The Role Of MFN1/2 In The Maintenance Of Intestinal Homeostasis

The intestinal epithelium is a multicellular interface in close proximity to a dense microbial milieu that is completely renewed every 3–5 days,composed of upturned villus and depressed-down crypts.Intestinal stem cells(crypt base columnar cells(CBCs))continuously proliferate and divide,thereby driving intestinal epithelial renewal.The continuous renewal of the intestinal epithelium requires the coordinated regulation of various signaling pathways.Once this regulation is out of balance,epithelial homeostasis will collapse.Mitochondria are highly mobile and dynamic organelles that continually fuse and divide,the opposing processes are important for cell fate determination and tissue homeostasis maintenance.However,the role of mitochondrial dynamic in intestinal homeostasis maintenance remains poorly understood.To study the role of mitochondrial dynamic in intestinal homeostasis maintenance,we constructed mouse models that could conditional knockout Mfn1,Mfn2,or Mfn1/2 in intestinal epithelium.The results showed that the single knockout of Mfn1 or Mfn2 had no significant effect on the epithelial structure,indicating that Mfn1,Mfn2 were functionally complementary.However,ablation of both Mfn1/2 in mouse epithelial cells lead to mitochondrial fragmentation,and intestinal epithelial differentiation was significantly affected including increased lysozyme~+ paneth cells,decreased Muc2~+ goblet cells and Chag A~+ endocrine cells.The loss of Mfn1/2 also leads to the apoptosis of TA cells in the crypt and the release of mt DNA,which leads to the production of Type ? IFN.Considering the possible effects of mesenchymal cells and immune cells on intestinal epithelial homeostasis,Mfn1/2 was knocked out at the level of intestinal organoids,loss of Mfn1/2 strongly inhibited the growth of organoids and led to the decrease of organoids'survival rate.Consistent with the in vivo results,loss of Mfn1/2 also led to cell apoptosis,release of mtDNA and production of Type I interferon.In addition,ablation of Mfn1/2 leads to mitochondrial dysfunctions,including decreased respiratory capacity,loss of membrane potential,decreased ATP content and increased reactive oxygen species.In in vitro rescue experiments,it was found that the Caspase inhibitor Qvdoph plus WNTligand Wnt3a could effectively inhibit the apoptosis caused by Mfn1/2 knock out and improve the survival rate of Mfn1/2organoids.Morever,we found that Mfn1/2 is necessary for the repair process after intestinal epithelial injury induced by X-ray irradiation.The Mfn1/2 knock out intestinal epithelium was unable to reconstruct villi-crypts construction after injury.In summary,mitochondrial dynamic plays an important role in maintaining mitochondrial function,mtDNA integrity,intestinal epithelial cell fate deter mination and repair of intestinal epithelial.It indicates that the dynamic changes of mitochondrial fission and fusion are important for the maintenance of intestinal epithelial homeostasis.