracture at 3 h post-trauma (hpt). Next, PT rats received either RU.521 (12 mg/kg in povidone; n = 8) or vehicle (povidone only; n = 5) immediately after injury and were followed up for 5 weeks post-trauma to assess bone regeneration by radiography and histology. Results IFNβ levels were significantly decreased only at 24 h in BALF of RU.521 treated mice. At 3hpt mtDNA was significantly elevated in PT rats compared to rats without injury. When treated with RU.521, PT rats showed improvement in bone healing compared to vehicle control PT rats. Conclusions These data reveal that the cGAS-STING signaling pathway influences trauma-induced delayed bone healing. However, further evaluation of this pathway at the cellular and molecular levels to augment PT associated detrimental effects is needed.

STING-Pathway Inhibiting Nanoparticles (SPINs) as a Platform for Treatment of Inflammatory Diseases

“…Both of these inhibitors have improved outcomes in an expanding diversity of preclinical rodent models of diseases. RU.521 has been used to improve disease outcomes in rodent models of neuroinflammation caused by subarachnoid hemorrhage and cerebral venous sinus thrombosis, colitis, sepsis-induced organ injury, , acetaminophen-induced liver injury, acute lung injury, hypertensive heart injury, ischemic injury in the lung and neonatal brain, femoral fracture healing, and aging-related endothelial dysfunction . Additionally, administration of H-151 has improved outcomes in rodent models of acute kidney injury (AKI), renal fibrosis, amyotrophic lateral sclerosis (ALS), sepsis-induced organ injury, , psoriasis, ischemia-reperfusion injury in the intestine, myocardial infarction, LPS-induced acute lung injury, , Alzheimer’s, and neuropathic pain resulting from chronic constriction injury .…”