The role of nitric oxide-cGMP pathway in selegiline antidepressant-like effect in the mice forced swim test

Fasting-mimicking diet alleviates inflammatory pain by inhibiting neutrophil extracellular traps formation and neuroinflammation in the spinal cord

BACKGROUND

Neutrophil extracellular traps (NETs) promote neuroinflammation and, thus, central nervous system (CNS) disease progression. However, it remains unclear whether CNS-associated NETs affect pain outcomes. A fasting-mimicking diet (FMD) alleviates neurological disorders by attenuating neuroinflammation and promoting nerve regeneration. Hence, in this study, we explore the role of NETs in the CNS during acute pain and investigate the role of FMD in inhibiting NETs and relieving pain.

METHODS

The inflammatory pain model was established by injecting complete Freund's adjuvant (CFA) into the hind paw of mice. The FMD diet regimen was performed during the perioperative period. PAD4 siRNA or CI-amidine (PAD4 inhibitor) was used to inhibit the formation of NETs. Monoamine oxidase-B (MAO-B) knockdown occurred by AAV-GFAP-shRNA or AAV-hSyn-shRNA or was inhibited by selegiline (an MAO-B inhibitor). The changes in NETs, neuroinflammation, and related signaling pathways were examined by western blot, immunofluorescence, ELISA, and flow cytometry.

RESULTS

In the acute phase of inflammatory pain, NETs accumulate in the spinal cords of mice. This is associated with exacerbated neuroinflammation. Meanwhile, inhibition of NETs formation alleviates allodynia and neuroinflammation in CFA mice. FMD inhibits NETs production and alleviates inflammatory pain, which is enhanced by treatment with the NETs inhibitor CI-amidine, and reversed by treatment with the NETs inducer phorbol 12-myristate 13-acetate (PMA). Mechanistically, the neutrophil-recruiting pathway MAO-B/5-hydroxyindoleacetic acid (5-HIAA) / G-protein-coupled receptor 35 (GPR35) and NETs-inducing pathway MAO-B/ Reactive oxygen species (ROS) are significantly upregulated during the development of inflammatory pain. MAO-B is largely expressed in astrocytes and neurons in the spinal cords of CFA mice. However, knockdown or inhibition of MAO-B effectively attenuates CFA-induced inflammatory pain, NETs formation, and neuroinflammation in the spinal cord. Moreover, within rescue experiments, MAO-B inhibitors synergistically enhance FMD-induced pain relief, NETs inhibition, and neuroinflammation attenuation, whereas supplementation with MAO-B downstream molecules (i.e., 5-HIAA and PMA) abolished this effect.

CONCLUSIONS

Neutrophil-released NETs in the spinal cord contribute to pain development. FMD inhibits NETs formation and NETs-induced neuroinflammation by inhibiting the MAO-B/5-HIAA/GPR35 and MAO-B/ROS pathways in astrocytes and neurons, thereby relieving pain progression. Video Abstract.

Mitochondrial NAD(P)+ Transhydrogenase is Unevenly Distributed in Different Brain Regions, and its Loss Causes Depressive-like Behavior and Motor Dysfunction in Mice

NAD(P)⁺ transhydrogenase (NNT) links redox states of the mitochondrial NAD(H) and NADP(H) via a reaction coupled to proton-motive force across the inner mitochondrial membrane. NNT is believed to be ubiquitously present in mammalian cells, but its expression may vary substantially in different tissues. The present study investigated the tissue distribution and possible roles of NNT in the mouse brain. The pons exhibited high NNT expression/activity, and immunohistochemistry revealed intense NNT labeling in neurons from brainstem nuclei. In some of these regions, neuronal NNT labeling was strongly colocalized with enzymes involved in the biosynthesis of 5-hydroxytryptamine (5-HT) and nitric oxide (NO), which directly or indirectly require NADPH. Behavioral tests were performed in mice lacking NNT activity (Nnt^-/-, mice carrying the mutated Nnt^C57BL/6J allele from the C57BL/6J strain) and the Nnt^+/+ controls. Our data demonstrated that aged Nnt^-/- mice (18-20 months old), but not adult mice (3-4 months old), showed an increased immobility time in the tail suspension test that was reversed by fluoxetine treatment, providing evidence of depressive-like behavior in these mice. Aged Nnt^-/- mice also exhibited behavioral changes and impaired locomotor activity in the open field and rotarod tests. Despite the colocalization between NNT and NO synthase, the S-nitrosation and cGMP levels were independent of the Nnt genotype. Taken together, our results indicated that NNT is unevenly distributed throughout the brain and associated with 5-THergic and NOergic neurons. The lack of NNT led to alterations in brain functions related to mood and motor behavior/performance in aged mice.