HC diet inhibited testosterone synthesis by activating endoplasmic reticulum stress in testicular Leydig cells

Emerging epidemiological studies indicate that hypercholesterolaemia is a risk factor for testosterone deficiency. However, the underlying mechanism is unclear. Testicular Leydig cells are the primary source of testosterone in males. To identify the effect and mechanism of cholesterol overload on Leydig cell function, rats were fed with a HC (HC) diet to induce hypercholesterolaemia. During the 16-week feeding period, serum testosterone levels were reduced in a time-dependent manner in rats fed the HC diet. Accordingly, these steroidogenic enzymes within the Leydig cells, including steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage cytochrome P450 (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD), were down-regulated. Notably, the HC-fed rats showed evident endoplasmic reticulum (ER) stress in the testis, including a dilated ER as an evident pathological change in the Leydig cell ultrastructure, up-regulated ER stress biomarker (binding immunoglobulin protein) levels and activation of the activating transcription factor 6 (ATF6)-related unfolded protein response pathway. Further analysis showed that when 4-phenyl butyric acid (4-PBA) was used to block ER stress in HC-fed rats for 8 weeks, the testosterone deficiency was significantly alleviated. Our findings suggested that high dietary cholesterol intake affected serum testosterone levels by down-regulating steroidogenic enzymes and that activated ER stress might serve as the underlying mechanism.