IGF-1 signaling pathway activation promotes axonal regeneration and repair: A mechanism study on catalpol-induced functional recovery after ischemic stroke.

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese Medicine (TCM) theory, there is a concept of "tonifying the kidney and generating marrow, and marrow enriches and nourishes the brain ", which believes that tonifying the kidney and generating marrow can promote brain marrow repair and neurological function recovery. This theoretical framework has been substantiated by multiple modern medical studies. Catalpol, a bioactive iridoid glycoside extracted from Rehmannia glutinosa (Gaertn.) DC. has been traditionally employed in TCM for "kidney tonification, marrow generation, and brain nourishment". Regenerative remodeling of corticospinal tracts (CST) mediated by axonal regeneration, collateral formation, and neural network reconstruction is critical for neurological recovery after ischemic stroke. As the primary active component of Rehmannia glutinosa, catalpol may manifest the traditional medicinal effects of promoting neurological recovery through modern neuroregenerative mechanisms.

AIM OF THE STUDY

To verify whether catalpol promotes neurological recovery after ischemic stroke and elucidate its underlying mechanisms.

METHODS

Potential therapeutic targets of catalpol were first identified through network pharmacology coupled with cellular thermal shift assay (CETSA) validation. In vivo experiments utilized a photothrombotic (PT) stroke mouse model, in which catalpol's effects on neurological recovery were quantitatively assessed using behavioral tests. Axonal regeneration dynamics and IGF-1 pathway activation were systematically evaluated through functional magnetic resonance imaging (fMRI) for CST remodeling, growth-associated protein 43 (GAP43) and myelin basic protein (MBP) immunofluorescence for axonal sprouting quantification, and Western blotting for insulin-like growth factor-1 (IGF-1), insulin-like growth factor-1 receptor (IGF-1R), mammalian target of rapamycin (mTOR), and GAP43 expression profiling. Complementary in vitro studies employing oxygen-glucose deprived (OGD) neurons demonstrated catalpol's effects on proliferation, migration and axonal growth using Cell Counting Kit-8 (CCK-8), immunofluorescence, scratch wound assay and Western Blot. Mechanistic specificity was confirmed through pharmacological IGF-1R inhibition with linsitinib.

RESULTS

Catalpol was found to directly bind to IGF-1R, as evidenced by molecular docking (binding energy: -6.5 kcal/mol) and CETSA (ΔTm = 4.38 °C). In vivo, catalpol treatment significantly improved motor and sensory recovery in post-stroke mice, reducing error rates in irregular ladder walking (P = 0.014 vs. model) and shortening sticker removal times (P = 0.0043 vs. model), effects that were abolished by IGF-1R inhibition with linsitinib. Diffusion tensor imaging revealed enhanced fractional anisotropy (FA) values in corticospinal tract regions (e.g., dorsal fornix: P = 0.0496), alongside increased axonal markers GAP43 and MBP expression (P < 0.01) in peri-infarct tissues. In vitro, catalpol rescued oxygen-glucose deprivation (OGD)-induced neuronal damage, promoting SH-SY5Y cell viability (P < 0.01), neurite elongation (P < 0.0001), and scratch wound closure (P < 0.001). Mechanistically, catalpol upregulated IGF-1R phosphorylation, activated mTOR signaling, and suppressed phosphatase and tensin homolog deleted on chromosome ten (PTEN), thereby elevating GAP43, osteopontin (OPN), and p-S6 levels (P < 0.05-0.001). Co-treatment with linsitinib negated these effects, confirming the dependency on IGF-1R/mTOR/PTEN axis. These findings establish catalpol as a multimodal neuroregenerative agent targeting IGF-1 signaling to drive axonal repair and functional recovery post-stroke.

CONCLUSION

Our research elucidates that catalpol improves neurological recovery in ischemic stroke by regulating the IGF-1 signaling pathway to promote axonal regenerative repair, providing a new perspective for addressing the challenge of functional recovery in ischemic stroke.