Table 1.

Summary of preclinical trials showing successful differentiation of various stem cell lines into steroidogenic Leydig-like cells

Ref.	Stem cells used	Study type	Design	Results
Lo et al[52]	Mouse mixed testicular stem cells (SP) containing spermatogonial, leydig cell, and myoid stem cells	In vivo	SCs were injected into the testes of sterile sertoli-cell only transgenic mice and transgenic mice with a targeted deletion of 4-kb pairs of the LH receptor gene	SP cell transplanted mice had increased time-dependent serum testosterone and spermatogenesis compared to non-SP cell transplanted mice
Yazawa et al[53]	Rat BM-MSCs	In vivo	BM-MSCs were injected into the testes of 3-wk old Sprague-Dawley rats	BM-MSCs differentiated into steroidogenic cells similar to Leydig cells
	Mouse MSCs		MSCs were transfected with Sf-1 followed by treatment with cAMP and cultured in Iscova’s MEM or DMEM with 10% fetal calf serum	Transfected cells differentiated into Leydig cells
Lue et al[51]	Unfractionated mouse bone marrow stem cells	In vitro	SCs were injected into the testes of busulfan treated mice and c-kit mutant homozygous mice	SCs differentiated into Leydig, Sertoli, and germ cells after 12 wk. Though germ cells were lacking in c-kit mutant mice
Gondo et al[63]	Mouse AMCs	In vitro	AMCs and BMCs were transfected with SF-1 and cultured with Medium A	AMCs were more likely to differentiate into adrenal-type steroidogenic cells with increased production of corticosterone
	Mouse BMCs			BMCs were more likely to differentiate into gonadal-type steroidogenic cells with increased production of testosterone
Yazawa et al[54]	Human BM-MSCs	In vitro	BM-MSCs were transfected with LRH-1 followed by treatment with cAMP and cultured in DMEM with 10% fetal calf serum	Transfected cells expressed CYP17 and produced testosterone
Yazawa et al[55]	UC-MSCs	In vitro	UC-MSCs were transfected with SF-1 followed by treatment with cAMP and cultured in DMEM/Ham’s F-12 supplemented with 0.1% BSA	Transfected cells differentiated into cells with similar characteristics to granulosa-luteal cells
Wei et al[62]	Human UC-MSCs	In vitro	UC-MSCs and BM-MSCs were transfected with SF-1 and cultured in the presence of cAMP	Differentiated UC-MSCs had higher expression of steroidogenic mRNAs. They also secreted significantly greater amounts of testosterone and cortisol than BM-MSCs
	Human BM-MSCs
Yazawa et al[64]	Rat BM-MSCs	In vivo	BM-MSCs were transplanted into prepubertal testes	MSCs were able to differentiate into steroidogenic Leydig cells in vivo. SF-1 expression was also detected
Yang et al[56]	Rat ADSCs	In vivo	ADSCs were injected into Sprague-dawley rats that had been treated with D-gal (aging model) or saline (control) for 8 wk	ADSCs migrated to damaged areas, reduced the number of apoptotic Leydig cells, and upregulated enzymes to increase testosterone levels in the testis in those treated with D-gal
Yang et al[58]	Mouse ESCs	In vivo	ESCs were cultured with cAMP, SF-1, and FSK. These derived Leydig-like cells were then injected into Sprague-dawley rats treated with EDS	FSK enhanced the differentiation of mESCs into Leydig-like cells. Subsequent treatment with these newly differentiated cells led to increased testosterone levels in EDS-treated rats
Hou et al[57]	Human BM-MSCs	In vitro	Experimental - BM-MSCs were cultured in conditional medium with different concentrations of HMG/LH Control - BMSCs were cultured in FBS in DMEM medium with normal sodium	Experimental culture medium induced the differentiation of BMSCs into Leydig cells
Zhang et al[59]	Rat SLCs	In vitro	SLCs were cultured in a seminiferous tubule model using media containing NGF. The proliferative capacity of SLCs, along with testosterone production, and steroidogenic gene/protein expression was measured	NGF significantly promoted the proliferation of stem Leydig cells and also induced steroidogenic enzyme gene expression and 3β-HSD protein expression
Odeh et al[60]	Rat SLCs	In vitro	SLCs were cultured on the surfaces of seminiferous tubules in a media containing PDGF-AA or PDGF-BB for up to 4 wk. SLC proliferation and differentiation were measured	Both PDGF-AA and PDGF-BB stimulated SLC proliferation during the first week of culture. After this first week, PDGF-AA had a stimulatory effect on SLC differentiation. PDGF-BB began inhibiting differentiation after this first week
Li et al[61]	Rat SLCs	In vitro	SLCs were cultured on the surface of seminiferous tubules to assess the ability of factors from the seminiferous tubules to regulate their proliferation and their subsequent entry into the Leydig cell lineage	SLC proliferation was stimulated by DHH, FGF2, PDGF, and activin. Differentiation was activated by DHH, lithium-induced signaling, and activin, and inhibited by TGF-β, PDGF-BB, and FGF2

BM-MSCs: Bone marrow-derived mesenchymal stem cells; AMCs: Adipose derived mesenchymal cells; BMCs: Bone marrow cells; UC-MSCs: Umbilical cord mesenchymal stem cells; ADSCs: Adipose-derived mesenchymal stem cells; ESCs: Embryonic stem cells; SLCs: Stem leydig cells; LH: Luteinizing hormone; HMG: Human menopausal gonadotropin; FBS: Fetal bovine serum; PDGF-AA: Platelet-derived growth factor alpha; DHH: Desert hedgehog; FGF: Fibroblast growth factor; LRH-1: Liver receptor homolog-1; SF-1: Steroidogenic factor-1; BSA: Bovine serum albumin; cAMP: Cyclic adenosine monophosphate; EDS: Ethane dimethanesulfonate; NGF: Nerve growth factor.