Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation
Bermans J. Iskandar, … , Thomas D. Cook, Kirk J. Hogan
Bermans J. Iskandar, … , Thomas D. Cook, Kirk J. Hogan
Published April 26, 2010
Citation Information: J Clin Invest. 2010;120(5):1603-1616. https://doi.org/10.1172/JCI40000.
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Research Article

Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation

Abstract

The folate pathway plays a crucial role in the regeneration and repair of the adult CNS after injury. Here, we have shown in rodents that such repair occurs at least in part through DNA methylation. In animals with combined spinal cord and sciatic nerve injury, folate-mediated CNS axon regeneration was found to depend on injury-related induction of the high-affinity folate receptor 1 (Folr1). The activity of folate was dependent on its activation by the enzyme dihydrofolate reductase (Dhfr) and a functional methylation cycle. The effect of folate on the regeneration of afferent spinal neurons was biphasic and dose dependent and correlated closely over its dose range with global and gene-specific DNA methylation and with expression of both the folate receptor Folr1 and the de novo DNA methyltransferases. These data implicate an epigenetic mechanism in CNS repair. Folic acid and possibly other nontoxic dietary methyl donors may therefore be useful in clinical interventions to promote brain and spinal cord healing. If indeed the benefit of folate is mediated by epigenetic mechanisms that promote endogenous axonal regeneration, this provides possible avenues for new pharmacologic approaches to treating CNS injuries.

Authors

Bermans J. Iskandar, Elias Rizk, Brenton Meier, Nithya Hariharan, Teodoro Bottiglieri, Richard H. Finnell, David F. Jarrard, Ruma V. Banerjee, J.H. Pate Skene, Aaron Nelson, Nirav Patel, Carmen Gherasim, Kathleen Simon, Thomas D. Cook, Kirk J. Hogan

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Figure 6

Combined spinal cord and peripheral nerve injury inhibits methyl cycling, SAM bioavailability, and MS activity; and MS inhibition abolishes folate-mediated axonal regeneration.

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Combined spinal cord and peripheral nerve injury inhibits methyl cycling...
Injury to the rat spinal cord and left sciatic nerve causes a diminution in the SAM/SAH ratio (n = 6 [normal]; n = 6 [injured]. Student’s t test; mean ± SEM; *P < 0.05) (A), suggesting a direct effect of injury on DNA methylation. To confirm this observation, spinal axonal regeneration was measured in the SCRM model on the “conditioned” side after treatment with N2O. N2O is a specific inhibitor of the MS enzyme; thus it interferes with the entry of active folate into the methionine methylation cycle. N2O suppressed axon growth to below control levels. n = 10 (untreated); n = 7 (FA); n = 8 (N2O); n = 8 (FA). One-way ANOVA with Bonferroni’s correction; mean ± SEM; *P < 0.05 (B). To determine whether N2O suppresses MS, MS activity and SAH levels were measured in the spinal cord after N2O exposure. N2O suppressed MS activity (C) with no change in the enzyme protein levels by Western analysis (not shown) and caused a corresponding rise in SAH (D). Note the drop in MS activity after injury and after N2O treatment. Recovery from the N2O effect occurs by 3 days (C). N, no injury; S, spinal cord injury; N0 and S0, No N2O treatment; N1, N2O given the day before removing the spinal tissue; N2, N2O given 3 days before removing the spinal tissue; S1, N2O treatment every other day for 2 weeks; S2, N2O given 2 weeks before removing spinal tissue. n = 3 in each group; each specimen was run in triplicate. One-way ANOVA with Bonferroni’s correction; mean ± SEM, *P < 0.05.