White matter alterations in Alzheimer's disease without concomitant pathologies

Most individuals with AD neuropathological changes have co-morbidities which have an impact on the integrity of the WM. This study analyses oligodendrocyte and myelin markers in the frontal WM in a series of AD cases without clinical or pathological co-morbidities.

From a consecutive autopsy series, 206 cases had neuropathological changes of AD; among them, only 33 were AD without co-morbidities. WM alterations were first evaluated in coronal sections of the frontal lobe in every case. Then, RT-qPCR and immunohistochemistry were carried out in the frontal WM of AD cases without co-morbidities to analyse the expression of selected oligodendrocyte and myelin markers.

WM demyelination was more marked in AD with co-morbidities when compared with AD cases without co-morbidities. Regarding the later, mRNA expression levels of MBP, PLP1, CNP, MAG, MAL, MOG and MOBP were preserved at stages I-II/0-A when compared with middle-aged (MA) individuals, but significantly decreased at stages III-IV/0-C. This was accompanied by reduced expression of NG2 and PDGFRA mRNA, reduced numbers of NG2-, Olig2- and HDAC2-immunoreactive cells and reduced glucose transporter immunoreactivity. Partial recovery of some of these markers occurred at stages V-VI/B-C.

The present observations demonstrate that co-morbidities have an impact on WM integrity in the elderly and in AD, and that early alterations in oligodendrocytes and transcription of genes linked to myelin proteins in WM occur in AD cases without co-morbidities. These are followed by partial recovery attempts at advanced stages. These observations suggest that oligodendrocytopathy is part of AD.