Cerebellar Predominant Increase in mRNA Expression Levels of Sirt1 and Sirt3 Isoforms in a Transgenic Mouse Model of Huntington's Disease

Interaction between resveratrol and SIRT1: role in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, pose significant health challenges and economic burdens worldwide. Recent studies have emphasized the potential therapeutic value of activating silent information regulator-1 (SIRT1) in treating these conditions. Resveratrol, a compound known for its ability to potently activate SIRT1, has demonstrated promising neuroprotective effects by targeting the underlying mechanisms of neurodegeneration. In this review, we delve into the crucial role of resveratrol-mediated SIRT1 upregulation in improving neurodegenerative diseases. The role of the activation of SIRT1 by resveratrol was reviewed. Moreover, network pharmacology was used to elucidate the possible mechanisms of resveratrol in these diseases. Activation of SIRT1 by resveratrol had positive effects on neuronal function and survival and alleviated the hallmark features of these diseases, such as protein aggregation, oxidative stress, neuroinflammation, and mitochondrial dysfunction. In terms of network pharmacology, the signaling pathways by which resveratrol protects against different neurodegenerative diseases were slightly different. Although the precise mechanisms underlying the neuroprotective effects of resveratrol and SIRT1 activation remain under investigation, these findings offer valuable insights into potential therapeutic strategies for neurodegenerative diseases.

Effect of 3-nitropropionic acid on sirtuin gene expression in Sirt3 deficient mice

Huntington's disease (HD) is an autosomal inherited progressive neurodegenerative disorder which is caused by the CAG trinucleotide repeat in the huntingtin gene. The mutation induces mitochondrial dysfunction in neurons, which leads to striatal neuronal loss. The efficacy of the available therapies is limited, thus acquisition of more data about the pathomechanism of HD and development of new strategies is urgent. Sirtuins (Sirt1-7) belong to the histone deacetylase family, and interestingly they have been associated with HD, however, their role in HD is still not fully understood. To clarify the role of sirtuins in HD, we utilized a 3-nitropropionic acid (3-NP) induced HD model and assessed alterations in gene expression using RT-PCR. Moreover, we studied the extension of neurodegeneration in the striatum, and behavioural changes. Furthermore, we involved Sirt3 knockout (Sirt3KO) mice to investigate the impact of Sirt3 deficiency in the expression of the other sirtuins. Our results showed that with 3-NP treatment, the mRNA level of Sirt2,5,7 changed significantly in wild-type (WT) mice, whereas in Sirt3KO animals there was no change. Interestingly, Sirt3 deficiency did not exacerbate 3-NP-mediated striatal neuronal loss, while Sirt3KO animals showed higher mortality than WT littermates. However, the absence of Sirt3 did not affect the behaviour of animals. Finally, we demonstrated that the changes in the expression of sirtuins are age- and sex- dependent. According to our findings, there is evidence that Sirt3 has a major impact on the regulation of other sirtuin isoforms, survival and neuroprotection. However, this neuroprotective effect does not manifest in the behaviour.

Targeting Mitochondrial Sirtuins in Age-Related Neurodegenerative Diseases and Fibrosis

Aging is a natural and complex biological process that is associated with widespread functional declines in numerous physiological processes, terminally affecting multiple organs and tissues. Fibrosis and neurodegenerative diseases (NDs) often occur with aging, imposing large burdens on public health worldwide, and there are currently no effective treatment strategies for these diseases. Mitochondrial sirtuins (SIRT3-5), which are members of the sirtuin family of NAD+-dependent deacylases and ADP-ribosyltransferases, are capable of regulating mitochondrial function by modifying mitochondrial proteins that participate in the regulation of cell survival under various physiological and pathological conditions. A growing body of evidence has revealed that SIRT3-5 exert protective effects against fibrosis in multiple organs and tissues, including the heart, liver, and kidney. SIRT3-5 are also involved in multiple age-related NDs, including Alzheimer's disease, Parkinson's disease, and Huntington's disease. Furthermore, SIRT3-5 have been noted as promising targets for antifibrotic therapies and the treatment of NDs. This review systematically highlights recent advances in knowledge regarding the role of SIRT3-5 in fibrosis and NDs and discusses SIRT3-5 as therapeutic targets for NDs and fibrosis.

Role of SIRT3 in mitochondrial biology and its therapeutic implications in neurodegenerative disorders

Sirtuin 3 (SIRT3), a mitochondrial deacetylase expressed preferentially in high-metabolic-demand tissues including the brain, requires NAD⁺ as a cofactor for catalytic activity. It regulates various processes such as energy homeostasis, redox balance, mitochondrial quality control, mitochondrial unfolded protein response (UPRmt), biogenesis, dynamics and mitophagy by altering protein acetylation status. Reduced SIRT3 expression or activity causes hyperacetylation of hundreds of mitochondrial proteins, which has been linked with neurological abnormalities, neuro-excitotoxicity and neuronal cell death. A body of evidence has suggested, SIRT3 activation as a potential therapeutic modality for age-related brain abnormalities and neurodegenerative disorders.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

Progressive Mitochondrial Dysfunction of Striatal Synapses in R6/2 Mouse Model of Huntington's Disease

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disorder characterized by synaptic dysfunction and loss of white matter volume especially in the striatum of the basal ganglia and to a lesser extent in the cerebral cortex. Studies investigating heterogeneity between synaptic and non-synaptic mitochondria have revealed a pronounced vulnerability of synaptic mitochondria, which may lead to synaptic dysfunction and loss.

OBJECTIVE

As mitochondrial dysfunction is a hallmark of HD pathogenesis, we investigated synaptic mitochondrial function from striatum and cortex of the transgenic R6/2 mouse model of HD.

METHODS

We assessed mitochondrial volume, ROS production, and antioxidant levels as well as mitochondrial respiration at different pathological stages.

RESULTS

Our results reveal that striatal synaptic mitochondria are more severely affected by HD pathology than those of the cortex. Striatal synaptosomes of R6/2 mice displayed a reduction in mitochondrial mass coinciding with increased ROS production and antioxidants levels indicating prolonged oxidative stress. Furthermore, synaptosomal oxygen consumption rates were significantly increased during depolarizing conditions, which was accompanied by a marked increase in mitochondrial proton leak of the striatal synaptosomes, indicating synaptic mitochondrial stress.

CONCLUSION

Overall, our study provides new insight into the gradual changes of synaptic mitochondrial function in HD and suggests compensatory mitochondrial actions to maintain energy production in the HD brain, thereby supporting that mitochondrial dysfunction do indeed play a central role in early disease progression of HD.