Initial germ cell to somatic cell ratio impacts the efficiency of SSC expansion in vitro

Spermatogonial Stem Cell (SSC) expansion in vitro remains a major challenge in efforts to preserve fertility among pubertal cancer survivor boys. The current study focused on innovative approaches to optimize SSC expansion. Six- to eight-week-old CD-1 murine testicular samples were harvested by mechanical and enzymatic digestion. Cell suspensions were incubated for differential plating (DP). After DP, we established two experiments comparing single vs. repetitive DP (S-DP and R-DP, respectively) until passage 2 (P2) completion. Each experiment included a set of cultures consisting of 5 floating-to-attached cell ratios (5, 10, 15, 20, and 25) and control cultures containing floating cells only. We found similar cell and colony count drops during P0 in both S- and R-DP. During P2, counts increased in S-DP in middle ratios (10, 15, and especially 20) relative to low and high ratios (5 and 25, respectively). Counts dropped extensively in R-DP after passage 2. The superiority of intermediate ratios was demonstrated by enrichment of GFRα1 by qPCR. The optimal ratio of 20 in S-DP contained significantly increased proportions of GFRα1-positive cells (25.8±5.8%) as measured by flow cytometry compared to after DP (1.9±0.7%, p<0.0001), as well as positive immunostaining for GFRα1 and UTF1, with rare Sox9-positive cells. This is the first report of the impact of initial floating-to-attached cell ratios on SSC proliferation in vitro.

Abbreviations: SSC: spermatogonial stem cells; DP: differential plating; NOA: non-obstructive azoospermia; MACS: magnetic-activated cells sorting; FACS: fluorescence-activated cells sorting