Sex-dependent effects of the targeted nerve growth factor mutation (R100E) on pain behavior, joint inflammation, and bone erosion in mice.

Nerve growth factor (NGF)-R100E is a mutated form of human recombinant NGF that reduces the binding of NGF to its p75NTR receptor while retaining its affinity toward the TrkA receptor. Here, we used human wild type NGF and NGF-R100E knock-in mice to investigate the effects of this NGF mutation on inflammation-induced pain-related behaviors and bone loss. The hNGF-R100E mutation did not alter the nerve fiber density in the sciatic nerve, ankle joint synovium, and skin of naïve mice. Withdrawal responses to mechanical, thermal, and cold stimuli before and after joint inflammation induced by intra-articular injection of complete Freund adjuvant (CFA) were similar between human recombinant nerve growth factor-wild type and hNGF-R100E male and female mice while weight bearing and gait analysis revealed significant differences. Intriguingly, hNGF-R100E male and female mice showed only mild changes, indicating lower degrees of deep joint-related pain compared to their wild type counterparts. Furthermore, micro-CT analysis demonstrated that hNGF-R100E female mice, but not males, were protected from CFA-induced bone loss, and mRNA analysis showed a different gene regulation indicating a sex-dependent relationship between NGF, inflammation, and bone loss. In conclusion, our study reveals that the hNGF-R100E mutation renders mice insensitive to inflammation-induced impact on joint loading and gait while preserving the development of the peripheral nociceptive neurons and sensitivity to punctate stimulation of the skin. Notably, the mutation uncovers a sex-dependent relationship between NGF and inflammation-induced bone loss. These findings offer valuable insights into NGF as a target for pain management and the interplay between NGF and bone architecture.