Gut Senescence-Derived sPtk7 Drives Neuroinflammation via YAP/TEAD-Mediated Microglial Activation

Core Hypothesis

Senescent intestinal epithelial cells release the metalloprotease-shed factor sPtk7 into the bloodstream; sPtk7 crosses the blood-brain barrier through LRP1-dependent transport, binds microglial integrin αvβ3, and triggers YAP/TEAD nuclear translocation. This signaling cascade amplifies NF-κB activity, drives a senescent-like microglial phenotype, and fuels neuroinflammation that accelerates brain aging. Consequently, clearing gut senescence or blocking sPtk7 signaling should attenuate age‑related neuroinflammatory phenotypes even when brain‑intrinsic senescence is unchanged.

Mechanistic Reasoning Beyond Current Data

1. Circulating sPtk7 as a gut‑to‑brain messenger – Intestinal senescence elevates sPtk7 secretion (ref[1]). The protein is small enough (~30 kDa) to diffuse, yet recent work shows LRP1 mediates uptake of analogous SASP factors across the BBB (ref[4] hints at paracrine NADase spread). We propose LRP1 as the primary endothelial receptor for sPtk7, enabling its entry into the CNS parenchyma.
2. Integrin αvβ3 as the microglial sensor – Microglia express high levels of integrin αvβ3, which recognizes RGD motifs present in sPtk7 (predicted from its structure). Binding activates focal adhesion kinase (FAK) and Src, leading to phosphorylation of YAP and its nuclear accumulation, a pathway already linked to intestinal YAP/TEAD dysregulation by sPtk7 (ref[1]).
3. YAP/TEAD amplifies NF‑κB – Nuclear YAP/TEAD complexes cooperate with p65 to enhance transcription of pro‑inflammatory cytokines (IL‑1β, IL‑6, TNF‑α) and CD38, thereby increasing NADase activity and creating a local NAD⁺ depletion loop that sustains microglial senescence (ref[4]).
4. Feed‑forward loop – Activated microglia release additional SASP factors that can increase gut permeability, fostering more intestinal senescence and completing a vicious cycle.

Testable Predictions

• Prediction 1: Aged mice exhibit elevated plasma sPtk7 levels that correlate with cortical YAP/TEAD nuclear localization in microglia and heightened IL‑1β expression.
• Prediction 2: Genetic or pharmacological removal of senescent gut epithelial cells (e.g., villin‑CRE‑ERT2; p16‑3MR model + ganciclovir) reduces plasma sPtk7, diminishes microglial YAP/TEAD activation, and improves performance in hippocampal‑dependent memory tasks without altering brain p16^Ink4a^ burden.
• Prediction 3: Intracerebroventricular infusion of recombinant sPtk7 in young mice induces microglial YAP/TEAD nuclear translocation, increases CD38 expression, and impairs long‑term potentiation; co‑administration of an LRP1 antagonist (RAP) or integrin αvβ3 blocking antibody prevents these effects.
• Prediction 4: Administration of a gut‑restricted senolytic (dasatinib+quercetin encapsulated in pH‑sensitive nanoparticles that release only in the intestinal lumen) lowers plasma sPtk7 and rescues neuroinflammatory markers, whereas the same dose given systemically does not provide additional benefit, confirming the gut‑origin of the signal.

Experimental Approach

1. Plasma profiling – Collect blood from young (3 mo) and aged (24 mo) mice; quantify sPtk7 by ELISA; correlate with immunofluorescence for nuclear YAP/TEAD in Iba1⁺ cells.
2. Gut‑specific senescence ablation – Use villin‑CRE‑ERT2; p16‑3MR mice; administer tamoxifen to induce CRE, then ganciclovir to clear p16^Ink4a^+ gut cells; verify loss of gut p16^Ink4a^ and sPtk7 reduction; assess microglial YAP/TEAD and behavior.
3. BBB transport studies – Inject fluorescently labelled sPtk7 intraperitoneally in wild‑type and Lrp1‑heterozygous mice; measure brain accumulation via confocal imaging; compete with excess RAP.
4. Microglial signaling blockade – Treat mice with integrin αvβ3 antibody (LM609) or YAP inhibitor verteporfin; evaluate cytokine output and cognitive performance after sPtk7 challenge.
5. Senolytic delivery – Formulate dasatinib+quercetin in Eudragit L100‑coated nanoparticles; oral gavage; confirm intestinal release by measuring drug levels in feces vs plasma; assess downstream effects.

Potential Pitfalls and Alternatives

• sPtk7 may be rapidly cleared; need to stabilize with PEGylation for pharmacokinetic studies.
• Integrin αvβ3 is also expressed on endothelial cells; conditional microglia‑specific knockout (Cx3cr1‑CRE‑ERT2; Itgb3^fl/fl^) will isolate microglial contribution.
• Compensatory SASP factors could mask effects; multiplex proteomics will identify secondary mediators.

If these experiments confirm that gut‑derived sPtk7 drives microglial YAP/TEAD activation and neuroinflammation, the longevity intervention stack must prioritize intestinal senescence clearance and BBB‑targeted sPtk7 neutralization before considering brain‑centric senolytics, effectively flipping the gut‑brain axis from a top‑down to a bottom‑up therapeutic axis.