Longitudinal Diffusion Tensor Imaging Revealed Nerve Fiber Alterations in Aspm Mutated Microcephaly Model Mice

Autosomal recessive primary microcephaly-5 (MCPH5) is characterized by congenital microcephaly and is caused by the mutation in the abnormal spindle-like, microcephaly-associated (ASPM) gene. This study aimed to demonstrate a correlation between radiological and pathological analyses in evaluating postnatal brain development using MCPH5-model mice, ASPM ortholog (Aspm) knockout (KO) mice. In vivo MRI was performed at two time points (postnatal 3 weeks; P3W and P10W) and complementary histopathological analyses of brains were done at P5W and P13W. In the MRI analysis, Aspm KO mice showed significantly decreased brain sizes (average 8.6% difference) with larger ventricles (average 136.4% difference) at both time points. Voxel-based statistics showed that the fractional anisotropy (FA) values were significantly lower in Aspm KO mice in both the cortex and white matter at both time points. Developmental changes in the FA values were less remarkable in the Aspm KO mice, compared with the controls. Histometric analyses revealed that the ratios of the horizontal to the vertical neurites were significantly higher in cortical layers IV, V and VI, with a remarkable increase according to maturation at P13W in the control mice (average 12.7% difference between control and KO), whereas the ratio in layer VI decreased at P13W in the KO mice. The myelin basic protein positive ratio in the white matter significantly decreased in Aspm KO mice at P5W. These results suggest that temporal FA changes are closely correlated with pathological findings such as abnormal neurite outgrowth and differentiation, which may be applicable for analyzing diseased human brain development.