NMJ Retrograde Signaling
EXPLORATORYPhase 7.3 — Muscle-to-nerve retrograde signaling at the neuromuscular junction. Tests the “happy muscle → surviving neuron” hypothesis: can improving muscle health rescue motor neurons via retrograde trophic signals?
Retrograde Signals
| Signal | Type | Source → Target | SMA Status | Potential | Strategy |
|---|---|---|---|---|---|
| BDNF (muscle-derived) | protein | muscle fiber → motor neuron soma | reduced | 80% | Muscle-specific BDNF overexpression or engineered EV delivery of BDNF to NMJ. |
| Agrin | protein | motor neuron terminal → muscle fiber (NMJ) | reduced | 75% | Agrin mimetic (Z+ agrin fragment) injection or AAV-agrin to rescue NMJ integrity. |
| GDNF | protein | muscle fiber → motor neuron soma | reduced | 75% | GDNF gene therapy to muscle; sustained local delivery to NMJ. |
| Muscle-derived EVs (exosomes) | exosome | muscle fiber → motor neuron soma | reduced | 70% | Engineered EVs loaded with miR-206 + BDNF + agrin for NMJ-targeted delivery. |
| NT-4/5 | protein | muscle fiber → motor neuron soma | reduced | 65% | Recombinant NT-4/5 supplementation targeted at fast-fatigable MN subtypes. |
| Gdf5/BMP (Glass bottom boat) | protein | muscle fiber → presynaptic terminal | reduced | 60% | Recombinant Gdf5 supplementation or BMP pathway activation in muscle. |
| Schwann cell-derived VEGF | protein | terminal Schwann cell → motor neuron terminal | reduced | 55% | VEGF-A supplementation or Schwann cell activation to restore glial NMJ support. |
| Laminin-beta2 (LAMB2) | protein | muscle fiber → presynaptic terminal | reduced | 50% | LAMB2 supplementation or AAV-mediated restoration in muscle basement membrane. |
| FGF-BP1 | protein | muscle fiber → presynaptic terminal | reduced | 50% | FGF-BP1 recombinant protein delivery or expression modulation at NMJ. |
| Endocannabinoids (2-AG) | lipid | muscle fiber → presynaptic terminal | normal | 40% | Not a primary target; modulation could tune synaptic homeostasis in advanced disease. |
EV Therapeutic Cargo
| Cargo | Type | Function | SMA Context | Feasibility |
|---|---|---|---|---|
| miR-206 | mirna | NMJ maturation signal; promotes AChR clustering and NMJ integrity. | Downregulated in SMA muscle; restoring it delays denervation. | 75% |
| BDNF protein | protein | Neuroprotective survival signaling via TrkB. | Reduced at SMA NMJ; low endogenous muscle production. | 70% |
| miR-1 | mirna | Muscle differentiation and ion channel regulation. | Reduced in SMA; affects muscle fiber identity. | 70% |
| miR-133a | mirna | Muscle proliferation/differentiation balance. | Altered in SMA; disrupts satellite cell homeostasis. | 65% |
| Agrin fragment | protein | AChR clustering and NMJ stability via MuSK/LRP4. | Reduced agrin in SMA leads to NMJ fragmentation. | 65% |
| HSP70 | protein | Chaperone; protein quality control; anti-apoptotic in MNs. | Reduced MN protection in SMA; HSP70 overexpression extends survival in mouse models. | 60% |
| SMN mRNA | mrna | Direct SMN protein production in target cells. | Absent (root cause of SMA); mRNA delivery bypasses splicing defect. | 55% |
Organ-on-Chip Models
High-throughput NMJ plate (optogenetic)
TRL 6 · $20-40
Optogenetic activation isolates muscle vs neural defects; SMA compounds testable at scale.
Cells: iPSC-MNs (ChR2), Engineered muscle strips, 96-well format
Readouts: Light-evoked contraction, Force measurement, Compound screening
Supplier: Acuitas / AxoSim / custom
NMJ-on-Chip (2-compartment)
TRL 5 · $50-100
SMA patient iPSC-derived MNs show reduced NMJ formation and contraction force.
Cells: iPSC-MNs, C2C12 myotubes, Matrigel channel
Readouts: Contraction force, AChR clustering, Calcium imaging, Electrophysiology
Supplier: Hesperos / custom academic fab
Motor Unit-on-Chip (3-compartment)
TRL 4 · $100-200
Models complete motor unit with glial support — captures Schwann cell defects in SMA.
Cells: iPSC-MNs, Primary myofibers, Schwann cells, Microfluidic gradient
Readouts: Axon growth, Myelination, NMJ maturation, Retrograde transport
Supplier: Custom academic / Mimetas