controlled study human 116 human cell male priority journal article 96 Humans 92 Male 83 nonhuman 61 female 54 protein expression 54 Female 50 animal cell 47 Animals 45 adult 43 animal experiment 42 mouse 38 Adult 34 Middle Aged 29 animal model 29 Mice 28 cell proliferation 28 human tissue 27 in vitro study 26 Aged 23 aged 23 clinical article 23 signal transduction 23 Spermatozoa 22 metabolism 22