SIRT1 Activator SRT1720 Fights Depression by Clearing Damaged Mitochondria

Depression affects roughly 280 million people globally, yet over a third of patients fail to respond adequately to existing antidepressants. Identifying new biological targets is therefore a clinical priority. Mitochondrial dysfunction and impaired mitophagy—the selective autophagy of damaged mitochondria—have emerged as contributors to depression pathology. SIRT1, a NAD⁺-dependent deacetylase abundantly expressed in brain regions including the hippocampus, is known to regulate autophagy and mitochondrial quality control, and is downregulated in depressed patients. This study asked whether pharmacological activation of SIRT1 could reverse depression-like states and whether mitophagy mediates that effect.

Male BALB/c mice received a single intraperitoneal injection of LPS (0.83 mg/kg) to induce neuroinflammation and depression-like behaviors. The SIRT1 activator SRT1720 (50 mg/kg, i.p.) was given two hours before LPS. Behavioral testing 24 hours later showed that LPS-treated mice had significantly lower sucrose preference (anhedonia) and longer forced-swim immobility (behavioral despair), both hallmarks of depression. SRT1720 pre-treatment significantly reversed both measures. A complementary experiment using the SIRT1 inhibitor Ex527 confirmed that blocking SIRT1 alone was sufficient to induce depressive-like phenotypes, underscoring the causal role of SIRT1 activity.

Transmission electron microscopy of hippocampal tissue revealed that LPS caused nuclear chromatin condensation, swollen mitochondria with disrupted cristae, and a reduction in autophagosome number—signs of impaired mitophagy. SRT1720 markedly attenuated these structural abnormalities and substantially increased hippocampal autophagosomes. Western blotting confirmed elevated LC3II (a canonical autophagosome marker) and Parkin (the E3 ubiquitin ligase central to the PINK1/Parkin mitophagy pathway) in SRT1720-treated mice compared to LPS-only animals.

In vitro validation using LPS-challenged HT-22 hippocampal neurons showed that SRT1720 (10 µM) restored mitochondrial membrane potential assessed by JC-1 staining, reduced intracellular ROS measured by DCFH-DA, and recovered ATP production—collectively indicating rescued mitochondrial function. Protein analysis mirrored the in vivo findings, with increased LC3II and Parkin in SRT1720-treated cells, supporting a Parkin-dependent mitophagy mechanism as the key mediator of SIRT1's protective effects.

Taken together, these results suggest a mechanistic chain: SIRT1 activation → upregulation of Parkin → enhanced mitophagy → clearance of damaged mitochondria → reduced neuroinflammatory signaling and oxidative stress → alleviation of depressive behavior. Caveats include the use of a single, acute LPS model rather than chronic stress paradigms, an exclusively male mouse cohort, and the absence of genetic Parkin knockout experiments to formally prove pathway dependency. Nevertheless, the convergent in vivo and in vitro data make a compelling case for SIRT1-driven mitophagy as a tractable target in depression neurobiology.