Synergistic Autophagy-Related Mechanisms of Protection Against Brain Aging and AD: Cellular Pathways and Therapeutic Strategies

Abstract

Brain aging is driven by interconnected processes, including impaired autophagy, chronic inflammation, mitochondrial dysfunction, and cellular senescence, all of which contribute to neurovascular decline and neurodegenerative diseases such as Alzheimer's disease (AD). Targeting these mechanisms simultaneously offers a promising therapeutic approach. This review explores the rationale for combining metformin, benzimidazole derivatives, phosphodiesterase-5 (PDE5), and acetylsalicylic acid (ASA) as a multi-targeted strategy to restore proteostasis, reduce senescence-associated secretory phenotype (SASP) factors, and enhance mitochondrial and lysosomal function. Metformin activates AMP-activated protein kinase (AMPK) and promotes autophagy initiation and chaperone-mediated autophagy, whilst benzimidazole derivatives enhance lysosomal fusion through JIP4-TRPML1 pathways independently of mTOR signaling; and ASA augments autophagic flux while suppressing NF-κB-driven inflammation and promoting specialized pro-resolving mediator pathways. This combinatorial approach targets both upstream autophagy initiation and downstream autophagosome-lysosome fusion, while concurrently attenuating inflammation and cellular senescence. Patient stratification based on the biomarkers of autophagy impairment, inflammation, and metabolic dysfunction could optimize therapeutic responses. While this strategy shows strong preclinical promise, careful attention to timing, dosing, and cell-specific responses is crucial to maximize benefits and avoid adverse effects. Future studies integrating biomarker-guided precision medicine frameworks are essential to validate the potential of this therapeutic combination in preventing or slowing cognitive decline and promoting healthy brain aging.

Keywords: Alzheimer’s disease; acetylsalicylic acid; autophagy; benzimidazole; metformin; neurodegeneration.

Figure 1

Schematic illustration of rapamycin’s neuroprotective mechanisms in AD, highlighting its direct inhibition of mTORC1 (independent of AMPK), the induction of autophagy via ULK-1 activation, reduction in amyloid and tau pathology, and the modulation of microglial polarization. Abbreviations: mTORC1—mammalian target of rapamycin complex 1; ULK1—unc-51-like autophagy-activating kinases 1; Aβ—amyloid beta; AD—Alzheimer’s disease.

Figure 2

Metformin-mediated modulation of autophagy pathways: This diagram summarizes the key signaling mechanisms through which metformin modulates both macroautophagy and CMA. Metformin activates AMPK, leading to mTORC1 inhibition and the upregulation of ULK1/ATG13, thereby enhancing autophagic flux via LC3 and Beclin-1. Independently, it activates CMA through the TAK1–IKKα/β pathway and Hsc70 phosphorylation. Additional neuroprotective effects include Nrf2-mediated antioxidant defense and improved mitochondrial function via SIRT1. While microglial autophagy supports Aβ and tau clearance, AMPK activation in astrocytes may paradoxically reduce autophagy, highlighting cell-type specificity. Inhibition (red); activation (green). Abbreviations: mTOR—mammalian target of rapamycin; BDNF—brain-derived neurotrophic factor; Aβ—amyloid beta; AMPK—AMP-activated protein kinase; ULK1—Unc-51-like autophagy-activating kinases; SIRT-1—silent mating-type information regulation 2 homolog; APP—amyloid precursor protein; PSEN-1—presenilin-1; TAK1—transforming growth factor β-activated kinase 1; HSC70—Heat Shock Cognate protein 70; ATG13—autophagy-related protein 13; Iκκ—I kappa B kinase.

Figure 3

Schematic representation of the molecular pathways by which PDE5 inhibitors (sildenafil, tadalafil, mirodenafil) promote autophagy induction and neuroprotection. PDE5 inhibition increases cGMP levels, activating PKG and downstream CREB signaling, which upregulates autophagy-related proteins (LC3, Beclin-1, BDNF) and facilitates Aβ and tau clearance. The parallel modulation of the AMPK/mTOR and GSK-3/β-catenin pathways further enhances autophagy and reduces neurodegenerative protein accumulation. Abbreviations: LC3—microtubule-associated proteins 1A/1B light chain 3; mTOR—mammalian target of rapamycin; BDNF—brain-derived neurotrophic factor; Aβ—amyloid beta; AMPK—AMP-activated protein kinase; CREB—cAMP Response Element-Binding Protein; PKG—protein kinase G; ATP—adenosine tri-phosphate.

Figure 4

This diagram illustrates the mTOR-independent modulation of autophagy and cellular senescence by benzimidazole derivatives (e.g., FLBZ and albendazole). These compounds promote lysosomal clustering and autophagosome–lysosome fusion, facilitating the clearance of protein aggregates via AMPK and ULK-1 activation. Simultaneously, they reduce cellular senescence and SASP-driven neuroinflammation by suppressing key pro-inflammatory cytokines (TNF-α and IL-6), highlighting their therapeutic potential in neurodegenerative diseases. Abbreviations: mTOR—mammalian target of rapamycin; SASP—senescence-associated secretory phenotype; TNF-α—Tumor Necrosis Factor alpha; IL-6—Interleukin-6.

Figure 5

Schematic representation of the signaling pathways by which acetylsalicylic acid (ASA) modulates autophagy. ASA promotes the production of specialized pro-resolving mediators (SPMs), particularly RvD1, which enhances the expression of autophagy-related proteins LC3B and Beclin-1 while suppressing NLRP3 inflammasome and SASP via NF-κB inhibition. ASA also reduces COX-2-mediated neuroinflammation, indirectly modulating mTOR activity. Together, these pathways converge to activate autophagy and promote the clearance of pathological aggregates. Abbreviations: LC3B—microtubule-associated proteins 1A/1B light chain 3B; RvD1—resolvin D1; NF-κB—nuclear factor kappa B; COX-2—cyclooxygenase-2; mTOR—mammalian target of rapamycin; SASP—senescence-associated secretory phenotype.

Figure 6

This Venn diagram illustrates the interplay of major pharmacological agents and pathways involved in autophagic modulation, highlighting both shared and unique mechanisms. Rapamycin, positioned in the blue circle, activates autophagy through the inhibition of the mTOR pathway, a well-established negative regulator of autophagy. Metformin, within the yellow circle, promotes autophagy via AMPK activation, engaging ULK1 and initiating autophagosome formation independently of mTOR. The red circle contains ASA, which modulates autophagy and inflammation by inhibiting COX-2 and NF-κB signaling. PDE5 inhibitors appear in the purple circle, acting through the cGMP-PKG pathway to stimulate autophagy in an mTOR-independent manner. Benzimidazole compounds span both the red and purple circles, implicating them in COX-2/NF-κB and cGMP-mediated mechanisms, while also being associated with enhanced lysosomal degradation. Key autophagic markers (LC3 and p62) occupy central positions, reflecting their common regulation across these pathways. Beclin-1 and lysosomal clearance are indirectly linked to benzimidazoles via dotted lines, emphasizing their contribution to mTOR-independent autophagy. The convergence of diverse signaling networks on autophagic modulation can be seen, implicating multi-target agents in therapeutic strategies. Abbreviations: mTOR—mammalian target of rapamycin; ULK1—unc-51-like autophagy-activating kinases; PDE5—phosphodiesterase-5; COX-2—cyclooxygenase-2; LC3—microtubule-associated proteins light chain 3; NF-κB—nuclear factor kappa B; cGMP—cyclic guanosine monophosphate.

Figure 7

This diagram illustrates the synergistic signaling pathways activated by the combination of metformin, benzimidazole derivatives, and ASA, leading to enhanced autophagy, reduced cellular senescence, and protection against AD. Metformin activates AMPK which inhibits mTORC1, leading to the activation of the ULK1/ATG13 complex and the initiation of macroautophagy. Simultaneously, metformin triggers the TAK1–IKKα/β pathway, promoting CMA for the targeted degradation of pathogenic proteins, while also activating Nrf2-mediated antioxidant responses to protect mitochondrial function. Benzimidazole derivatives, such as albendazole and FLBZ, enhance lysosomal clustering via the JIP4–TRPML1 pathway, improving autophagosome–lysosome fusion and promoting the clearance of toxic aggregates, while independently suppressing NF-κB activity and reducing SASP factors. ASA exerts its effects by stimulating specialized pro-resolving mediators (particularly AT-RvD1), upregulating LC3B and Beclin-1 to boost autophagic flux, and concurrently inhibiting NF-κB signaling to reduce inflammation and SASP expression. Both benzimidazoles and ASA induce microglial polarization toward the anti-inflammatory M2 phenotype, creating a supportive neuroprotective environment. Together, these pathways converge to decrease cellular senescence and neuroinflammation, restore proteostasis, and promote cognitive resilience, ultimately offering protection against the progression of AD.