Differential protein expression in male and female human lumbar cerebrospinal fluid using iTRAQ reagents after abundant protein depletion

Cerebrospinal fluid (CSF) has become one of the most frequently used biological medium for physiological studies for neurological disorders due to its proximity to the brain and clinical availability; however, before undertaking a rational approach to biomarker discovery or diagnostics, it is crucial to understand the underlying characteristics of CSF proteome in subpopulations. In this study, we examined the differential expression of proteins in pooled male and female CSF utilizing isobaric tags for relative and absolute quantification (iTRAQ™) reagents after the depletion of six high abundant proteins using a multiple affinity removal system (MARS). A total of 219 proteins were identified (95% confidence level), and 12 proteins showed difference in expression levels. Eleven out of 12 differentially expressed proteins showed ratios of male/female between 1.15 and 1.29 (duplicate average), indicating a remarkable similarity between male and female CSF. One notable exception was the slightly lower expression level of ceruloplasmin (ferroxidase) in male CSF (0.81), a copper containing protein that catalyzes the conversion of ferrous iron to ferric iron with antioxidant properties. We also examined the levels of ceruloplasmin in each individual patient sample which constituted the pooled CSF using Western blot analysis which confirmed the lower expression levels of ceruloplasmin in male CSF.