mTOR coordinates many cellular processes in living organisms, regulating homeostasis, protein synthesis, transcription, autophagy, metabolism, brain function and the maturation of different tissues.
The discovery that regulation of mTOR signaling pathways correlates to persisting viral loads suggests that an infection by ZIKV may directly influence mTOR mechanics, promoting the survival of infected cells.
The mTOR signaling shows a vital role in neurological development, including the proliferation of neural stem cells, the development of neural circuits, plasticity and more complex functions.
A study conducted by Liang et al. demonstrated that NS4A and NS4B nonstructural protein from ZIKV can suppress the AKT-mTOR signaling pathway, which is the main responsible for controlling autophagy stimulation in eukaryotic cells, hence inducing autophagy.
The appelberg et al. emphasizes that changes to the AKT-mTOR signaling pathway are critical, not only for autophagy regulation, but for cortical development as well, as permanent inhibition may result in microcephaly.
This study showed how Zika virus may be related to mTOR 1 and mTOR 2 expressions. The comparative results to viral load emphasize the correlation between the virus and mTOR. Such correlation is of importance to ZIKV, for protein regulation pathways and virus interference on those pathways may turn out to be a factor related to its pathogenic mechanism.
Laboratory tests demonstrate a correlation between mTOR 1, mTOR 2 and defensive cells (macrophages and neutrophils), which may suggest that the virus, through modifications to those paths, may induce proliferation of those cells.
It is worth pointing out that mTORC1 may be correlated to the macrophage signaling process, as it is even possible to modulate the inflammatory process during an infection by ZIKV. Correlations exist with the autophagy process and even with the cellular cycle regulation in various flaviviruses, like dengue. Our study demonstrates a significant increase in mTORC1 expression levels during the whole infectious process, which reiterates the occurrence of autophagy inside tissues, as described in literature.
Regarding mTORC2, a significant reduction in expression may be observed along the ZIKV infection process, which is linked to cellular longevity and to maintenance processes in the infected cells. This reasoning becomes more evident when we consider mTORC2 shows increased expression during the cellular maintenance cycle and when attempting cellular repair.
Our study showed a correlation between mTOR 1 and 2 during ZIKV infection, and such correlation appears to be closely connected, not only to infection duration and viral load, but to infected tissues as well, as our experiments involved neural tissue and the reproductive system.
Studies such as Rothan, that verified changes in cellular metabolism during ZIKV infection, have correlated higher mTOR 1 expressions during an increase in viral load with a decrease in mTOR 2 in the same period, which corroborates our findings.
Our data, however, shows that a negative expression process for mTOR 2 with a positive expression for mTORC1 will occur both in mature neural cells, represented by the CF group, and in newborn cells, represented by CN. It is therefore possible to observe that ZIKV not only acts upon cellular differentiation, but on cellular metabolization and repair as well.
Our results appear to contribute to recent papers pointing to the relevance of mTOR to ZIKV maintenance and replication. Those findings demonstrate how mTOR is not only involved with cellular processing and maintenance.
Processes as autophagy are of great importance during the ZIKV infection, which is made clear by reviewing the results of Chiramel et al., that demonstrate how important mTOR pathways are to the autophagy process inside neural tissues during infection by ZIKV.
Collins et al. covered the importance of this pathway for macrophage inflammatory signaling. It makes clear how the mTOR pathways are a key to ZIKV maintenance and viral replication in very specific types of tissue, as those covered in the present work.
Detailed analyses of mTOR functions for other RNA viruses like SARS-CoV-2, Hepatitis C and Dengue 2 establish the relevance of mTOR pathways for the maintenance of infected cells and demonstrate how a reduced mTOR 2 expression may favor a viral infection, which is noticeable in the groups examined in our study.
In the present work, we were able to detect an important connection between mTOR 1 and mTOR 2 pathways during a ZIKV infection to cells from the nervous system and to cells from the female reproductive system. Also, that mTOR pathways are most important for the continuation of the ZIKV infection process during the infection period, and that such importance is not limited to cellular autophagy processes but reaches other cellular maintenance functions. It should be highlighted that the difference in expression from mTOR pathways in neural cells not only occurs in young neural cells, like those from newborn individuals, but in mature neural cells as well.