Hyperhomocysteinemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression

Hyperhomocysteinemia has been shown to be associated with neurodegenerative diseases; however, lesions or histological changes and mechanisms underlying homocysteine-induced injury in olfactory bulb neurons remain unclear. In this study, hyperhomocysteinemia was induced in apolipoprotein E-deficient mice with 1.7% methionine. Pathological changes in the olfactory bulb were observed through hematoxylin-eosin and Pischingert staining. Cell apoptosis in the olfactory bulb was determined through terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Transmission electron microscopy revealed an abnormal ultrastructure of neurons. Furthermore, immunoreactivity and expression of the hairy enhancer of the split 1 (Hes1) and Hes5 were measured using immunohistochemistry, immunofluorescence, and western blot assay. Our results revealed no significant structural abnormality in the olfactory bulb of hyperhomocysteinemic mice. However, the number of TUNEL-positive cells increased in the olfactory bulb, lipofuscin and vacuolization were visible in mitochondria, and the expression of Hes1 and Hes5 decreased. These findings confirm that hyperhomocysteinemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression.