Hypothesis

Both thymosin β4 (TB-4) and BPC-157 enhance autophagic flux not by activating the canonical ULK1‑Beclin‑1 pathway, but by stabilizing HIF‑1α under normoxic conditions, which in turn transcriptionally upregulates DAPK1 and Rubicon to drive LC3‑associated phagocytosis (LAP). This positions autophagy as a stress‑gated rationing checkpoint that decides which cytoplasmic constituents are sacrificed for survival, rather than a constitutive housekeeping program.

Mechanistic Rationale

• HIF‑1α stabilization: TB-4 has been shown to inhibit prolyl hydroxylase domain (PHD) proteins in macrophages exposed to Aspergillus conidia, preventing HIF‑1α degradation (see [1]). BPC-157, though mechanistically opaque, contains a hydrophobic pentapeptide motif that can bind Fe²⁺ and competitively inhibit PHD activity, a property shared with known HIF stabilizers such as dimethyloxalylglycine.
• Transcriptional boost: Elevated HIF‑1α drives HIF‑responsive elements (HRE) in the promoters of DAPK1 and Rubicon (RUBCN), increasing their mRNA and protein levels specifically during inflammatory or infectious stress.
• Non‑canonical LAP execution: DAPK1 phosphorylates the phagocytic NADPH oxidase complex (NOX2), facilitating Rubicon‑dependent recruitment of the PI3K‑C3 complex (VPS34‑Beclin‑1‑ATG14L) to nascent phagosomes, thereby lipidating LC3 onto the phagosomal membrane without requiring ULK1 activation.
• Rationing outcome: The LAP‑derived autophagosome preferentially engulfs oxidatively damaged proteins, lipid droplets, or intracellular pathogens, providing amino acids and fatty acids that sustain ATP production while limiting excessive self‑digestion—a true siege‑rationing decision.

Testable Predictions

1. HIF‑1α dependence: In murine bone‑marrow‑derived macrophages (BMDMs), pharmacological inhibition of HIF‑1α (using PX-478) or siRNA‑mediated knock‑down will abolish TB-4‑ and BPC-157‑induced LC3‑II accumulation and the associated increase in DAPK1/Rubicon protein levels following A. fumigatus conidia challenge.
2. Rubicon requirement: CRISPR‑Cas9 knockout of Rubicon in BMDMs will prevent TB-4/BPC-157‑mediated LAP (measured by LC3‑II colocalization with phagosomal marker LAMP1) and will eliminate their protective effects on fungal clearance and cytokine storm attenuation.
3. ULK1 independence: Pharmacological inhibition of ULK1 (MRT68921) or genetic deletion of ULK1 will not diminish TB-4/BPC-157‑driven LC3‑II lipidation under infection, confirming that the observed autophagy is ULK1‑independent.
4. Specificity to stress: Under basal conditions (no conidia, no cytokine stimulus), TB-4 and BPC-157 will fail to increase HIF‑1α, DAPK1, Rubicon, or LC3‑II, reinforcing the stress‑gated nature of the rationing checkpoint.

Experimental Outline

• Cell model: Primary murine BMDMs and human THP‑1 derived macrophages.
• Treatments: TB-4 (1‑10 µM), BPC-157 (1‑10 µM), vehicle, plus A. fumigatus conidia (MOI 5) ± hypoxia mimetic (CoCl₂) as positive control.
• Readouts: Western blot for LC3‑I/II, HIF‑1α, DAPK1, Rubicon; immunofluorescence for LC3‑phagosome colocalization; CFU assay for fungal survival; ELISA for TNF‑α, IL‑6.
• Interventions: PX-478 (HIF‑1α inhibitor), Rubicon sgRNA, ULK1 siRNA, mTOR inhibitor (rapamycin) to confirm pathway specificity.

Falsifiability

If TB-4 and BPC-157 still elevate LC3‑II and reduce inflammation in Rubicon‑deficient macrophages, or if their effects are blocked by ULK1 inhibition but not by HIF‑1α suppression, the hypothesis would be refuted. Conversely, confirmation of the four predictions above would strongly support the view that autophagy, as triggered by these peptides, functions as a stress‑dependent rationing system rather than a generic maintenance pathway.