Role of Hemocytes in the Aging of Drosophila Male Germline

Stem cells are essential for the proper functioning of tissues, replacing damaged, senescent cells to ensure tissue regeneration. However, as age advances, the number of these stem cells can change, and their self-renewal abilities can become impaired, leading to disruption of homeostasis, loss of regenerative capacity, and, ultimately, deterioration of tissue function. In Drosophila testis, in addition to the germline and somatic cells involved in spermatogenesis, there are immune cells (hemocytes) with macrophage function. In our study, we aimed to investigate the role of hemocytes in maintaining germline stem cells throughout their lifespan. Our results show that in the absence of plasmatocytes and crystal immune cells, the number of germline stem cells (GSCs) and apoptotic germline cells also increases significantly during senescence, which may have detrimental effects on the differentiation processes of germline cells. The size of the hub increases in aged male testes. It is therefore conceivable that changes in the hub may induce dysfunction of differentiation processes. The fertility of aged immunodeficient animals is decreased. Furthermore, we show that the expression of the JAK/STAT signaling pathway, which is essential for the maintenance of the stem cell niche, is impaired in the lack of hemocytes. We found an increased expression of Socs36e, an inhibitor of JAK-STAT, which correlates with decreased JAK-STAT activity. Overexpression of Socs36e in the apical part of the germline led to a phenotype similar to the immunodeficient aged germline, where an increased GSC number and hub size were also observed. However, spermatogenesis was also disturbed in this case. Our study shows that hemocytes are required to regulate the number of GSCs. This regulation could be mediated through the JAK-STAT signaling pathway. These results may help to provide a more complex insight into the relationships between immune cells and stem cells.