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Macrophage monocarboxylate transporter 1 promotes peripheral nerve regeneration after injury in mice
Mithilesh Kumar Jha, … , Jeffrey D. Rothstein, Brett M. Morrison
Mithilesh Kumar Jha, … , Jeffrey D. Rothstein, Brett M. Morrison
Published September 7, 2021
Citation Information: J Clin Invest. 2021;131(21):e141964. https://doi.org/10.1172/JCI141964.
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Research Article Metabolism Neuroscience

Macrophage monocarboxylate transporter 1 promotes peripheral nerve regeneration after injury in mice

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Abstract

Peripheral nerves have the capacity for regeneration, but the rate of regeneration is so slow that many nerve injuries lead to incomplete recovery and permanent disability for patients. Macrophages play a critical role in the peripheral nerve response to injury, contributing to both Wallerian degeneration and nerve regeneration, and their function has recently been shown to be dependent on intracellular metabolism. To date, the impact of their intracellular metabolism on peripheral nerve regeneration has not been studied. We examined conditional transgenic mice with selective ablation in macrophages of solute carrier family 16, member 1 (Slc16a1), which encodes monocarboxylate transporter 1 (MCT1), and found that MCT1 contributed to macrophage metabolism, phenotype, and function, specifically in regard to phagocytosis and peripheral nerve regeneration. Adoptive cell transfer of wild-type macrophages ameliorated the impaired nerve regeneration in macrophage-selective MCT1-null mice. We also developed a mouse model that overexpressed MCT1 in macrophages and found that peripheral nerves in these mice regenerated more rapidly than in control mice. Our study provides further evidence that MCT1 has an important biological role in macrophages and that manipulations of macrophage metabolism can enhance recovery from peripheral nerve injuries, for which there are currently no approved medical therapies.

Authors

Mithilesh Kumar Jha, Joseph V. Passero, Atul Rawat, Xanthe Heifetz Ament, Fang Yang, Svetlana Vidensky, Samuel L. Collins, Maureen R. Horton, Ahmet Hoke, Guy A. Rutter, Alban Latremoliere, Jeffrey D. Rothstein, Brett M. Morrison

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Figure 1

Selective ablation of MCT1 in macrophages impairs axon regeneration.

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Selective ablation of MCT1 in macrophages impairs axon regeneration.
(A)...
(A) MCT1fl/fl mice were bred with LysM-Cre mice to generate macrophage-specific MCT1-knockout (LysM-Cre MCT1fl/fl) and littermate control (MCT1fl/fl) mice. (B) Schematic representation of the sciatic nerve crush site and electrode setups for the electrophysiological studies. (C) Motor NCV and (D) CMAP amplitude recovery of crushed nerves (percentage relative to the pre-crush value). n = 13 for MCT1fl/fl mice; n = 11 for LysM-Cre MCT1fl/fl mice. *P < 0.05, **P < 0.01, and ***P < 0.001, by 2-way ANOVA with Bonferroni’s multiple-comparison test (C and D). The vertical lines in C and D represent the overall statistical comparison between the data sets from mice of the 2 genotypes. (E and G) Representative photomicrographs of fluorescently labeled NMJs in gastrocnemius muscles after nerve crush. Muscles were stained with α-bungarotoxin (BTX, red) and antibodies against neurofilaments (SMI312; green) and synaptophysin (blue) to visualize acetylcholine receptors (AChRs) and nerve terminals, respectively. Scale bars: 100 μm. (F and H) Percentage of fully reinnervated (Full inn), partially reinnervated (Partial inn), and denervated (Den) AChR clusters in LysM-Cre MCT1fl/fl mice compared with their littermate MCT1fl/fl controls, (F) 3 and (H) 6 weeks after nerve crush. n = 3–4 per group. *P < 0.05, by 2-way ANOVA with Bonferroni’s multiple-comparison test. (I and N) Photomicrographs (scale bars: 20 μm), (J and O) scatter plot graph displaying the g ratios in relation to the axon diameters of individual myelinated axons, (K and P) g ratios, (L and Q) myelinated axon diameters, and (M and R) myelinated axon counts of sural nerves from LysM-Cre MCT1fl/fl and MCT1fl/fl mice after sciatic nerve crush. Light microscope photomicrographs and subsequent analysis were completed on toluidine blue–stained sections. n = 3–4 per group. *P < 0.05 and **P < 0.01, by unpaired, 2-tailed t test (J–M and O–R). All data indicate the mean ± SEM.

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