L‐Dopa Decarboxylase Mediates Apoptosis Through Regulation of PI3K / AKT Pathway in Response to DENV Infection

L-dopa decarboxylase (DDC) is the biosynthetic enzyme of dopamine and serotonin. Although DDC has been originally studied for its role in neurotransmission, it has also been detected in peripheral organs, where it is implicated in cellular homeostasis. DDC has been identified by our research team as a negative regulator of dengue virus (DENV) replication in liver cells. The latter has been attributed, at least in part, to the physical interaction of DDC protein with phosphatidylinositol 3-kinase (PI3K), and its biosynthetic function. PI3K/AKT signaling and cell survival are manipulated by DENV to favor its replication. Based on the above, we investigated whether DDC exerts its antiviral activity against DENV propagation through modulation of DENV-induced cell death and especially apoptosis. Specifically, DDC silencing in Huh7.5 cells (shDDC) significantly reduced virus-induced cytopathic effect compared to the control cells (shControl). This finding was accompanied by suppression of both early and later stages of apoptosis in the silenced cells, as shown by Annexin V/PI staining and TUNEL assay, respectively. Accordingly, upon infection, shDDC cells showed suppressed activation of key caspases, BCL-2 family members and TRAIL-receptor genes that modulate the apoptotic cascade, compared to the control cells. Moreover, mitochondrial analysis in DENV-infected cells revealed that, upon DDC silencing, a less pronounced disruption of mitochondrial membrane potential and network integrity, higher respiratory capacity, lower ROS production, and reduced cytochrome c release were observed. As the PI3K/AKT pathway is known to be affected by both DENV and DDC, next we assessed whether DDC is involved in the virus-induced apoptosis through this axis. For this, we quantified the reduction of p-AKT and p-mTOR levels caused by DENV infection in the two cell lines, which was found greater in the shControl cells. Finally, chemical inhibition of AKT phosphorylation abolished the differences in cell viability and apoptosis between the two cell lines. In total, our findings highlight the suppressive role of DDC against DENV replication by modulating the PI3K/AKT-dependent apoptotic signaling.