Fig. 7.

Diagram illustrating the proposed sphingosine accumulation caused by gut microbiota dysbiosis leads to damage to the spermatogenic process. The accumulation of sphingosine, mainly owing to the dramatically decreased abundance of Olsenella, Lachnospiraceae_UCG_002 and Ruminococcaceae_NK4A214_group in the prediabetic sheep model. The accumulation of sphingosine was transferable to the testis through the blood circulation, which increased the level of apoptosis of testicular tissues, resulting in the arrest of S2 Round Std. Meanwhile, adding melatonin restored the status of gut microbiota dysbiosis and sphingosine accumulation in the prediabetic sheep model, as well as improving abnormal spermatogenesis