# Targeting the Spinal Cord‐Brain Axis: Electroacupuncture Mitigates Remote Frontal Cortex Neuroinflammation via HMGB1/TLR4 to Aid Functional Recovery After Spinal Cord Injury

## TL;DR

Electroacupuncture helps recover motor function after spinal cord injury by reducing brain inflammation through a specific signaling pathway.

## Contribution

This study shows electroacupuncture's therapeutic effects are causally linked to suppressing the HMGB1/TLR4/NF-κB pathway in the frontal cortex after SCI.

## Key findings

- EA significantly improved locomotor and postural recovery in SCI rats.
- EA suppressed HMGB1/TLR4/NF-κB activation and microglial activation in the frontal cortex.
- Combining EA with HMGB1 inhibition enhanced therapeutic outcomes, validating the pathway as essential.

## Abstract

Beyond the primary lesion, spinal cord injury (SCI) induces secondary neuroinflammation in the frontal cortex, a critical factor exacerbating neural damage and impeding functional recovery. This remote inflammatory response is predominantly regulated by the HMGB1/TLR4 signaling pathway. While electroacupuncture (EA) shows therapeutic promise, whether its efficacy is causally dependent on modulating this supraspinal inflammation remains unproven. This study investigated whether EA promotes functional recovery by suppressing the HMGB1/TLR4/NF‐κB pathway in the frontal cortex of rats with SCI.

One hundred and fifty adult male rats were randomly assigned to Sham, SCI, EA, SCI+ HMGB1 Inhibitor (I), and SCI + EA + HMGB1 Inhibitor (EA + I) groups. Functional recovery was assessed at 1, 7, 14, and 28 days post‐SCI using Basso, Beattie, and Bresnahan (BBB) scores and the inclined plate test. Frontal cortex tissue was analyzed at 7, 14, and 28 days post‐injury for proteins in the HMGB1/TLR4/NF‐κB pathway, TNF‐α (via Western blot and immunofluorescence), and microglial activation (Iba‐1 via immunofluorescence). The mRNA levels of these targets were assessed by qPCR at 7 and 28 days. Spinal cord tissue was evaluated for axonal integrity (NF200 via immunofluorescence) and for motor neuron survival (Nissl staining) at 28 days post‐injury.

EA treatment significantly improved locomotor and postural recovery compared to the SCI group. Concurrently, EA suppressed the SCI‐induced upregulation of HMGB1, TLR4, NF‐κB, and TNF‐α in the brain throughout the subacute (Day 7), transition (Day 14), and chronic (Day 28) phases, thereby inhibiting microglial activation. This neuroprotective effect was accompanied by spinal motor neuron survival and axonal integrity. The co‐administration of an HMGB1 inhibitor with EA established the pathway's necessity by showing that the resulting potentiation of therapeutic outcomes positions the HMGB1/TLR4/NF‐κB axis as a central mechanism for EA.

EA effectively ameliorates motor dysfunction following SCI by attenuating neuroinflammation in the frontal cortex. The underlying mechanism is causally linked to the downregulation of the HMGB1/TLR4/NF‐κB signaling axis. The enhanced neuroprotection observed when combining EA with HMGB1 inhibition validates this signaling axis as the primary and essential target for EA's therapeutic effects in SCI management.

Spinal cord injury (SCI) has been shown to trigger remote neuroinflammation in the frontal cortex via the HMGB1/TLR4/NF‐κB pathway, exacerbating neural damage and impairing functional recovery. The present study demonstrates that electroacupuncture (EA) at GV4 (Mingmen) and GV14 (Dazhui) effectively mitigates this pathological cascade. EA treatment significantly suppressed HMGB1/TLR4/NF‐κB activation and TNF‐α expression in the frontal cortex across the acute, subacute, and chronic phases post‐SCI, accompanied by reduced microglial activation (Iba‐1+ cells). Mechanistically, EA promoted the preservation of spinal motor neurons and axonal integrity (NF200+ fibers), which was associated with an enhancement in locomotor function (Basso, Beattie, and Bresnahan (BBB) scores, inclined plate test). The combination of treatment with an HMGB1 inhibitor (glycyrrhizin) and EA resulted in a potentiation of the therapeutic effects of EA, thereby confirming the HMGB1/TLR4 axis as a critical target for EA's neuroprotective actions. These findings underscore the potential of EA as a promising strategy to modulate the spinal cord‐brain inflammatory axis and enhance functional recovery after SCI.