Inhibition Of HIF1α Signaling Prevents Heterotopic Ossification Via Suppressing The Early Abnormal Immune Response In Injury Induced,BMP Dependent Mouse Model

Background:Heterotopic ossification(HO),acquired or hereditary,is characterized by ossification in the soft tissues.Fibrodysplasia ossificans progressiva(FOP),a hereditary and life-threatening HO,is caused by gain-of-function mutations of ACVR1.Acquired HO is normally a serious complication of trauma,such as burn,spinal cord injury and traumatic brain injury.Mechanistically,recent studies suggested that tissue-specific mesenchymal stem cells(MSCs),which have tremendous potential in tissue engineering,were likely the cellular origin of HO.MSC niche(microenvironment),composed of MSCs,supportive cells and supportive molecules,regulates HO initiation and propagation.More specifically,immune cells(T/B cells and master cells),as the supportive cells,are thought to participate in abnormal immune response(AIR)in response to traumatic injures,and set up a pre-condition for HO.Consistently,anti-inflammatory drugs were used in the prevention of HO.However,it is still largely unknown how AIR regulates HO.In addition,investigators also indicated that HIF1α and Activin A signaling might be involved in pathogenesis of HO.In this study,we first examined the peripheral WBC number in the HO mice and found enhanced immune response in the early stages of HO.In contrast,in the late stage,immune response was suppressed.This data provided the direct evidence of AIR in HO.We then tested whether inhibition of HIF1α with PX-478 prevented the HO.Overall,our data showed novel insights of molecular and cellular mechanisms that could serve as potential targets of prevention and treatment of HO.Research methods:1.Breed the Nse-BMP4,the transgenic mouse model of HO.2.Treat the Nse-BMP4 mice with PX-478 in the context of injury induced HO and use the X-ray images to determine the HO.Nse-BMP4 and wildtype(WT)mice injected with PBS were considered as a control.3.Target tissues,including peripheral blood and injured limbs were harvested for further analysis.4.IHC was used to examine the local immune cells and ELISA was used to measure the Activin A.Research results:1.Abnormal immune response(AIR)was observed.2.PX-478 effectively suppressed HO formation.3.PX-478 inhibited WBC number in the context of injury induced immune response,in both Nse-BMP4 and Wildtype mice.4.PX-478 suppressed the early expression of HIF1α and Activin A.Conclusions:1.Abnormal immune response(AIR)promotes the formation of HO.2.Inhibition of HIF1α can effectively modulate abnormal immune response.3.Activin A signaling might play a role in HO.