Two-Player Game in a Complex Landscape: 26S Proteasome, PKA, and Intracellular Calcium Concentration Modulate Mammalian Sperm Capacitation by Creating an Integrated Dialogue-A Computational Analysis.

Angela Taraschi,Giulia Capacchietti,Mohamad Al Iskandarani,Marina Ramal-Sanchez,Luca Valbonetti,Israiel Tagaram,Juliana Machado-Simoes,Costanza Cimini,Nicola Bernabò,Samia Mokh,Fadl Moussa,Alessia Colosimo,Barbara Barboni

doi:10.3390/ijms21176256

Abstract

Recent experimental findings suggest the involvement of the 26S proteasome, the main protease active in eukaryotic cells, in the process that leads mammalian sperm to become fully fertile, so-called capacitation. Unfortunately, its role in male gametes signaling is still far from being completely understood. For this reason, here, we realized a computational model, based on network theory, with the aim of rebuilding and exploring its signaling cascade. As a result, we found that the 26S proteasome is part of a signal transduction system that recognizes the bicarbonate ion as an input terminal and two intermediate layers of information processing. The first is under the control of the 26S proteasome and protein kinase A (PKA), which are strongly interconnected, while the latter depends on intracellular calcium concentrations. Both are active in modulating sperm function by influencing the protein phosphorylation pattern and then controlling several key events in sperm capacitation, such as membrane and cytoskeleton remodeling. Then, we found different clusters of molecules possibly involved in this pathway and connecting it to the immune system. In conclusion, this work adds a piece to the puzzle of protease and kinase crosstalk involved in the physiology of sperm cells.

Highlights

Mammalian spermatozoa are infertile immediately after ejaculation and need to undergo functional maturation to acquire the competence to fertilize the female egg
A complex network of interactions involving the oviductal epithelial cells and the tubal fluid drives the functional maturation of the male gametes, thanks to a well-balanced action of inhibiting and activating molecular messages
Capacitation leads to an increase in sperm plasma membrane fluidity due to cholesterol loss [2,3], an increase in ionic influx by membrane hyperpolarization [4], and important changes in the protein phosphorylation pattern [5]

Summary

Introduction

Mammalian spermatozoa are infertile immediately after ejaculation and need to undergo functional maturation to acquire the competence to fertilize the female egg. Capacitation leads to an increase in sperm plasma membrane fluidity due to cholesterol loss [2,3], an increase in ionic influx by membrane hyperpolarization [4], and important changes in the protein phosphorylation pattern [5] In this context, the role of the 26S proteasome is emerging, i.e., the main protease in eukaryotic cells [6], formed by a multi-enzymatic complex with trypsin-like, chymotrypsin-like, and peptidylglutamyl peptide-hydrolyzing (PGPH) activities [7]. A huge amount of molecular data concerning sperm capacitation in several mammalian models are available, due to the large-scale adoption of the so-called –omics (proteomics, lipidomics, transcriptomics, etc.) and, the involvement of the 26S proteasome in this context was proposed These molecular data are still unorganized, and the 26S proteasome’s role in the flux of information that drives sperm physiology is still unclear. Here, we focused our model on studying the role of the 26S proteasome in mammalian sperm capacitation, aggregating all the molecular data available to date and realizing the network that represents its interactome (26SN)

Results and Discussion

Materials and Methods

Identification of 26SN Hubs

Identification of Bottleneck Nodes within 26SN

Enrichment Analysis