The Role Of Sirt1 In The Metabolic And Psychiatric Disorder Anorexia Nervosa & Investigating Proteostasis Renewal In The Immortal Germline
Aging leads to multiple diseases and eventually death due to a decline in molecular, cellular, and systemic processes. One contributing factor to aging is deregulated nutrient sensing, which is crucial for cellular metabolism. SIRT1 plays an important role in metabolism and brain function, but its expression decreases with age. Upregulating SIRT1 has been suggested as a potential anti-aging therapeutic. However, recent studies have shown potential side effects of increasing SIRT1 expression, including heightened anxiety, hyperactivity, and addiction predisposition. Notably, these side effects resemble those commonly observed in the metabolic and psychiatric disorder Anorexia Nervosa (AN). Therefore, we aimed to determine whether SIRT1 is involved in AN. We exposed brain-specific (BS) knockout (BSKO) and overexpressing (BSOX) SIRT1 mice to an activity-based anorexia (ABA) model of AN. BSOX mice were more susceptible to ABA, while BSKO mice were less so. Given the extensive research on SIRT1, multiple small molecules are readily available for potential therapeutic experiments, allowing for prompt testing both an inhibitor, Selisistat, and an activator, SRT1720. Our findings indicate that Selisistat provided protection from ABA, whereas SRT1720 exacerbated ABA phenotypes. Research from our group and others suggests that SIRT1 upregulates Mao-A and Foxo3a, leading to decreased serotonin levels, increased anxiety, hyperactivity, and addiction. We further propose that SIRT1 inhibits Grin2a, further contributing to increased anxiety and hyperactivity. Overall, our results suggest that inhibiting SIRT1 with Selisistat may offer a potential therapeutic approach for treating AN. Additionally, our work continues to encourage mental health monitoring when modulating SIRT1 levels either for anti-aging purposes or as a therapeutic for specific diseases. One other major contributing factor to aging is the loss of proteostasis, impairing the cell’s ability to function and leading to accumulation of misfolded proteins and protein aggregates. However, this loss of proteostasis is not passed down through generations; if it were, species would become extinct. This phenomenon, known as germline immortality, suggests that the germline is either shielded from damage or actively clears it to prevent transmission from one generation to the next. In examining the proteome, we observed that mouse oocytes accumulate aggregated proteins as they age. Consequently, we investigated whether oocytes clear these aggregates. Initially, we examined both the oocytes and their polar bodies, finding that the oocytes did not transfer the aggregates to the polar bodies for degradation. Subsequently, we stained oocytes at the germinal vesicle (GV) stage, during GV breakdown, and in meiosis II-arrested oocytes. Our findings revealed that while the number of aggregates decreased in older oocytes, the total volume remained consistent, indicating that the smaller aggregates were combining to form larger aggregates. Furthermore, despite the aggregates not being degraded, they colocalized with autophagosome membrane protein LC3B and lysosome membrane protein LAMP1. This suggests that the aggregates are being primed for degradation following meiosis I reactivation. Interestingly, these observations contrast with the degradation patterns seen in maturing oocytes of C. elegans, suggesting a unique timeline in mouse oocytes where degradation preparations occur post-fertilization. Nonetheless, our research, alongside similar studies, emphasizes the potential of meiotic cells as instrumental models for understanding proteostasis restoration in aged cells.
Robinette TM, Nicholatos JW, Francisco AB, Brooks KE, Diao RY, Sorbi S, Ricca V, Nacmias B, Brieño-Enríquez MA, Libert S. SIRT1 accelerates the progression of activity-based anorexia. Nat Commun. 2020 Jun 4;11(1):2814. doi: 10.1038/s41467-020-16348-9. PMID: 32499508; PMCID: PMC7272424.