Nicotinamide ameliorates mitochondria-related neuronal apoptosis and cognitive impairment via the NAD+/SIRT3 pathway

by Selleckchem | Aug 16 2023

Emerging evidence suggests that mitochondria play a central role in mental health disorders including schizophrenia. Here we investigated whether nicotinamide (NAM) normalized cognitive impairment via a mechanism involving the mitochondrial Sirtuin 3 (SIRT3) pathway. The 24 h maternal separation (MS) rat model was used to mimic schizophrenia-associate phenotypes. Schizophrenia-like behaviors and memory impairments were detected using the pre-pulse inhibition test, novel object recognition test, and Barnes maze test, and neuronal apoptosis was characterized using multiple assays. SIRT3 activity was inhibited pharmacologically or by knockdown in HT22 cells, and BV2 microglia and SIRT3-knockdown HT22 cells were co-cultured in vitro. Mitochondrial molecules were measured by western blotting, and mitochondrial damage was measured with reactive oxygen species and mitochondrial membrane potential assays. Proinflammatory cytokines were assayed by ELISA and microglial activation was detected by immunofluorescence. MS animals showed behavioral and cognitive impairment and increased neuronal apoptosis. Supplementation with NAM or administration of honokiol, a SIRT3 activator, reversed all of the changes in behavioral and neuronal phenotypes. Administration of the SIRT3 inhibitor 3-TYP in control and NAM-treated MS rats caused behavioral and neuronal phenotypes similar to MS. In vitro, inhibition of SIRT3 activity with 3-TYP or by knockdown in HT22 cells increased ROS accumulation and caused neuronal apoptosis in a single-culture system. In co-culture systems, SIRT3 knockdown in HT22 cells activated BV2 microglia and increased levels of TNF-α, IL-6, and IL-1β. The administration of NAM blocked these alterations. Taken together, these data suggest that NAM can rescue neuronal apoptosis and microglial over-activation through the nicotinamide adenine dinucleotide (NAD+)-SIRT3-SOD2 signaling pathway, furthering our understanding of the pathogenesis of schizophrenia and providing avenues for novel treatments.

Comments:

The study you mentioned investigates the potential role of mitochondria in mental health disorders, particularly schizophrenia, and explores whether nicotinamide (NAM) can normalize cognitive impairment through the mitochondrial Sirtuin 3 (SIRT3) pathway. The researchers used a rat model of maternal separation (MS), which is known to exhibit schizophrenia-like behaviors and cognitive impairments.

In the study, several behavioral tests were conducted to assess schizophrenia-like behaviors and memory impairments in the MS rats. The pre-pulse inhibition test, novel object recognition test, and Barnes maze test were employed for this purpose. Neuronal apoptosis, a form of cell death, was also evaluated using various assays.

The researchers pharmacologically inhibited or knocked down SIRT3 activity in HT22 cells, a cell line used in neuroscience research, as well as BV2 microglia cells. In vitro co-culture experiments were performed with SIRT3-knockdown HT22 cells and BV2 microglia. They measured mitochondrial molecules through western blotting and assessed mitochondrial damage using reactive oxygen species (ROS) and mitochondrial membrane potential assays. Additionally, proinflammatory cytokines were assayed, and microglial activation was detected using immunofluorescence.

The results of the study showed that MS animals exhibited behavioral and cognitive impairments, as well as increased neuronal apoptosis. However, supplementation with NAM or administration of honokiol, a SIRT3 activator, reversed these changes in behavioral and neuronal phenotypes. Conversely, administration of the SIRT3 inhibitor 3-TYP in both control and NAM-treated MS rats led to similar behavioral and neuronal phenotypes observed in the MS model.

In the in vitro experiments, inhibiting SIRT3 activity using 3-TYP or knockdown in HT22 cells resulted in increased ROS accumulation and neuronal apoptosis in the single-culture system. In the co-culture system, SIRT3 knockdown in HT22 cells activated BV2 microglia and elevated levels of proinflammatory cytokines, such as TNF-α, IL-6, and IL-1β. However, the administration of NAM prevented these alterations.

Overall, the findings of this study suggest that NAM can rescue neuronal apoptosis and over-activation of microglia through the NAD+-SIRT3-SOD2 signaling pathway. These results contribute to our understanding of the underlying mechanisms involved in the pathogenesis of schizophrenia and offer potential avenues for novel treatments.