BACKGROUND: The complement cascade is a critical component of the immune system; its activation has been implicated in ALS. Complement (C3) breakdown products are reported to be deposited on ALS NMJs. However, the therapeutic potential of complement system modulation in ALS using clinically relevant human cell-based models is unknown.
OBJECTIVE: Evaluate the effect of C3 inhibition with pegcetacoplan on neuromuscular junction (NMJ) number and function in a human iPSC-derived ALS NMJ model of neuroinflammation.
METHODS: ALS NMJ systems were established by plating human iPSC-derived motoneurons (TDP-43 [G298S] or healthy wild-type [WT] donors), skeletal myoblasts, Schwann cells, and microglia. NMJ systems were combined with unactivated THP-1 monocytes or activated M1 macrophages in a microfluidic co-culture system at a 1:25 ratio (vs. skeletal myoblasts). To determine the effect of C3 inhibition on NMJs, human complement intact serum (hCS; 0.05%) with or without the C3 inhibitor pegcetacoplan (50 µg/mL or 100 µg/mL) was applied for 3 hours before testing. NMJ fidelity was calculated by assessing the ratio of myotube contractions under indirect stimulation to the number of stimuli at a given frequency. Fatigue index (FI) was generated from the area under the curve when muscle contraction demonstrated complete or partial tetanus at 2 Hz.
RESULTS: In this interim analysis of an ALS TDP-43 NMJ system, hCS treatment reduced NMJ numbers to 17.9% of the no dose (ND) control, and increased NMJ FI by 12.2%. NMJ numbers were 79.4% and 75.6% of the ND control in the 50 µg/mL and 100 µg/mL of pegcetacoplan, respectively. Compared to hCS, FI was 9.7% and 46.6% lower in the50 µg/mL and 100 µg/mL of pegcetacoplan, respectively.
CONCLUSIONS: In this interim analysis, inhibiting C3 in an inflammatory environment may improve NMJ survival and function in clinically relevant ALS models.