Testicular Glycogen Metabolism: An Overlooked Source of Energy for Spermatogenesis?

Abstract

The incidence of male infertility has been increasing over the years and is now becoming a serious health problem. This trend has been followed by an increase in metabolic diseases, which are known to induce clear alterations in testicular metabolism, although the underlying mechanismremain unclear. Testicular metabolism displays several unique features, with testicular somatic cells being central in providing the conditions needed for spermatogenesis, including its nutritional and hormonal support. In addition to glucose and lactate, the two main energy sources used by the testis, glycogen is also present in testicular cells. Glycogen metabolism is a potential source of glucose to both testicular somatic (namely Sertoli and Leydig cells) and germ cells. Many of the enzymes involved in the pathways of the synthesis and degradation of glycogen were identified in these cells, emphasising the relevance of this complex carbohydrate. Glycogen, however, has other non-canonical functions in testicular cells; besides its role as a source of energy, it is also associated with events such as cellular differentiation and apoptosis. In this review, we address the relevance of testicular glycogen metabolism, focusing on its role in Sertoli and Leydig cells and spermatogenesis. In addition, all the available information on the role of glycogen and related pathways in male infertility cases is discussed. Our discussion highlights that glycogen metabolism has been somewhat overlooked in testis and its contribution to spermatogenesis may be underestimated.