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Altered NAD⁺ metabolism regulates SIRT2 activation in the cytosolic pool of sPD cells. a, b Representative immunoblot for SIRT2 cellular sub-compartmentalization in cytosol-, mitochondria-, nuclei-, and cystoskeleton-enriched fractions (a). Densitometric analysis of the levels of SIRT2 normalized against each fraction corresponding loading control to confirm equal protein loading and fraction purity. Values are mean ± S.E.M. (n = 7) (b). c ,d Representative immunoblot for acetylated-α-tubulin levels in cytosol-enriched fractions (c). Densitometric analysis of the levels of acetylated-α-tubulin. Values are mean ± S.E.M. (n = 4, *p < 0.05 versus CT cells). The blots were re-probed for α-tubulin and GAPDH to confirm equal protein loading (d). e, f Representative immunoblot for acetylated-α-tubulin levels in whole cellular extracts in presence or absence of lactate and sodium pyruvate (Lact/Pyr). The blots were re-probed for α-tubulin and GAPDH to confirm equal protein loading. Values are mean ± S.E.M. (n = 3, **p < 0.01 versus untreated CT cells, ###p < 0.001 versus untreated sPD cells) (f)
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Alterations in microtubule-dependent transport, mitochondrial dysfunction, and autophagic pathology are involved in neurodegeneration observed in sporadic Parkinson’s disease. However, the mechanistic link connecting these events remains elusive. We observed that NAD⁺ metabolism is altered in sporadic Parkinson’s disease patient-derived cells, whic...
Citations
... All this evidence suggests that SIRT2 could be playing an important role in this disease. In this sense, several studies have demonstrated that SIRT2 deletion or inhibition showed neuroprotective effects in rotenone and MPTP-induced animal models of PD [76,78,[80][81][82]. Moreover, it has been recently demonstrated that α-synuclein is a substrate of the deacetylase activity of SIRT2. ...
... Thus, in this scenario, its pharmacological inhibition is proposed as a neuroprotective strategy against aging and neurodegenerative diseases associated with it. Indeed, SIRT2 pharmacological inhibition has been proven to be effective in different models of HD [91,93], PD [81,[83][84][85], and AD [65,[71][72][73]. However, in our opinion, these results should be analyzed critically before any clinical attempt. ...
Sirtuin 2 (SIRT2), one of the seven members of the sirtuin family, has emerged as a potential regulator of aging and age-related pathologies since several studies have demonstrated that it shows age-related changes in humans and different animal models. A detailed analysis of the relevant works published to date addressing this topic shows that the changes that occur in SIRT2 with aging seem to be opposite in the brain and in the periphery. On the one hand, aging induces an increase in SIRT2 levels in the brain, which supports the notion that its pharmacological inhibition is beneficial in different neurodegenerative diseases. However, on the other hand, in the periphery, SIRT2 levels are reduced with aging while keeping its expression is protective against age-related peripheral inflammation, insulin resistance, and cardiovascular diseases. Thus, systemic administration of any known modulator of this enzyme would have conflicting outcomes. This review summarizes the currently available information on changes in SIRT2 expression in aging and the underlying mechanisms affected, with the aim of providing evidence to determine whether its pharmacological modulation could be an effective and safe pharmacological strategy for the treatment of age-related diseases.
... Sirtuins are a group of nicotinamide adenine dinucleotide (NAD + )-dependent protein deacetylase that use NAD + as a cofactor to remove an acetyl or other acyl group from the lysine residue of various substrates [1,2]. Among the seven human sirtuins (SIRT1-SIRT7), SIRT2 is the only one that mainly resides in the cytoplasm; however, it can be localized to the nucleus [3] and can also be detected in the mitochondria [4,5]. SIRT2 is implicated in different human diseases, including neurodegenerative diseases, cancer, and infections [6]. ...
SIRT2 is a member of NAD⁺-dependent sirtuins and its inhibition has been proposed as a promising therapeutic approach for treating human diseases, including neurodegenerative diseases, cancer, and infections. Expanding SIRT2 inhibitors based on the 3-aminobenzyloxy nicotinamide core structure, we have synthesized and evaluated constrained analogs and selected stereoisomers. Our structure-activity relationship (SAR) study has revealed that 2,3-constrained (S)-isomers possess enhanced in vitro enzymatic inhibitory activity against SIRT2 and retain excellent selectivity over SIRT1 and SIRT3, provided that a suitable ring A is used. This current study further explores SIRT2 inhibitors based on the 3-aminobenzyloxy nicotinamide scaffold and contributes to the discovery of potent, selective SIRT2 inhibitors that have been actively pursued for their potential therapeutic applications.
... Sirtuins (NAD-dependent histone deacetylases) are involved in aging and longevity. Mechanistically, altered NAD+ metabolism in patient-derived cells contributes to Sirtuin2 activation and ensuing a reduction in the acetylated from of α-tubulin levels [25]. Aberrant mitochondrial biogenesis causes an increasing loss of dopamine neurons and motor impairments in Drosophila models of PINK1 or parkin insufficiency. ...
Neurodegeneration is an age-dependent progressive phenomenon with no defined cause. Aging is the main risk factor for neurodegenerative diseases. During aging, activated microglia undergo phenotypic alterations that can lead to neuroinflammation, which is a well-accepted event in the pathogenesis of neurodegenerative diseases. Several common mechanisms are shared by genetically or pathologically distinct neurodegenerative diseases, such as excitotoxicity, mitochondrial deficits and oxidative stress, protein misfolding and translational dysfunction, autophagy and microglia activation. Progressive loss of the neuronal population due to increased oxidative stress leads to neurodegenerative diseases, mostly due to the accumulation of dysfunctional mitochondria. Mitochondrial dysfunction and excessive neuroinflammatory responses are both sufficient to induce pathology in age-dependent neurodegeneration. Therefore, mitochondrial quality control is a key determinant for the health and survival of neuronal cells in the brain. Research has been primarily focused to demonstrate the significance of neuronal mitochondrial health, despite the important contributions of non-neuronal cells that constitute a significant portion of the brain volume. Moreover, mitochondrial morphology and function are distinctly diverse in different tissues; however, little is known about their molecular diversity among cell types. Mitochondrial dynamics and quality in different cell types markedly decide the fate of overall brain health; therefore, it is not justifiable to overlook non-neuronal cells and their significant and active contribution in facilitating overall neuronal health. In this review article, we aim to discuss the mitochondrial quality control of different cell types in the brain and how important and remarkable the diversity and highly synchronized connecting property of non-neuronal cells are in keeping the neurons healthy to control neurodegeneration.
... Firstly, it is the sirtuin with the highest expression in the brain (Jayasena et al., 2016), although it is also expressed in a wide range of tissues and organs including the adipose tissue, muscle, liver, heart, kidney, and macrophages (Wang et al., 2007;Maxwell et al., 2011). Moreover, within the cell, it is the only member of the family mainly located in the cytoplasm (Jayasena et al., 2016) with the ability to translocate to the nucleus (North et al., 2003) and it is also found in the mitochondria (Liu et al., 2017;Esteves et al., 2018). Related to brain cells, it is most abundant in oligodendrocytes and microglia, but its expression is also important in neurons and astrocytes (Jayasena et al., 2016). ...
Alzheimer's disease is the most common cause of dementia globally with an increasing incidence over the years, bringing a heavy burden to individuals and society due to the lack of an effective treatment. In this context, sirtuin 2, the sirtuin with the highest expression in the brain, has emerged as a potential therapeutic target for neurodegenerative diseases. This review summarizes and discusses the complex roles of sirtuin 2 in different molecular mechanisms involved in Alzheimer's disease such as amyloid and tau pathology, microtubule stability, neuroinflammation, myelin formation, autophagy, and oxidative stress. The role of sirtuin 2 in all these processes highlights its potential implication in the etiology and development of Alzheimer's disease. However, its presence in different cell types and its enormous variety of substrates leads to apparently contradictory conclusions when it comes to understanding its specific functions. Further studies in sirtuin 2 research with selective sirtuin 2 modulators targeting specific sirtuin 2 substrates are necessary to clarify its specific functions under different conditions and to validate it as a novel pharmacological target. This will contribute to the development of new treatment strategies, not only for Alzheimer's disease but also for other neurodegenerative diseases.
... Altered NAD + metabolism observed in sporadic PD patientderived cells results in the activation of SIRT2 which subsequently reduces the level of acetylated tubulin and causes an imbalance in the trafficking and clearance of misfolded proteins, impairing MT assembly and the neuronal autophagic flux. Knockout of SIRT2 in these cells reverses the conditions and promotes neuronal survival [241]. The compound ICL-SIRT078 rescues the lactacystin-induced N27 cell lines from neuronal death by inducing tubulin acetylation and FOXO3a accumulation [183]. ...
The inter-neuronal communication occurring in extensively branched neuronal cells is achieved primarily through the microtubule (MT)-mediated axonal transport system. This mechanistically regulated system delivers cargos (proteins, mRNAs and organelles such as mitochondria) back and forth from the soma to the synapse. Motor proteins like kinesins and dynein mechanistically regulate polarized anterograde (from the soma to the synapse) and retrograde (from the synapse to the soma) commute of the cargos, respectively. Proficient axonal transport of such cargos is achieved by altering the microtubule stability via post-translational modifications (PTMs) of α- and β-tubulin heterodimers, core components constructing the MTs. Occurring within the lumen of MTs, K40 acetylation of α-tubulin via α-tubulin acetyl transferase and its subsequent deacetylation by HDAC6 and SIRT2 are widely scrutinized PTMs that make the MTs highly flexible, which in turn promotes their lifespan. The movement of various motor proteins, including kinesin-1 (responsible for axonal mitochondrial commute), is enhanced by this PTM, and dyshomeostasis of neuronal MT acetylation has been observed in a variety of neurodegenerative conditions, including Alzheimer’s disease and Parkinson’s disease (PD). PD is the second most common neurodegenerative condition and is closely associated with impaired MT dynamics and deregulated tubulin acetylation levels. Although the relationship between status of MT acetylation and progression of PD pathogenesis has become a chicken-and-egg question, our review aims to provide insights into the MT-mediated axonal commute of mitochondria and dyshomeostasis of MT acetylation in PD. The enzymatic regulators of MT acetylation along with their synthetic modulators have also been briefly explored. Moving towards a tubulin-based therapy that enhances MT acetylation could serve as a disease-modifying treatment in neurological conditions that lack it.
Graphical abstract
... Accumulating evidence leads to the hypothesis that the activation of innate immunity in dopaminergic neurons, through the exposure to DAMPs originating from mitochondrial dysfunction, bacteria, or even their metabolites targeting the mitochondria, could promote low-grade inflammation [135]. The mitochondrial network was found to be highly fragmented in cellular and animal models of PD [147], which is a pre-requisite for the selective degradation by mitophagy [147,148]. It was demonstrated that cardiolipin exposure, as a result of mitochondrial fission, is an important intervenient in the disposal of dysfunctional mitochondria [149]. ...
Parkinson’s Disease (PD), the second most common neurodegenerative disorder, is characterised by the severe loss of dopaminergic neurons in the Substantia Nigra pars compacta (SNpc) and by the presence of Lewy bodies. PD is diagnosed upon the onset of motor symptoms, such as bradykinesia, resting tremor, rigidity, and postural instability. It is currently accepted that motor symptoms are preceded by non-motor features, such as gastrointestinal dysfunction. In fact, it has been proposed that PD might start in the gut and spread to the central nervous system. Growing evidence reports that the gut microbiota, which has been found to be altered in PD patients, influences the function of the central and enteric nervous systems. Altered expression of microRNAs (miRNAs) in PD patients has also been reported, many of which regulate key pathological mechanisms involved in PD pathogenesis, such as mitochondrial dysfunction and immunity. It remains unknown how gut microbiota regulates brain function; however, miRNAs have been highlighted as important players. Remarkably, numerous studies have depicted the ability of miRNAs to modulate and be regulated by the host’s gut microbiota. In this review, we summarize the experimental and clinical studies implicating mitochondrial dysfunction and immunity in PD. Moreover, we gather recent data on miRNA involvement in these two processes. Ultimately, we discuss the reciprocal crosstalk between gut microbiota and miRNAs. Studying the bidirectional interaction of gut microbiome–miRNA might elucidate the aetiology and pathogenesis of gut-first PD, which could lead to the application of miRNAs as potential biomarkers or therapeutical targets for PD.
... 461 In a cellular model of PD patients, selective inhibition of SIRT2 increases tubulin acetylation and improves microtubule-mediated transport. 462 Moreover, SIRT2 inhibitors such as AGK2, AK-7, and AK1 have been demonstrated to decrease neuroinflammation and cytotoxicity induced by toxins or mutant protein aggregation. 463 Additionally, the HDAC6 inhibitor tubastatin A, which TA B L E 3 Representative acetylation substrates and their functions in health and diseases. ...
Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.
... However, we observed a decreased turnover of dysfunctional mitochondria in LPS-exposed neurons. It is well established that intracellular trafficking and autophagic turnover maintenance are highly dependent on mitochondrial function [45]. Interestingly, our data suggests that LPS by impairing mitochondrial function leads to the disruption of microtubule-dependent trafficking which ultimately affects macroautophagy. ...
... This was also observed in cells without functional mitochondria (NT2 Rho0). Several reports from our group have consistently reported that hybrid cells harboring PD patient mitochondria recapitulate several pathogenic features observed in PD subject brains including the accumulation of dysfunctional mitochondria and a-syn oligomers [45,53]. Importantly, in both PD cybrids and NT2 Rho0 cells LPS did not contributed to a further increase in a-syn oligomerization. ...
Sporadic Parkinson's disease (sPD) is a complex multifactorial disorder which etiology remains elusive. Several mechanisms have been described to contribute to PD development namely mitochondrial dysfunction, activation of inflammatory pathways and the deposition of unfolded proteins such as α-synuclein. Our work shows for the first time that lipopolysaccharide (LPS)-induced activation of innate immunity requires a functional mitochondria and mimics PD pathology in cells. We found in primary mesencephalic neurons that LPS targeted the mitochondria and activated neuronal innate immune responses, which culminated with α-synuclein oligomerization. Moreover, in cybrid cell lines repopulated with mtDNA from sPD subjects with inherent mitochondrial dysfunction and NT2-Rho0 obtained by long-term ethidium bromide exposure, and so without a functional mitochondrial, LPS was not able to further activate innate immunity or increase α-synuclein aggregation. Herein, we showed that mesencephalic neurons are able to activate innate immunity after LPS exposure and this pathway is dependent on mitochondria. Moreover, we disclose that α-synuclein over production is an innate immune response. Our data indicate that mitochondria provide the base for innate immunity activation in idiopathic PD.
... Sirtuins (SIRT, silent mating type information regulation 2 homolog in yeast) are NAD-dependent histone deacetylases reported to be involved in aging and longevity. Mechanistically, NAD+ metabolism is altered in sporadic PD patient-derived cells, which contributes to Sirtuin-2 activation and subsequent decrease in acetylated-α-tubulin levels [49]. PD-associated VPS35 (Vacuolar protein sorting ortholog 35) mutations show mitochondrial fragmentation and cell death in cultured neurons in vitro, in mouse substantia nigra neurons in vivo and in human fibroblasts from an individual with PD, who has the VPS35(D620N) mutation [50]. ...
Neurodegeneration is an age-dependent progressive phenomenon with no defined cause. Aging is the main risk factor for neurodegenerative diseases. During aging, activated microglia undergoes phenotypic alterations that can lead to neuroinflammation, which is well accepted event in the pathogenesis of neurodegenerative diseases. Several common mechanisms are shared by genetically or pathologically distinct neurodegenerative diseases, such as excitotoxicity, mitochondrial deficits and oxidative stress, protein misfolding and translational dysfunction, autophagy and microglia activation. Progressive loss of neuronal population due to increased oxidative stress leads to neurodegenerative diseases mostly due to the accumulation of dysfunctional mitochondria. Mitochondrial dysfunction and excessive neuroinflammatory responses are both sufficient to induce pathology in age-dependent neurodegeneration. Therefore, mitochondrial quality control is key determinant for the health and survival of neuronal cells in the brain. Research has been primarily focused to demonstrate the significance of neuronal mitochondrial health, despite the important contributions of non-neuronal cells that constitutes significant portion of the brain volume. Moreover, mitochondrial morphology and function are distinctly diverse in different tissues; however, little is known about their molecular diversity among cell types. Mitochondrial dynamics and quality in different cell types markedly decides the fate of overall brain health, therefore it is not justifiable to overlook non-neuronal cells and their significant and active contribution in facilitating overall neuronal health. In this review article, we aim to discuss the mitochondrial quality control of different cell types in the brain and how important and remarkable is the diversity and highly synchronized connecting property of non-neuronal cells in keeping the neurons healthy to control neurodegeneration.
... Our data show that despite the fragmentation of the mitochondrial network after bacteria-induced innate immunity activation, mitophagy is not functioning properly to avoid further activation of NLRP3 inflammasome. Previous data in PD models clearly show that mitochondrial dysfunction impairs mitophagy due to altered microtubule-dependent traffic [13,42,66]. Chung and coworkers showed that neuronal activation of TLR4 by activated microglia led to neuronal autophagy impairment and α-Syn aggregate accumulation [67]. ...
... Western blotting was performed as previously described in [13]. Samples were diluted in 6× sample buffer (4× Tris-Cl/SDS, pH 6.8, 30% glycerol, 10% SDS, 0.6 M DTT, 0.012% bromophenol blue) and boiled at 95 • C for 5 min. ...
Mitochondria play a key role in regulating host metabolism, immunity and cellular homeostasis. Remarkably, these organelles are proposed to have evolved from an endosymbiotic association between an alphaproteobacterium and a primitive eukaryotic host cell or an archaeon. This crucial event determined that human cell mitochondria share some features with bacteria, namely cardiolipin, N-formyl peptides, mtDNA and transcription factor A, that can act as mitochondrial-derived damage-associated molecular patterns (DAMPs). The impact of extracellular bacteria on the host act largely through the modulation of mitochondrial activities, and often mitochondria are themselves immunogenic organelles that can trigger protective mechanisms through DAMPs mobilization. In this work, we demonstrate that mesencephalic neurons exposed to an environmental alphaproteobacterium activate innate immunity through toll-like receptor 4 and Nod-like receptor 3. Moreover, we show that mesencephalic neurons increase the expression and aggregation of alpha-synuclein that interacts with mitochondria, leading to their dysfunction. Mitochondrial dynamic alterations also affect mitophagy which favors a positive feedback loop on innate immunity signaling. Our results help to elucidate how bacteria and neuronal mitochondria interact and trigger neuronal damage and neuroinflammation and allow us to discuss the role of bacterial-derived pathogen-associated molecular patterns (PAMPs) in Parkinson’s disease etiology.
