Relevance and application of sirtuin 3-activated mitophagy in gastric cancer treatment

Abstract

Sirtuin 3 (SIRT3) is a primary mitochondrial deacetylase. Studies have confirmed that it directly activates mitophagy by modulating mitochondrial protein acetylation. As a key homeostatic mechanism, mitophagy activation alleviates oxidative stress-induced imbalance between cell proliferation and apoptosis, corrects stress-driven mitochondrial metabolic dysfunction, and thus inhibits excessive tumor growth, exerting significant antitumor effects. These functions establish SIRT3 as a key target for regulating mitophagy and cancer therapy. Clinically, strategies centered on its precise regulation may offer a novel direction for gastric cancer (GC) prevention and treatment, with selective activation remaining a critical challenge. SIRT3 could also serve as an auxiliary indicator in clinical guidelines for assessing tumor progression. Given this potential, this mini-review systematically examines SIRT3’s mechanisms in regulating mitophagy, its role in GC pathogenesis, and translational prospects for targeting SIRT3 in GC management.

Key Words: Sirtuin 3; Gastric cancer; Mitochondrial function; Mitophagy; Oxidative stress; Antitumor

Core Tip: Sirtuin 3 (SIRT3), a mitochondrial NAD⁺-dependent deacetylase, regulates mitophagy via protein acetylation and signaling pathways. Downregulated in gastric cancer (GC), its low expression links to poor prognosis, deeper invasion, and reduced differentiation. SIRT3 enhances mitophagy to alleviate oxidative stress, correct mitochondrial dysfunction, and inhibit GC. Preclinical studies show it synergizes with therapies, boosting efficacy and reducing toxicity. This mini-review covers its mechanisms, therapeutic potential, and prospects for activator/delivery system development.

INTRODUCTION

Gastric cancer (GC) is a digestive tract malignancy arising from gastric mucosal epithelial tissue. Its development involves the interactions of multiple factors and a multistage pathological progression. Epidemiological studies identify persistent Helicobacter pylori infection as the primary cause, with bile reflux, age, genetics, obesity, smoking, and alcohol consumption forming a complex pathogenic network[1]. Global cancer statistics rank GC fifth in both incidence and mortality[2]. Despite advances in diagnosis and treatment, the five-year survival rate for advanced GC remains below 20%[3]. Thus, deeper research into its molecular mechanisms and improved prevention/treatment strategies are critical to curb progression and enhance patient quality of life.

As the core organelle of energy metabolism in eukaryotic cells, mitochondria participate in key physiological processes such as adenosine triphosphate (ATP) synthesis, calcium ion homeostasis regulation, and programmed cell death signal transduction through the oxidative phosphorylation pathway. Their functional integrity is critical for determining cell fate[4,5]. Mitophagy, a highly conserved cellular quality control mechanism, selectively identifies and degrades dysfunctional mitochondria. This process effectively maintains intracellular homeostasis and mitigates organelle damage from various stressors[6]. Notably, in GC development, mitophagy plays a pivotal regulatory role: By clearing mitochondria with oxidative damage caused by excessive reactive oxygen species (ROS) accumulation, it inhibits the buildup of oncogenic mutations[7,8]. Given these molecular mechanisms, targeted regulation of key nodes in the mitochondrial quality control network holds promise as a novel strategy to reverse GC progression.

The sirtuin family, a group of highly conserved NAD⁺-dependent deacetylases, plays a central role in regulating metabolic homeostasis[9,10]. Among them, sirtuin 3 (SIRT3) – a key mitochondrial regulator – not only maintains mitochondrial energy metabolism balance but also modulates nuclear gene transcriptional activity via epigenetic modifications, exerting unique biological functions[11,12]. Recent studies show that dysregulated SIRT3 expression correlates closely with pathological processes in various solid tumors, including liver, gallbladder, ovarian, and colorectal cancers[13-16]. Notably, mitophagy is persistently suppressed during "inflammation-cancer transformation"[17], whereas SIRT3 can enhance mitophagy to clear damaged organelles, thereby mitigating oxidative stress[18]. Clinical evidence indicates that SIRT3 expression in GC tissues strongly correlates with better patient prognosis[19]. However, its functional targets and molecular regulatory networks remain incompletely understood. This mini-review systematically elaborates on the molecular pathways through which SIRT3 regulates mitophagy and its roles in GC prevention and treatment, aiming to provide a theoretical basis for developing novel therapies targeting the SIRT3 signaling axis.

BIOLOGICAL PROPERTIES OF SIRT3

Structure and function of SIRT3

SIRT3 shares structural similarities with other sirtuin family members, featuring a conserved enzymatic core composed of two domains: A large Rossmann-fold NAD⁺-binding domain and a catalytic zinc finger domain formed by helical bundles and zinc-binding motifs (Figure 1)[20]. As its name suggests, the NAD⁺-binding domain specifically binds the cofactor NAD⁺, with its conformational changes directly impacting enzymatic deacetylation activity[21]. The catalytic zinc finger structure stabilizes the active site by chelating zinc ions via cysteine and histidine residues, contributing to both substrate acetyl site recognition and deacetylation. The remaining portion of the enzymatic core contains SIRT3 substrate-binding sites[22]. Additionally, SIRT3 has variable N-terminal and C-terminal domains, which can modulate substrate binding specificity through conformational changes[23].

Figure 1 Structure of sirtuin 3. The conserved enzymatic core of sirtuin 3 comprises a Rossmann fold domain, a catalytic zinc finger motif, and a substrate-binding region.

SIRT3 engages in diverse physiological and pathological processes through deacetylation (Figure 2). For instance, SIRT3-mediated activation of acetyl-CoA synthetase 2 drives more acetyl-CoA into the tricarboxylic acid cycle, thereby sustaining redox balance[24]. It also regulates key mitochondrial metabolic processes – including fatty acid oxidation, oxidative phosphorylation, the urea cycle, and amino acid metabolism – making it a critical target for metabolic disease therapies[12,25]. In stress adaptation, SIRT3 maintains mitochondrial ROS homeostasis and mitigates oxidative damage by activating deacetylation of multiple antioxidant enzymes and regulating mitophagy[26,27]. This trait has made it a focus of research in aging, cancer, and neurological diseases.

Figure 2 Function of sirtuin 3 and its potential application in the prevention and treatment of cancer. AceCS2: Acetyl-CoA synthetase 2; ETC: Electron transport chain; REDOX: Oxidation/reduction; ROS: Reactive oxygen species; TCA: Tricarboxylic acid.

Role and regulatory mechanism of SIRT3

The deacetylation reaction of SIRT3 is completed through four consecutive steps. First, the acetylated protein binds to NAD⁺ at the enzyme's active site, triggering a conformational change that embeds the nicotinamide group into a hydrophobic pocket. Subsequently, the ribose C1 atom of NAD⁺ undergoes a nucleophilic attack by the carbonyl oxygen of the substrate, facilitating the transfer of the acetyl group to ADP-ribose and releasing nicotinamide. Next, catalyzed by the histidine residue (His224), the intermediate rearranges to form a bicyclic structure. Finally, this structure is hydrolyzed to generate deacetylated protein and 2'-O-acetyl-ADP-ribose. The entire process is strictly NAD⁺-dependent, achieving regulation of protein function through precise molecular recognition and catalysis (Figure 3)[22].

Figure 3 Sirtuin 3 modification deacetylates its substrate in an NAD⁺-dependent manner. His224: Histidine residue.

SIRT3 regulation operates through multiple dimensions, including transcriptional control, post-translational modifications, protein interaction networks, and responses to the metabolic microenvironment. Notably, under hypoxia, hypoxia-inducible factor-1α (HIF-1α) binds to the SIRT3 gene promoter, repressing its transcription. This reduces tricarboxylic acid cycle activity and enhances glycolysis, representing a key negative transcriptional regulatory mechanism (Figure 4A)[28]. Additionally, SUMOylation of SIRT3 inhibits its enzymatic activity[29]. In positive regulation (Figure 4B) transcription factors such as forkhead box protein O3a and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) bind to the SIRT3 promoter to drive its expression[18,30]. Moreover, AMP-activated protein kinase (AMPK) and SIRT3 form a positive feedback loop that mutually enhances their activity. The two also act synergistically on PGC-1α, with this three-component pathway serving as a classic driver of mitochondrial metabolism[31]. Finally, as a NAD⁺-dependent deacetylase, SIRT3 activity is governed by intracellular NAD⁺ levels. Thus, mechanisms regulating NAD⁺ dynamics – such as those involving nicotinamide phosphoribosyl transferase and nicotinamide mononucleotide – also influence SIRT3 function[32,33].

Figure 4 Conventional negative and positive regulatory mechanism of sirtuin 3. A: Conventional negative regulatory mechanism of sirtuin 3 (SIRT3). In the hypoxic microenvironment, hypoxia-inducible factor-1α (HIF-1α) selectively activates glycolysis-related enzymes and inhibits mitochondrial SIRT3 to block the tricarboxylic acid cycle – a hallmark of the classic "Warburg effect". This process drives local reactive oxygen species accumulation and amplifies inflammatory cascades, worsening hypoxia and creating a negative feedback loop targeting SIRT3. Notably, activating SIRT3 can suppress hypoxia-induced HIF-1α overexpression through specific mechanisms, thereby disrupting the sustained activation of this closed negative regulatory loop; B: Conventional positive regulatory mechanism of SIRT3. SIRT3-AMP-activated protein kinase-peroxisome proliferator-activated receptor γ coactivator 1α-SIRT3 positive feedback loop represents a key pathway for SIRT3's positive regulation. AMPK: AMP-activated protein kinase; ATP: Adenosine triphosphate; FoxO3a: Forkhead box protein O3a; HIF-1α: Hypoxia-inducible factor-1α; ROS: Reactive oxygen species; SIRT3: Sirtuin 3; SUMO: Small ubiquitin-related modifier; TCA: Tricarboxylic acid; PGC-1α: Peroxisome proliferator-activated receptor γ coactivator 1α.

INTERACTION BETWEEN SIRT3 AND MITOPHAGY

Mitophagy, the selective removal of damaged or dysfunctional mitochondria, is critical for maintaining cellular homeostasis[6]. SIRT3 influences mitophagy progression directly and indirectly by regulating the acetylation status of multiple key proteins and metabolic pathways. Its mechanisms of action are summarized below.

The direct regulatory mechanisms of SIRT3 on mitophagy

SIRT3 directly deacetylates autophagy-related proteins to enhance their functions. For example, it deacetylate the autophagy receptor BCL2-interacting protein 3 (BNIP3), strengthening its binding to microtubule-associated protein 1 light chain 3 (LC3). This boosts the efficiency of the non-ubiquitinated pathway and promotes encapsulation of damaged mitochondria by autophagosomes[34]. Additionally, SIRT3 activates antioxidant enzymes such as superoxide dismutase 2 (SOD2) and catalase, inhibiting excessive intracellular ROS accumulation. This maintains moderate ROS signaling to activate autophagy[35,36]. Finally, SIRT3 enhances electron transport chain efficiency by regulating mitochondrial metabolic enzyme activity[37], preserving intracellular ATP and NAD⁺ levels. This modulates the activity of other sirtuin family members and ROS production, creating favorable conditions for mitophagy initiation (Figure 5).

Figure 5 Mechanisms of sirtuin 3 regulation of mitophagy. AMPK: AMP-activated protein kinase; ATP: Adenosine triphosphate; BNIP3: BCL2-interacting protein 3; CAT: Catalase; LC-3: Light chain 3; mTOR: Mammalian target of rapamycin; OSCP: Oligomycin sensitivity conferral protein; PINK1: Phosphatase and tensin homolog-induced putative kinase 1; ROS: Reactive oxygen species; SIRT3: Sirtuin 3; SOD2: Superoxide dismutase 2; TCA: Tricarboxylic acid; PGC-1α: Peroxisome proliferator-activated receptor γ coactivator 1α.

Synergistic regulation of mitophagy by SIRT3 and other signaling pathways

SIRT3 coordinately regulates mitophagy by deacetylating key autophagy-related proteins. Among various autophagic signaling pathways, the phosphatase and tensin homolog-induced putative kinase 1 (PINK1)/Parkin pathway – core to ubiquitination-dependent mitophagy – is also modulated by SIRT3[38]. By maintaining mitochondrial metabolic balance, SIRT3 indirectly regulates changes in mitochondrial membrane potential[39], promoting increased expression of PINK1 on the outer mitochondrial membrane[40]. This activates E3 ubiquitin ligase activity, facilitating ubiquitination labeling of damaged mitochondria. Additionally, SIRT3 and AMPK act synergistically to promote AMPK phosphorylation and inhibit mechanistic target of rapamycin complex 1 (mTORC1) complex synthesis, thereby relieving mTORC1’s suppression of autophagy[41]. Furthermore, SIRT3-regulated PGC-1α can modulate expression of the autophagic receptor FUNDC1 through interaction with nuclear respiratory factor 1 (Figure 5)[42].

Expression level of SIRT3 in GC

Studies have shown that SIRT3 expression is significantly lower in GC tissues than in adjacent normal tissues[43], with its expression intensity dynamically and inversely correlated with tumor progression. For example, Yang et al[44] demonstrated via cohort analysis that GC invasion depth and clinical stage are significantly negatively associated with SIRT3 expression, suggesting SIRT3 may play a key role in inhibiting local tumor invasion. Further research indicates that low SIRT3 expression correlates closely with reduced tumor differentiation – poorly differentiated GCs exhibit more pronounced loss of SIRT3 protein[45]. Additionally, SIRT3 expression varies across GC subtypes: Its positive expression rate is significantly higher in intestinal-type GC than in diffuse adenocarcinoma. This may stem from SIRT3’s specific regulation of key glycolytic enzyme acetylation in intestinal-type GC, thereby driving the Warburg effect[46]. Most studies confirm that elevated SIRT3 expression inhibits GC cell proliferation[43,47-49]. In summary, loss of SIRT3 expression is not only a biomarker for GC malignant progression but also a potential therapeutic target.

SIRT3 regulates mitophagy in GC

Current global research on SIRT3’s role in GC remains relatively limited, and the following analysis draws primarily on existing literature. He et al[49] found that 5-fluorouracil (5-FU) treatment significantly upregulated SIRT3 expression in GC cells, accompanied by increased levels of autophagic activity markers BNIP3 and LC3. Conversely, inhibiting 5-FU-induced SIRT3 upregulation with 3-methyladenine indicated that SIRT3 is involved in autophagy in GC cells. Debsharma et al[47] further revealed that indomethacin downregulated SIRT3 in GC tissues, reducing PGC-1α and AMPK expression and disrupting the AMPK/SIRT3/PGC-1α feedback loop. This simultaneously inhibited two key autophagic regulatory pathways, further exacerbating cell apoptosis. Studies by Wang et al[43] and Ma et al[48] confirmed that upregulating SIRT3 significantly reduced Notch-1 expression in GC, thereby suppressing GC cell proliferation and invasion. Notably, prior research showed that Notch-1 overexpression inhibits mixed-lineage kinase 3 silencing-induced autophagy[50], suggesting SIRT3 may activate mitophagy by repressing Notch-1, thus delaying GC progression. Additionally, Lee et al[51] found that SIRT3 overexpression attenuated HIF-1α transcriptional activity. Given that stable HIF-1α expression primarily activates glycolysis-related enzymes while weakening its induction of the autophagic protein BNIP3[52], SIRT3 may promote autophagy in GC by inhibiting HIF-1α. Finally, Debsharma et al[47] observed that reduced SIRT3 expression in GC leads to SOD2 acetylation, inhibiting SOD2 activity, elevating intracellular ROS levels, and ultimately suppressing autophagy initiation. Collectively, these findings highlight multiple mechanisms through which SIRT3 regulates autophagy in GC.

POTENTIAL APPLICATION OF SIRT3 IN THE PREVENTION AND TREATMENT OF GC

As previously discussed, SIRT3 expression is significantly reduced in GC, and its low expression level is often closely associated with poor patient prognosis. SIRT3 regulates mitophagy through deacetylation, alleviating oxidative stress-induced cellular damage and enhancing cellular adaptability to environmental stress, thereby playing a critical role in inhibiting GC progression and improving patient outcomes. Therefore, the development of SIRT3-specific activators to enhance mitophagy and eliminate damaged mitochondria may provide novel strategies for the prevention of gastric precancerous lesions and early-stage GC, filling the research gap in this field.

Furthermore, SIRT3 demonstrates potential for combined use with chemotherapeutic and targeted drugs in cancer treatment. Studies by He et al[49] have shown that SIRT3 is involved in the mitophagy induced by 5-FU, suggesting that the combination of SIRT3 activators with 5-FU can synergistically enhance mitophagy and inhibit the progression of GC cells. Additionally, research indicates that upregulation of SIRT3 significantly enhances the sensitivity of tumor cells to platinum-based chemotherapeutic drugs (such as cisplatin and oxaliplatin)[53,54]. In addition, the SIRT3 activator nicotinamide riboside has been confirmed to enhance the anticancer activity of paclitaxel[55]. Notably, SIRT3-mediated mitophagy can also effectively reduce the cytotoxicity caused by paclitaxel and platinum-based chemotherapeutics[56,57], thereby improving the safety of treatment regimens. Based on existing research evidence, the combined use of SIRT3 agonists with conventional chemotherapeutic drugs may produce synergistic effects while reducing toxic and side effects. However, it is important to note that overexpression of SIRT3 may also lead to tumor resistance to 5-FU and platinum-based drugs[58,59]. Therefore, precise regulation of SIRT3 activator dosage is required in clinical applications, and the combined use of SIRT3 activity inhibitors may be considered when necessary to overcome chemoresistance.

In combination with targeted drugs, SIRT3 not only exhibits synergistic mechanisms similar to those with chemotherapeutic agents but also exerts unique regulatory functions on the action of targeted drugs. Specifically, SIRT3 directly participates in and influences the action of targeted drugs by regulating cellular signal transduction pathways, thereby enhancing therapeutic efficacy and optimizing treatment strategies. For example, studies have shown that SIRT3 can affect mitophagy and apoptosis by regulating the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin signaling pathway[58], a mechanism that is highly compatible with the therapeutic effects of epidermal growth factor receptor (EGFR) or anti-human EGFR2 targeted drugs[60,61]. Therefore, increasing the expression level of SIRT3 in GC may help enhance the therapeutic efficacy of targeted drugs, providing new potential strategies for targeted therapy of GC.

Given the close association between SIRT3 expression levels and GC prognosis as well as drug responsiveness, it can be incorporated into the overall efficacy evaluation system of tumor therapy to achieve more precise monitoring and regulation of treatment effects. By integrating the expression status and functional activity of SIRT3, it is expected to develop more precise individualized treatment plans for GC patients in the future, further improving clinical therapeutic outcomes (Figure 2).

DISCUSSION

Current research on SIRT3 in the field of GC prevention and treatment has the following limitations.

Incomplete molecular mechanism elucidation

The specific mechanisms of SIRT3 in GC have not been fully clarified, particularly the differences in its roles across different GC subtypes (such as intestinal-type and diffuse adenocarcinoma), which require further investigation.

Gaps in clinical translation evidence

Most current studies are limited to in vitro cell models and mouse xenograft experiments, lacking validation from multi-center, large-sample clinical cohort studies, thus hindering the translation of basic research into clinical applications.

Insufficient biosafety evaluation

As a core regulator of mitochondrial function, interventions targeting SIRT3 may trigger cascading physiological effects. Notably, while activating the mitophagy pathway to inhibit tumor cells, the potential damage of this process to normal gastric mucosal epithelial cells remains unclear. Developing more precise spatiotemporal regulation strategies is essential to balance efficacy and safety.

Lagging development of targeted drugs

Existing SIRT3 activators, largely designed around sirtuin family conserved domains, have poor selectivity[33]. Developing highly selective small-molecule activators targeting SIRT3's unique deacetylation domain is a key technical bottleneck. Moreover, low mitochondrial delivery efficiency, challenges in vivo efficacy validation, and lack of biomarkers also hinder development.

FUTURE RESEACH DIRECTIONS

In the field of GC prevention and treatment, future research directions targeting the mechanism of SIRT3-activated mitophagy can be explored in depth from the following dimensions.

Molecular mechanisms

Further clarification of the specific signaling pathways through which SIRT3 activates mitophagy in GC is needed to identify more potential regulatory targets. Investigation of the functional heterogeneity of SIRT3-mediated mitophagy across different molecular subtypes of GC, and clarification of the molecular basis of its interaction with the tumor microenvironment.

Clinical translation and safety

Through structure-based precision design and tumor microenvironment-responsive nano-delivery systems, GC-specific SIRT3 activators can be developed[62,63]. These molecules induce mitophagy in GC cells by activating SIRT3, while mitochondrial-targeting peptides enhance delivery efficiency and reduce damage to normal gastric mucosal epithelium[64]. Additionally, metabolomics can assist in efficacy evaluation, and novel biomarkers need to be developed to enable precise regulation of the therapeutic window. Construction of GC organoid models and genetically engineered mouse models to systematically evaluate the therapeutic window of SIRT3 activators and screen molecular markers for patients sensitive to SIRT3 activation.

Combination therapy optimization

Systematic exploration of the synergistic mechanisms between SIRT3-activated mitophagy and chemotherapeutic drugs (e.g., 5-FU, platinum compounds), targeted drugs (e.g., anti-HER2 antibodies, EGFR inhibitors), and immunotherapy, to define optimal administration sequences and dose combinations.

Development of intelligent delivery systems for dynamic regulation of SIRT3 activity, combined with real-time imaging monitoring technology, to precisely control the intensity of mitophagy and avoid chemotherapy resistance or normal tissue damage caused by excessive activation.

It is recommended that large-sample studies should be conducted to analyze the correlation between SIRT3 expression in serum/tissues and the occurrence/progression of GC, and construct a quantitative model by integrating clinical pathological features. Additionally, integrating SIRT3 with traditional markers to establish multi-dimensional diagnostic indicators can enhance the efficacy of early diagnosis and prognostic assessment for GC.

CONCLUSION

Given the high incidence and mortality of GC, elucidating its molecular mechanisms is crucial for improving prevention and treatment strategies. Oxidative stress persists throughout GC progression[65], positioning mitophagy as a key target to mitigate stress-induced cellular damage. Notably, mitophagy is progressively inhibited during GC development, underscoring the therapeutic potential of activating this pathway. As a critical regulator of mitophagy, SIRT3’s unique structural features enable its functional activation in the gastric microenvironment. It promotes mitophagy by modulating autophagic receptors, key proteins, and signaling pathways. Additionally, SIRT3’s role in regulating mitochondrial metabolism may enhance synergistic effects when combined with chemotherapeutics (e.g., 5-FU, platinum compounds) or targeted therapies, while reducing associated toxicities. Its strong correlation with GC prognosis also suggests utility in evaluating therapeutic efficacy.

SIRT3 offers distinct advantages over other targets: Unlike membrane receptor signaling cascades (e.g., EGFR, HER2) that rely on amplification, SIRT3 localizes directly to the mitochondrial matrix, enabling precise regulation of redox homeostasis. Moreover, recent studies indicate that coupling pH-sensitive nano-delivery systems with SIRT3 activators can adapt to the acidic microenvironment of GC tissues, enabling more precise targeted delivery than conventional therapies[64]. Furthermore, SIRT3 regulates mitophagy through multiple pathways, making it more effective in overcoming systemic tumor drug resistance compared to single-pathway interventions.

Future research should focus on three key areas: Deepening the mechanistic understanding of SIRT3 in GC, developing highly selective small-molecule activators with favorable safety profiles, and conducting large-scale randomized controlled trials or cohort studies to fully validate its potential in GC management.