Modelling of Mouse Spermatogonial Stem Cell Niche for Designing 3D scaffolds for in vitro Spermatogenesis

Abstract

The homeostasis of male genitalia in mammals is maintained by a group of stem cells called spermatogonial stem cells (SSCs) which replenishes worn out cells in the testicular tissue. In mouse, these cells are housed by specialised tubular structures called seminiferous tubules. The SSC niche is found dispersed on the basal lamina, which is a two dimensional extracellular matrix along the circumference of seminiferous tubules. The Myoid, Sertoli and Leydig cells support SSCs while self-renewal and differentiation. The self-renewal and migration of SSCs takes place along the lateral direction and differentiation occurs medially towards the lumen of seminiferous tubules. The differentiation and self-renewal occurs in a cycle with each cycle possessing 12 stages of seminiferous epithelium. The self-renewal and commitment for differentiation of stem cells occurs from stages X – VIII of seminiferous epithelium. A MatlabTM program was developed to simulate the behavior of SSCs in their niche within the seminiferous tubules with logical rules. The migration, self-renewal and differentiation of SSCs was modelled according to the logical parameters provided by researches over the past century. The behavior of SSCs in their niche was assumed to be dependent on cell density in that niche area. The SSCs responded to the density stress imposed on them by their neighbouring cells which forced them migrate into a space with lower stress. Similarly, division and differentiation was also controlled by density stress through various thresholds. The model outcome was validated with literature. The model predicted that there was 12 Asingle cells, 15 Apaired cells and 19 Aaligned cells per 1000 Sertoli cells in the niche of
mouse. With these metrics in concern, a biopolymer scaffold was prepared by using alginate to mimic the testicular tissue. Polymerisation was performed by the process of ionotropic gelation with CaCl2 as the crosslinker. Channels of diameter from 100 μm to 250 μmm were obtained in the anisotropic gel. The tubular nature of the scaffold mimicked seminiferous tubules in dimension. Physiochemical characterization like SEM, FTIR, Mechanical analysis of the scaffold was done on the scaffold.