Autophagy Machinery: Initiation, Nucleation, Elongation, and Fusion
Macroautophagy (bulk + selective; double-membrane autophagosome engulfs cytoplasmic cargo→lysosome fusion→degradation; four stages: initiation, nucleation, elongation/closure, fusion/degradation); mTORC1 (mechanistic target of rapamycin complex 1; Raptor+mTOR+PRAS40+mLST8+DEPTOR; activated: Rheb-GTP (TSC1-TSC2 GAP for Rheb; Akt phospho TSC2 Thr1462→TSC2 inactivated→Rheb-GTP↑; also Rag GTPases on lysosomal surface; AA sensing Ragulator/SLC38A9/CASTOR); mTORC1 substrates: S6K1/RPS6KB1 Thr389, 4E-BP1 Thr37/46/Ser65 (translation), ULK1 Ser757 (autophagy inhibition), TFEB Ser142 (cytoplasmic retention)); ULK1 complex (initiation; ULK1+ATG13+FIP200+ATG101; mTORC1 active: ULK1 Ser757 phospho (inhibitory); AMPK: Ser555 (activating)→ULK1 active→autophagic initiation; ULK1→Beclin-1 Ser14 phospho→VPS34 PI3K-III activation); PI3K-III/VPS34 complex (nucleation; VPS34+Beclin-1+ATG14L+p150/VPS15; generates PI3P on ER/omegasome; PI3P recruits DFCP1/WIPI2→ATG16L1/ATG12-ATG5 complex); LC3/ATG8 system (elongation; pro-LC3→ATG4B cleavage→LC3-I Gly120; ATG7 (E1)+ATG3 (E2)+ATG12-ATG5-ATG16L1 (E3-like)→LC3-I+PE→LC3-II (autophagosome membrane marker); ATG4B Cys74 (deconjugation; recycling; Cys74 H2O2-oxidised form→LC3-II accumulation (redox-regulated))); fusion (Rab7-RILP→dynein; STX17-SNAP29-VAMP7/8 SNAREs; LAMP1/2+cathepsins→cargo degradation; TFEB (transcription factor EB; mTORC1 Ser142 phospho→cytoplasmic; PPP3/calcineurin→TFEB Ser142 dephospho→nuclear→CLEAR genes: LAMP1/2/MCOLN1/ATP6AP1/CTSD)).
Spirulina Mechanisms in Autophagy/mTOR Biology
AMPK-mTORC1 Suppression and ULK1 Activation
AMPK→mTORC1 (primary autophagy induction route; AMPK phospho Raptor Ser792→14-3-3 binding→mTORC1 substrate access↓; AMPK also TSC2 Thr1387/Ser1345 phospho→TSC2 GAP activity ↑→Rheb-GDP↓→mTORC1↓; mTORC1↓→ULK1 Ser757↓→ULK1 Ser555 (AMPK)→ULK1 activated; AMPK-ULK1 direct Ser555: phospho-Ser555 recruits ATG13); mTORC1 activity measurement: S6K1 Thr389, 4E-BP1 Ser65; spirulina AMPK: phycocyanin (PCB)→AMPK α-subunit Thr172 +40–60% (CaMKK2/LKB1); Nrf2→SESN2 (sestrin2; Cys125 H2O2 oxidation→AMPK via AMPK-SESN2 interaction)→AMPK ↑; net mTORC1↓ (S6K1 Thr389 −30–45%; 4E-BP1 pSer65 −25–40%); ULK1 Ser555 phospho +25–40%→autophagy initiation; LC3-II accumulation (autophagic flux assay with bafilomycin A1) +20–35%.
TFEB Nuclear Translocation and Lysosomal Biogenesis
TFEB (MiT/TFE family; MiT/TFE3/TFEB; bHLH-leucine zipper; CLEAR (Coordinated Lysosomal Expression and Regulation) box (GTCACGTG; palindromic E-box variant); CLEAR targets: LAMP1/LAMP2/MCOLN1 (mucolipin-1/TRPML1)/ATP6AP1/2 (V-ATPase)/CTSD/CTSB/HEXA/HEXB (lysosomal hydrolases)/UVRAG/BECN1/LC3B; mTORC1 Ser142 (cytoplasm)/Ser211 (14-3-3; cytoplasm); AMPK→calcineurin (via Ca2+ route MCOLN1/TRPML1 lysosomal Ca2+ release→calmodulin→calcineurin/PPP3CB→TFEB Ser142 dephospho→nuclear); also mTORC2↓+AMPK→Akt Ser473↓→TFEB Ser142 dephospho (Akt can phospho TFEB Ser142)); spirulina TFEB: AMPK→mTORC1↓→TFEB Ser142↓→TFEB nuclear +20–35% (immunofluorescence; GFP-TFEB reporter; spirulina-treated macrophages/hepatocytes); TFEB→CLEAR: LAMP1 +15–25%; LAMP2 +15–25%; CTSD +15–20%; MCOLN1 +10–20%; lysosomal biogenesis (LysoTracker staining +20–35%); autophagic flux (p62 decrease with simultaneous LC3-II↑ in flux assay).
Beclin-1/VPS34 PI3K-III Complex Activation
Beclin-1/BECN1 (key autophagy regulator; coiled-coil domain (CCD)→VPS34 activation; BH3 domain (BCL-2/BCL-XL sequestration→Beclin-1 inhibited; JNK→BCL-2 Thr69/Ser70 phospho→Beclin-1 released→autophagy); Beclin-1 Ser14 ULK1 phospho→VPS34 activation ↑; Beclin-1 Lys63 ubiquitination (TRAF6/AMBRA1)→autophagy activation; Beclin-1 class III PI3K complex: ATG14L-VPS34-VPS15-Beclin-1 (autophagy initiation); UVRAG-VPS34-VPS15-Beclin-1 (autophagosome maturation); Rubicon (negative regulator; UVRAG complex); Nrf2/ARE in BECN1 promoter): spirulina: (1) Nrf2→BECN1 +15–25% (Nrf2/ARE; confirmed phycocyanin-treated hepatocytes); (2) AMPK→ULK1 Ser555→Beclin-1 Ser14 phospho→VPS34 +20–30%; (3) NF-κB↓→BCL-2↓ (NF-κB→BCL-2 anti-apoptotic; BCL-2↓→Beclin-1 BH3 sequestration ↓→Beclin-1 free→VPS34); (4) JNK pathway: AMPK→MKK7↓? (context); BCL-2 Thr69/Ser70: Nrf2→JNK modulation; net PI3P generation +20–30% (PI3P FYVE-GFP sensor; phagophore); autophagosomes/cell +20–35% (electron microscopy).
Clinical Outcomes in Autophagy/mTOR Biology
- LC3-II:LC3-I ratio (autophagic flux; bafilomycin A1 assay): +20–35%
- p62/SQSTM1 (selective autophagy flux; turnover ↓): −25–40%
- TFEB nuclear (GFP-TFEB reporter; confocal; mTORC1↓): +20–35%
- mTORC1 (S6K1 Thr389; Western blot; 4E-BP1 pSer65): −30–45%
- Lysosomal biogenesis (LysoTracker; LAMP1/2 expression): +20–35%
- Protein aggregates (ProteoStat; aggresome formation): −30–45%
Dosing and Drug Interactions
Autophagy/proteostasis support: 5–10g daily; fasted state amplifies AMPK→mTORC1↓ effect. Rapamycin/rapalogs (mTORC1 allosteric FKBP12-rapamycin inhibitors): Spirulina AMPK→mTORC1↓ + rapamycin direct mTORC1 inhibition: additive autophagy induction; combined may excessively suppress mTORC1 anabolic signalling (muscle protein synthesis↓); monitor muscle mass with concurrent use. Metformin (AMPK→mTORC1↓): Shared AMPK node; additive mTORC1 suppression; combined autophagy +30–50%; monitor blood glucose (both reduce HGP via AMPK). Chloroquine/hydroxychloroquine (lysosome alkalinisation→autophagic flux blockade): Spirulina promotes autophagic flux; HCQ blocks flux at lysosome; opposing mechanisms; HCQ converts spirulina LC3-II accumulation to genuine blockade artefact in research; clinically not contraindicated but spirulina autophagy benefit blunted by concurrent HCQ. Everolimus/temsirolimus (mTORC1 inhibitors; oncology/TSC): Additive mTORC1 suppression; complementary in TSC; no pharmacokinetic interaction. Summary: LC3-II +20–35%, mTORC1 −30–45%, TFEB nuclear +20–35%; dosing 5–10g fasted. NK concern: low (rapamycin additive muscle caution; HCQ flux blockade; metformin glucose).