LAUSR

DMF-mediated anti-inflammatory, anti-oxidative or a synergism of both effects may be sufficient to propagate nerve regeneration in a primary mechanical injury model. To evaluate the efficacy of DMF during Wallerian degeneration, we performed sciatic nerve crush in C57BL/6 mice, which were treated daily with 100 mg/kg DMF over the course of 12 days, starting 2 days before crush injury until 9 days post-crush. Nerve functionality was assessed via grip strength analysis of both the injured and the contralateral non-injured hindlimbs (Fig. 1a). Following a strong impairment of grip strength at 7 days post-crush, 14 days after injury, we observed a similar extent of recovery in vehicle as well as DMF treated mice. However, at 21 days post-crush, recovery of grip strength in DMF-treated mice was significantly improved compared to vehicle treated mice. To confirm our finding for this clinical parameter, we performed nerve conduction tests at 14 and 21 days postcrush (Fig. 1b; supplementary fig. 1), revealing a significant elevation of nerve conduction velocity in DMF-treated mice at the latter stage. To complement these data with histological measures, we investigated the impact of DMF on myelin thickness via g-ratio measurements (the numerical ratio between axonal and whole myelinated fibre diameter) from semi-thin sections (Fig. 1c). Between 14 and 21 days post-crush, we observed a gradual improvement of myelination in DMF-treated mice, whereas myelin thickness remained significantly reduced in control mice (Fig. 1d, e; supplementary fig. 2). To decipher whether DMF treatment would modulate protective pathways during Wallerian degeneration, we investigated the localization of Nrf2 on sciatic nerve sections by immunohistochemistry at 6 days post-crush. We recognized a greater extent in the co-localization of Nrf2 and nuclear staining, and found nuclear Nrf2 immunofluorescence intensity to be significantly increased in response to injury; DMF treatment further enhanced Peripheral nerves exhibit a remarkable ability to regenerate; however, there is an unmet need to better understand relevant pathways that could support or even accelerate this process. Fumaric acid esters, especially its dimethyl ester (DMF), are an established treatment option for autoimmune diseases [7]. DMF is known to activate the NFE2-related factor 2 (Nrf2) transcription factor [8] which is ubiquitously and constitutively expressed and primarily localized in the cytoplasm. Its suppressor, Kelch-like ECHassociated protein 1 (Keap1), prevents Nrf2 from entering the nucleus and acts as an adaptor protein for Nrf2 ubiquitinylation. In case of oxidative or electrophilic stress, Nrf2 is released from Keap1 and translocated into the nucleus to induce antioxidant response element (ARE) gene expression [5]. Additionally, Nrf2 has been demonstrated to induce the expression of heme oxygenase 1 (HO-1) [1], a potent cytoprotective and anti-inflammatory enzyme [9, 10]. An emerging body of experimental evidence suggests that DMF, targeting Keap1 and interfering with the Nrf2/Keap1 interaction, indirectly activates Nrf2 by enabling its translocation into the nucleus [3]. The upregulation of HO-1 expression or activation of anti-oxidative mechanisms has been suggested to account for the efficacy of DMF [2, 4, 6, 8]. To date, it remains unclear whether