Abstract
Aims: To understand the molecular pathways involved in oxidative stress (OS)-mediated sperm dysfunction against a hypoxic and hyperthermic microenvironment backdrop of varicocele through a proteomic approach.
Results: Protein selection (261) based on their role in redox homeostasis and/or oxidative/hyperthermic/hypoxic stress response from the sperm proteome data set of unilateral varicocele (UV) in comparison with fertile control displayed 85 to be differentially expressed. Upregulation of cellular oxidant detoxification and glutathione and reduced nicotinamide adenine dinucleotide (NADH) metabolism accompanied with downregulation of protein folding, energy metabolism, and heat stress responses were observed in the UV group. Ingenuity pathway analysis (IPA) predicted suppression of oxidative phosphorylation (OXPHOS) (validated by Western blotting [WB]) along with augmentation in OS and mitochondrial dysfunction in UV. The top affected networks indicated by IPA involved heat shock proteins (HSPs: HSPA2 and HSP90B1). Their expression profile was corroborated by immunocytochemistry and WB. Hypoxia-inducible factor 1A as an upstream regulator of HSPs was predicted by MetaCore. Occurrence of reductive stress in UV spermatozoa was corroborated by thiol redox status.
Innovation: This is the first evidence of a novel pathway showing aberrant redox homeostasis against chronic hypoxic insult in varicocele leading to sperm dysfunction.
Conclusions: Upregulation of antioxidant system and dysfunctional OXPHOS would have shifted the redox balance of biological redox couples (GSH/GSSG, NAD(+)/NADH, and NADP(+)/NADPH) to a more reducing state leading to reductive stress. Chronic reductive stress-induced OS may be involved in sperm dysfunction in infertile men with UV, where the role of HSPs cannot be ignored. Intervention with antioxidant therapy warrants proper prior investigation.