Age-dependent effects of hyperhomocysteinemia on neural differentiation and retinal development

Abstract

Hyperhomocysteinemia (HHcy), characterized by elevated homocysteine levels, is linked to developmental abnormalities, yet its impact on early eye development remains poorly understood. Given the well-documented neurotoxic effects of HHcy on central nervous system (CNS) development, this study aimed to investigate the age-specific effects of HHcy on eye development, focusing on retinal morphology, ultrastructure, vascular integrity, DNA integrity, apoptosis, and neural survival and differentiation. Fertilized Gallus domesticus embryos received 20 μmol homocysteine at embryonic day 2 (E2) and were analyzed at E6 and E10, key stages of eye organization and retinal layering. Although HHcy exposure did not alter retinal thickness, ultrastructural abnormalities indicating subcellular stress, such as dilated perinuclear space and rough endoplasmic reticulum cisternae, were observed. Disruptions on vascular integrity, induced by HHcy exposure were evident at both ages. DNA damage and upregulation of cell cycle regulators were noted at E6 but normalized by E10. Despite this, a reduction in cell proliferation was observed at both ages. Apoptosis increased at E10, suggesting heightened cell death during later retinal development. Neural differentiation and expression of neurotrophic factors were also impaired. Although overall retinal morphology appeared intact, HHcy induced significant molecular and structural disruptions, indicating a multifactorial, temporally dynamic mechanism of toxicity. These findings highlight the sensitivity of developing eye tissues to metabolic imbalance and suggest that even transient elevations in HHcy can interfere with critical developmental processes. This study underscores the potential role of HHcy in eye congenital anomalies and emphasizes the importance of maintaining homocysteine homeostasis during early embryogenesis.