Berberine activates lysosomal AMPK through an AXIN1‑dependent, PEN2‑independent route[1], whereas metformin relies on PEN2‑mediated lysosomal AMPK activation. This distinction predicts that berberine uniquely stimulates the AMPK‑TFEB signaling cascade, driving lysosomal biogenesis and autophagic flux. We hypothesize that berberine‑induced lysosomal AMPK phosphorylates TFEB, promoting its nuclear translocation and transcriptional upregulation of autophagy genes (e.g., LC3, p62). Enhanced autophagic activity then accelerates the degradation of PCSK9 mRNA and protein through lysosome‑mediated RNA decay, independent of the HNF1α ubiquitination pathway described previously[4](5). Metformin, acting via cytosolic AMPK, does not robustly engage TFEB‑driven autophagy, explaining why its PCSK9‑lowering effect is modest. When combined, berberine supplies the lysosomal autophagy boost while metformin sustains systemic AMPK activation and complex I inhibition[2], resulting in additive or supra‑additive PCSK9 suppression and LDL‑C reduction.

Testable predictions:

1. In primary mouse hepatocytes, berberine (10 µM) will increase phospho‑AMPK (Thr172) on lysosomal fractions (LAMP1+) and increase nuclear TFEB levels within 2 h; metformin will not.
2. Berberine treatment will elevate LC3‑II and decrease p62 in a lysosomal‑dependent manner (blocked by Bafilomycin A1 or lysosomal AMPK knockdown via siAXIN1).
3. PCSK9 mRNA half‑life will be shortened by berberine (>50% reduction) and this effect will be abolished by autophagy inhibition (3‑MA) or TFEB knockdown, but not by HNF1α overexpression.
4. Co‑treatment with berberine + metformin will produce a greater decrease in secreted PCSK9 and LDL‑C in HepG2 cells than either agent alone, an effect lost when autophagy is pharmacologically inhibited.
5. In diabetic db/db mice, hepatic TFEB knockout will attenuate berberine‑induced PCSK9 suppression and LDL‑C lowering, while metformin monotherapy remains unchanged.

Falsifiability: If berberine fails to increase lysosomal AMPK‑TFEB signaling, or if autophagy inhibition does not rescue PCSK9 levels despite berberine exposure, the hypothesis is refuted. Conversely, confirmation would position lysosomal autophagy as a non‑redundant mechanism through which berberine complements metformin, offering a clear biomarker (nuclear TFEB) for patient stratification and guiding dose‑optimization strategies to overcome berberine’s bioavailability limits.