Abstract
Florfenicol (FLO) is one of the most popular antibiotics used in veterinary clinic and aquaculture. FLO can inhibit both bacterial and mitochondrial protein synthesis. However, the effects of FLO on mitochondrial function and cellular homeostasis remain unclear. Here we show that FLO inhibits expression of mitochondrial DNA-encoded proteins, decreases mitochondrial membrane potential, and promotes generation of reactive oxygen species (ROS) in vitro. As a result, activities of mitochondrial respiratory chain complex I and IV and the cellular ATP level are decreased and mitochondrial morphology is damaged. FLO represses cell growth and proliferation by suppression of phosphorylation of p70S6K through AMPK/mTOR/p70S6K pathway. Furthermore, FLO also induces G0/G1 cell cycle arrest via increase of p21 levels through activating ROS/p53/p21 pathway. Moreover, the clearance of damaged mitochondria by autophagy is impaired, leading to cell proliferation inhibition and promotes cell senescence. In addition, FLO-induced upregulation of cytosolic p53 may contribute to mitophagy deficiency via regulation of Parkin recruitment. In summary, our data suggest that florfenicol is an inhibitor of mitochondrial protein synthesis that can induce noticeable cytotoxicity. Thus, these findings can be useful for guiding the proper use of FLO and the development of safe drugs.
Highlights
In L cells, 293 T cells and Marc[145] cells treated for 24 h or 48 h. (B) Immunoblot analysis of multiple doses of FLO on protein levels of Cox I, Cox II, ATPase[6] and Cox IV in L cells treated for 24 h
Dysfunctional or damaged mitochondria are removed by a specific autophagic process called mitochondrial autophagy, which is critical for the maintenance of cell homeostasis, because damaged organelles cannot be diluted by cell proliferation[10]
We investigated the effect of FLO on mitochondrial function, cell proliferation and mitochondrial autophagy, to find out the mechanism of cytotoxicity caused by FLO-induced mitochondrial dysfunction
Summary
FLO inhibits expression of mitochondrial-encoded proteins and impairs mitochondrial function. These antibiotics induced different levels of cytotoxicity to L cells when cultured in glucose medium and more severe cytotoxicity was observed when L cells with damaged mitochondrial respiratory chain were grown in galactose medium (Supplementary Fig. S4B) Taken together, these results demonstrate that mitochondrial dysfunction is functionally important for FLO-mediated suppression of cell proliferation and cell cycle arrest. The co-treatment of FLO with NAC decreased the MTDR fluorescence levels relative to that of FLO-treated cells (Fig. 5F), which indicated that NAC-treatment restored mitophagy and promoted the clearance of damaged mitochondria in FLO-treated L cells These results reveal that FLO-induced mitophagy deficiency correlates with the inhibition of Parkin translocation to mitochondria, and the ROS scavenger NAC can partially restore the impaired mitophagy
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