A1 adenosine receptors mediate hypoxia-induced ventriculomegaly

Abstract

Periventricular leukomalacia is characterized by a reduction in brain matter and secondary ventriculomegaly and is a major cause of developmental delay and cerebral palsy in prematurely born infants. Currently, our understanding of the pathogenesis of this condition is limited. In animal models, features of periventricular leukomalacia can be induced by hypoxia and activation of A1 adenosine receptors (A1ARs). Using mice that are deficient in the A1AR gene (A1AR-/-), we show that A1ARs play a prominent role in the development of hypoxia-induced ventriculomegaly in neonates. Supporting a role for adenosine in the pathogenesis of developmental brain injury, ventriculomegaly was also observed in mice lacking the enzyme adenosine deaminase, which degrades adenosine. Thus, adenosine acting on A1ARs appears to mediate hypoxia-induced brain injury ventriculomegaly during early postnatal development.

Fig. 1.

Hematoxylin-stained coronal sections from +/+, +/–, or –/– A₁AR animals taken from the midstriatum of P14 mice exposed from P3 through P14 to either chronic sublethal hypoxia (9.5% O₂) or room air. Ventricular enlargement was observed in +/+ and +/– mice exposed to hypoxia but not in –/– mice exposed to hypoxia and +/+ mice reared in normoxia. (Scale bar: 1 mm.)

Fig. 2.

Ventricular area as related to genotype and oxygen exposure. Numbers representing animals in each group are indicated along the x axis. Means ± SEM are presented. **, P < 0.01 vs. +/+ or +/– in room air and –/– in 9.5% O₂. ##, P < 0.01 vs. +/– in 9.5% O₂.

Fig. 3.

MBP immunoreactivity in coronal sections of the corpus callosum from +/+, +/–, or –/– A₁AR at midstriatum level of P14 mice exposed from P3 through P14 to either chronic sublethal hypoxia (9% O₂) or room air. (Scale bar: 0.2 mm.)

Fig. 4.

Western blot analysis of MBP immunoreactivity in whole brain from +/+ or –/– A₁AR littermates exposed from P3 through P14 to either room air (RA) or chronic sublethal hypoxia (9% O₂). After detection with anti-MBP antibody, the blot was stripped and reprobed with antibodies to GAPDH.

Fig. 5.

(A and B) Hematoxylin-stained coronal sections from Ada+/+ or Ada–/– animals taken from the midstriatum of P17 neonates and stained with hematoxylin. Ventricular enlargement was seen in Ada–/– but not in Ada+/+ mice. (C and D) Adjacent sections to those shown in A and B were stained with a primary antibody to MBP. CC, corpus callosum; SCW, subcortical white matter. (E) Quantitative assessment of ventricular areas at the same level shown in A and B. (Scale bars: B, 1 mm; D, 0.2 mm.)