The effect of autophagy and mitochondrial fission on Harderian gland is greater than apoptosis in male hamsters during different photoperiods

Abstract Background: Photoperiod is one of the important factors of mammalian seasonal rhythm. As an important photosensitive organ in addition to the eyes and pinecones, Harderian gland (HG) may respond to seasonal light cycle changes. Here, we studied the morphological differences in the HG of male striped dwarf hamsters (Cricetulus barabensis), a small mammal with annual rhythm under different photoperiods (short photoperiod, SP; moderate photoperiod, MP; long photoperiod, LP), and further investigated the molecular mechanisms related to these morphological differences.Results: Results showed that body weight, carcass weight, and HG weight were lower in the SP and LP groups than that in MP group. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining showed that random DNA fragmentation was observed in all three groups. The protein expression of bax/bcl2 and cytochrome C all have no significant difference between three groups, indicated that the level of apoptosis remained stable. Protein aggregation and mRNA expression of LC3 as well as the protein expression of LC3II/LC3I in the SP group were higher than that in the MP group. P62 protein aggregates and protein expression were lower in long photoperiod than other two groups. These results suggested that autophagy level was the lowest in MP group. The protein expression of ATP synthase and mitochondrial fission factor showed highest in MD group, while citrate synthase, dynamin-related protein1, and fission1 remain unchanged during three groups. These indicate that the mitochondrion fission and energy function are slightly reduced in SD and LD groups.Conclusion: In summary, since the fact that there is no significant change in the level of apoptosis in HGs under different photoperiods, the significant up-regulation of autophagy level in the long and short photoperiod may be the main factor leading to the loss of HG weight as well as the reduced mitochondrial energy supply.