Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease where muscle weakness and neuromuscular junction (NMJ) denervation precedes motor neuron cell death. Although acetylcholine is the canonical neurotransmitter at the mammalian NMJ synapse, glutamate has recently been identified as a critical neurotransmitter for NMJ development and maintenance. Glutamate can be produced through the catabolism of the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG), which is released upon stimulation, and hydrolyzed to glutamate by the enzyme glutamate carboxypeptidase II (GCPII). 2-PMPA is a potent GCPII inhibitor which robustly blocks glutamate release from NAAG but is highly polar with limited tissue penetration. To improve this, we covalently attached 2-PMPA to a hydroxyl polyamidoamine (PAMAM-G4-OH) dendrimer delivery system (D-2PMPA) which is known to target activated macrophages in affected tissues. In primary murine macrophage cultures, we observed a significant increase in GCPII enzymatic activity following GM-CSF+IL4 stimulation. Using the SOD1G93A model of ALS, we found an almost 4-fold elevation of GCPII enzymatic activity in SOD1G93A versus WT muscle and a robust increase in GCPII protein expression which was specifically associated with activated macrophages infiltrating the muscle. Systemic D-2PMPA therapy (20 mg/kg IP 2x/week) was found to selectively localize in muscle macrophages in SOD1G93A mice and completely normalize the enhanced GCPII activity. Although no changes in body weight or survival were observed, D-2PMPA significantly improved grip strength and inhibited the loss of NMJ innervation in the gastrocnemius muscles. Our findings demonstrate that elevated macrophage-associated GCPII activity may have negative effects on neuromuscular integrity in ALS and that inhibiting this elevated GCPII activity in SOD1G93A muscle can prolong muscle function and delay NMJ denervation, which may have early therapeutic implications for ALS patients.