LABEL-FREE QUANTITATIVE PROTEOMICS REVEAL PROTEIN NETWORKS AND ASSOCIATED BIOLOGICAL PROCESSES IN ANDROGEN DEPRIVED MOUSE SEMINAL VESICLES IN RESPONSE TO 17-β-ESTRADIOL (E2) TREATMENT

Purpose: Androgen deprivation therapy (ADT) remains the primary treatment strategy for inhibiting prostate cancer progression. However, systemic ablation of androgen-mediated signaling induces various metabolic disorders, cognitive decline, and osteoporosis. Therefore, like in menopausal women, 17-β-estradiol (E2) supplementation has been suggested as a treatment to reduce side effects associated with ADT. A recent clinical trial utilizing transdermal estrogen patches reported reduced osteoporosis markers and hot flashes. Estrogen receptors ER) are expressed in the male reproductive system and play a role alongside androgens in maintaining function and growth. Under normal physiological conditions, increased E2 concentrations induce an inhibitory effect on the size of the male reproductive organs, including the seminal vesicles (SV); however, under androgen depletion, E2 supplementation has been reported to reduce the atrophy of the SV in mice. In this study, we report for the first time a discovery-driven proteomic analysis of E2’s effects on the SV in mice under the conditions of surgical castration to model patients undergoing ADT. Methods: Surgically castrated mice (n=4) were subcutaneously injected with E2 (treated group) or vehicle (control) daily for five days and sacrificed to obtain SV. Proteins were extracted, reduced, alkylated, and digested with trypsin for analyses using data-dependent microflow liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) on LTQ Orbitrap Velos ProTM (Thermo Fisher Scientific). MS/MS data was searched against the UniProt Mouse protein database using Sequest in Proteome Discoverer (Thermo Fisher Scientific) and MaxQuant (Max Planck Institute). Validation of protein and label-free quantification (LFQ), combining spectral counting and total TIC, were performed using Scaffold (Proteome Software) to identify significantly affected proteins. Post-hoc t-test was performed to identify differences in protein abundances between groups. Regulated proteins we mapped to protein interaction networks and biological functions employing Ingenuity Pathway Analysis® (IPA®, Qiagen). Targeted proteomics- sed validation of significant candidate proteins is ongoing, and data will be analyzed using Skyline TM (MacCoss Lab, University of Washington). Results: Our discovery-driven LC–ESI-MS/MS analyses identified 7000 proteins with high confidence from the SV of E2-treated and control mice. IPA®-based bioinformatics of the E2-regulated proteins showed molecular and cellular functions-associated enrichment of carbohydrate metabolism, DNA replication, recombination, and repair, as well as free radical scavenging. The topmost regulated protein interaction network represented cell cycle, cell signaling, and small molecule biochemistry. Enhanced activation of the estrogen receptor β (ESR2) was implicated by the molecule activity predictor (MAP) tool of IPA®. Additionally, MAP predicted that the protein interaction represented within this network might impact disease and physiological processes associated with the proliferation of prostate cancer and regulation of gonadal cells. Furthermore, we were able to screen several preclinical biomarkers that participate in androgen receptor activity, modulating ER-mediated transcription and reproductive system development and function. Targeted proteomics-based validation of these biomarkers is ongoing. Conclusion: Our study aims to provide an in-depth account of the alterations occurring at the protein level in the SVs in response to E2 supplementation during ADT and to select and validate preclinical biomarkers for prognostic and therapeutic applications.