11beta-Hydroxysteroid dehydrogenase type 2 protects the neonatal cerebellum from deleterious effects of glucocorticoids

Abstract

11beta-Hydroxysteroid dehydrogenase type 2 is a glucocorticoid metabolizing enzyme that catalyzes rapid inactivation of corticosterone and cortisol to inert 11-keto derivatives. As 11beta-hydroxysteroid dehydrogenase type 2 is highly expressed in the developing brain, but not in the adult CNS, we hypothesized that it may represent a protective barrier to the deleterious actions of corticosteroids on proliferating cells. To test this hypothesis we have investigated the development and growth of the cerebellum in neonatal C57BL/6 mice and mice lacking 11beta-hydroxysteroid dehydrogenase type 2 (-/-). 11beta-Hydroxysteroid dehydrogenase type 2-/- mice had consistently lower body weight throughout the neonatal period, coupled with a smaller brain size although this was normalized when corrected for body weight. The cerebellar size was smaller in 11beta-hydroxysteroid dehydrogenase type 2-/- mice, due to decreases in size of both the molecular and internal granule layers. When exogenous corticosterone was administered to the pups between postnatal days 4 and 13, 11beta-hydroxysteroid dehydrogenase type 2(-/-) mice were more sensitive, showing further inhibition of cerebellar growth while the wildtype mice were not affected. Upon withdrawal of exogenous steroid, there was a rebound growth spurt so that at day 21 postnatally, the cerebellar size in 11beta-hydroxysteroid dehydrogenase type 2-/- mice was similar to untreated mice of the same genotype. Furthermore, 11beta-hydroxysteroid dehydrogenase type 2-/- mice had a delay in the attainment of neurodevelopmental landmarks such as negative geotaxis and eye opening. We therefore suggest that 11beta-hydroxysteroid dehydrogenase type 2 acts as to protect the developing nervous system from the deleterious consequences of glucocorticoid overexposure.

Fig. 1. Pattern of 11ß-HSD2 mRNA expression in neonatal cerebellum.

11ß-HSD2 mRNA expression in EGL cerebellum at P7, 10 and 14. No expression is seen in adult cerebellum. The only significant expression of 11ß-HSD2 mRNA in adult mouse brain is in nucleus tractus solitarius.

Fig. 2. Neonatal growth curve of 11ß-HSD2^-/- and C57BL/6 controls.

(a) Body weights, (b) brain weights and (c) brain/body weight ratios of control C57BL/6 mice (solid columns) and 11ß-HSD2^-/- mice (open columns) at 7, 14 and 21 postnatally. Values are means±S.E.M., n= 5–12/group. * P<0.05 compared with respective C57BL/6 value.

Fig. 3. Altered growth of the cerebellum in 11ß-HSD2^-/- compared with controls.

(a) Midsagittal section of mouse cerebellum indicating zonations. Box indicates area used in cell counting (see Table 2). Comparative measurements of mid-sagittal area of (b) total cerebellum, (c) ML and (d) IGL removed from C57BL/6 control (black columns and solid lines with closed symbols) and 11ß-HSD2^-/- (open columns and dotted line with open symbols) mice at P7, 14 and 21. Values are means±S.E.M., n=4– 6/group. * P<0.05 compared with respective C57BL/6 value.

Fig. 4. Immunohistochemistry for GFAP staining of Bergman glia projections in cerebellum from C57BL/6 and 11ß-HSD2^-/- neonates.

Representative midsagittal sections of cerebellum removed from C57BL/6 control or 11ß-HSD2^-/- mice and stained for GFAP expression at P14 and 21. Glia projections appear more fragmented at P21 in C57BL/6 sections compared with 11ß-HSD2.

Fig. 5. Altered cerebellar size following treatment with exogenous corticosterone. Corticosterone was administered to mice from P4-13.

The size of (a) cerebellum, (b) the ML and (c) IGL measured in midsagittal sections was compared in untreated C57BL/6 (black columns) and 11ß-HSD2^-/- (open columns) mice with corticosterone treated C57BL/6 (striped columns) and 11ß-HSD2^-/- (hatched columns) mice. Values are means±S.E.M., n=4– 6/group. * P<0.05 compared with untreated controls of the same genotype.

Fig. 6. Developmental landmarks.

Percentage of C57BL/6 mice (black columns) and 11[-HSD2^-/- mice (open columns) that complete negative geotaxis within one minute at P7 and have both eyes open at P14. Number of animals/group is shown in parentheses.