Conditioned medium from painful non-NF2 schwannomatosis tumors increases pain behaviors in mice

The majority of non-NF2 schwannomatosis (non-NF2 SWN) patients experience debilitating pain. Yet, it is not known why only some schwannomas cause pain or whether mutations in SWN-related genes, (SMARCB1 or LZTR1) differentially influence pain signaling pathways. Here, we established cell lines from non-NF2 SWN tumors resected from patients with varying degrees of pain and bearing mutations in different SWN-related genes. Compared with conditioned medium (CM) collected from "nonpainful" SWN tumors, CM from "painful" SWN tumors contained elevated levels of specific inflammatory cytokines (IL-6, IL-8, VEGF), and was able to enhance sensory neuron responsiveness to noxious TRPV1 and TRPA1 agonists in vitro. In in vivo studies, injection of CM from painful non-NF2 SWN into the hind paws of healthy mice evoked both more acute pain behavior and greater enhancement of mechanical stimulus-evoked behavioral responses than did CM from nonpainful non-NF2 SWN. Furthermore, the behavioral effects of painful CM differed as a function of the SWN-related gene mutations identified in the tumors of origin. Painful SMARCB1 mutant CM, for example, sensitized mice to mechanical stimulation at low forces, compared to non-painful tumor CM and control media, but this effect waned over time. In contrast, CM from a painful tumor with no detectable germline mutation in NF2, SMARCB1 or LZTR1 caused the greatest increase in responsiveness to low mechanical forces and this effect lasted for 2 days post-injection. These experiments establish a paradigm for examining the mechanisms by which painful SWN tumors bearing different mutations produce their sensory effects and will thus facilitate better understanding and, potentially, treatment of the pain endured by non-NF2 SWN patients.