Morinda officinalis oligosaccharides mitigate depression-like behaviors in hypertension rats by regulating Mfn2-mediated mitophagy

Dahl salt-sensitive rats fed with a high-salt diet were stimulated by chronic unpredictable mild stress to mimic hypertension with depression. Primary astrocytes and neurons were isolated from these rats. Astrocytes underwent LPS stimulation to simulate the inflammatory astrocytes during depression. MOOs were administrated at 0.1 mg/g/day in vivo and 1.25, 2.5, and 5 mg/mL in vitro. Mitophagy was inhibited using 5 mM 3-methyladenine (3-MA). Astrocyte-mediated neurotoxicity was detected by co-culturing astrocytes and neurons.

MOOs decreased systolic pressure, diastolic pressure, and mean arterial pressure, thereby improving depression-like behavior, including behavioral despair, lack of enthusiasm, and loss of pleasure during hypertension with depression. Furthermore, MOOs inhibited inflammation, astrocytic dysfunction, and mitochondrial damage in the brain. Then, MOOs promoted autophagosome and lysosome enriched in mitochondria in LPS-stimulated astrocytes. MOOs suppressed mitochondrial damage and the release of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β in astrocytes undergoing LPS stimulation. Importantly, MOOs rescued the impaired neurons co-cultured with astrocytes. The effects of MOOs on LPS-stimulated astrocytes were reversed by 3-MA. Finally, MOOs upregulated LPS-downregulated Mfn2 expression in astrocytes. Mfn2 inhibition partly reversed the effects of MOOs on hypertension with depression. Intriguingly, Mfn2 suppression activated PI3K/Akt/mTOR pathway during MOOs treatment.

Astrocytes develop neuroinflammation in response to mitochondrial damage during hypertension with depression. MOOs upregulated Mfn2 expression to activate the PI3K/Akt/mTOR pathway-mediated mitophagy, thereby removing impaired mitochondria in astrocytes.