Mixed testicular atrophy related to atherosclerosis: first lessons from the ApoE−/−/ LDL receptor−/− double knockout mouse model

Age-related testicular changes are associated with declining spermatogenesis and testosterone levels. A relationship to atherosclerosis has never been investigated systematically. The ApoE^−/−/LDL receptor^−/− double knockout mouse model, providing a remarkable homology to human atherosclerosis, is an ideal tool to investigate spermatogenetic alterations in this context. Testes (n = 10) from ApoE^−/−/LDL receptor^−/− double knockout mice at the age of 80 weeks were perfused in vivo with contrast agent, harvested and scanned with micro-CT at (4.9 μm³) voxel size. Testes (n = 8) of C57/BL mice at the same age served as controls. Testis volume (mm³) and total vascular volume fraction (mm³) were quantified using micro-CT. Serum testosterone levels were determined. Testicular histology and epididymal sections were analysed for tubular structure, spermatogenetic scores and sperm count. The expression of protamine 2 as a marker for elongated spermatids, inflammation markers (CD4, F4/80) and hypoxia inducible factor 1 alpha (HIF1 alpha) were investigated using immunohistochemistry. ApoE^−/−/LDL receptor^−/− double knockout mice exhibit diminished testis and vascular volume fraction with respect to that of controls (p < 0.001). These findings were associated with a reduction of testosterone levels (p < 0.001). Mixed atrophy was present in 41% of the seminiferous tubuli in ApoE^−/−/LDL receptor^−/− double knockout mice at the age of 80 weeks. Sperm counts from the epididymis demonstrated a significant decrease in ApoE^−/−/LDL receptor^−/− double knockout mice (p < 0.001). In addition, sperm specific protamine 2 expression was decreased in testicular tissue and epididymis of ApoE^−/−/LDL receptor^−/− double knockout mice compared with that of control mice. Peritubular inflammatory infiltration and the expression of the hypoxia related marker was observed. Mixed testicular atrophy in ApoE^−/−/LDL receptor^−/− double knockout mice is linked to reduced testis volume, vascular volume fraction and low testosterone serum levels, suggesting a direct relation between atherosclerosis and disturbed spermatogenesis.