Dynamic association of APLNR with astrocytic remodeling in the cuprizone-treated corpus callosum

Cuprizone-induced demyelination provides a valuable experimental model for investigating glial responses and endogenous myelin repair in the central nervous system. This study examined the regional behavior of GFAP- and CD44-positive glial populations and their spatial relationship with the apelin receptor (APLNR) in the corpus callosum (CC) of 8-week-old male C57BL/6 mice. Animals were assigned to control, demyelination, and remyelination groups ( n = 10/group). Demyelination was induced by administration of 0.2% cuprizone in drinking water for 5 weeks, followed by a 5-week recovery period. Immunohistochemistry, immunofluorescence, and confocal microscopy were used to assess GFAP, CD44, APLNR, myelin basic protein (MBP), and GST-π-positive mature oligodendrocytes in the lateral (CC-L) and medial (CC-M) CC. Cuprizone induced marked myelin loss and depletion of GST-π-positive oligodendrocytes, followed by partial recovery after withdrawal. Consistent with the established vulnerability of the rostral CC, MBP loss was greater in CC-L than in CC-M. GFAP-positive astrocytic reactivity increased markedly during demyelination and remained more persistent in CC-L during recovery, whereas CD44 showed a distinct phase-dependent regional distribution. APLNR immunoreactivity was minimal under control conditions, increased markedly during demyelination, and remained elevated during remyelination. Its spatial overlap with both GFAP and CD44 was greatest during active demyelination, particularly in CC-L, while correlation analyses further demonstrated region- and phase-dependent relationships between APLNR and astrocytic markers. These findings demonstrate a spatially heterogeneous glial response to cuprizone-induced demyelination and identify a temporally and regionally organized association between APLNR expression and reactive astrocytic populations. The functional significance of this association remains to be established.