Dp71 contribution to the molecular scaffold anchoring aquaporine‐4 channels in brain macroglial cells

Abstract

Intellectual disability in Duchenne muscular dystrophy has been associated with the loss of dystrophin‐protein 71, Dp71, the main dystrophin‐gene product in the adult brain. Dp71 shows major expression in perivascular macroglial endfeet, suggesting that dysfunctional glial mechanisms contribute to cognitive impairments. In the present study, we investigated the molecular alterations induced by a selective loss of Dp71 in mice, using semi‐quantitative immunogold analyses in electron microscopy and immunofluorescence confocal analyses in brain sections and purified gliovascular units. In macroglial pericapillary endfeet of the cerebellum and hippocampus, we found a drastic reduction (70%) of the polarized distribution of aquaporin‐4 (AQP4) channels, a 50% reduction of β‐dystroglycan, and a complete loss of α1‐syntrophin. Interestingly, in the hippocampus and cortex, these effects were not homogeneous: AQP4 and AQP4ex isoforms were mostly lost around capillaries but preserved in large vessels corresponding to pial arteries, penetrating cortical arterioles, and arterioles of the hippocampal fissure, indicating the presence of Dp71‐independent pools of AQP4 in these vascular structures. In conclusion, the depletion of Dp71 strongly alters the distribution of AQP4 selectively in macroglial perivascular endfeet surrounding capillaries. This effect likely affects water homeostasis and blood–brain barrier functions and may thus contribute to the synaptic and cognitive defects associated with Dp71 deficiency.

Emotional behavior and brain anatomy of the mdx52 mouse model of Duchenne muscular dystrophy

“…We also confirmed the preserved expression of Dp71, typically detected along the walls of blood vessels in both wild-type and mdx52 mice ( ), due to its main expression at the membrane of perivascular astrocyte endfeet forming the blood-brain barrier ( Belmaati Cherkaoui et al, 2020 ).…”

“…Dp140 is more highly expressed in the human fetal brain than in the adult brain ( Doorenweerd et al, 2017 ; Lidov et al, 1995 ; Morris et al, 1995 ), which suggests it is involved in brain formation, perhaps in neuronal proliferation or migration ( Hildyard et al, 2020 ; Romo-Yáñez et al, 2020 ). Moreover, the loss of distinct dystrophins reduces the expression of the membrane-spanning core protein of the dystrophin-associated complex, dystroglycan ( Kameya et al, 1997 ; Culligan et al, 2001 ; Daoud et al, 2009b ; Benabdesselam et al, 2012 ; Belmaati Cherkaoui et al, 2020 ). Dystroglycan has been implicated in basement membrane formation, cell migration and corticogenesis ( Paprocka et al, 2021 ), as defective glycosylation of the extracellular component of the dystroglycan subcomplex results in defects of the glia limitans and cortical plate disorganization, with overmigration of neurons into the arachnoid space in the Walker–Warburg, Fukuyama congenital muscular dystrophy and muscle-eye-brain syndromes associated with intellectual disability ( Godfrey et al, 2007 ; Guimaraes and Dahmoush, 2020 ).…”

“…This suggests that the neural dysfunctions resulting from the cumulative loss of these two dystrophins rather take place at the level of brain cellular functionalities. Dp427 has been implicated in GABAergic inhibition and blood-brain barrier functions due to its expression in central inhibitory synapses and vascular smooth muscles, respectively ( Belmaati Cherkaoui et al, 2020 ; Fritschy et al, 2012 ; Nico et al, 2003 ). In contrast, the localization and function of Dp140 remain largely unknown.…”

“…The loss of brain Dp427 appears to particularly alter the functionality of the neuronal network involved in the processing of fear responses, as demonstrated in mdx mice by the presence of drastically enhanced fearfulness in response to mild stress and delayed fear learning and memory ( Goyenvalle et al, 2015 ; Razzoli et al, 2020 ; Sekiguchi et al, 2009 ; Vaillend and Chaussenot, 2017 ). In contrast, the selective loss of Dp71 in mice does not induce muscular dystrophy ( Sarig et al, 1999 ) but alters critical molecular mechanisms involved in excitatory synapse and astrocyte functions ( Belmaati Cherkaoui et al, 2020 ; Daoud et al, 2009b ), which results in a different profile of behavioral disturbances, including deficits in spatial learning, working memory and cognitive flexibility ( Chaussenot et al, 2019 ; Helleringer et al, 2018 ). However, so far, there has been very limited behavioral studies of mouse models with distal mutations leading to cumulative loss of several dystrophins ( Vaillend et al, 1998 ; Vaillend and Ungerer, 1999 ).…”

Emerging roles for dynamic aquaporin-4 subcellular relocalization in CNS water homeostasis

“…Deletion of the Dmd and Snta1 genes (which encode the DAC proteins, dystrophin and αsyntrophin), or of Agrn (which encodes the basal lamina protein, agrin) in mice results in the loss of this perivascular AQP4 localization. [24][25][26][27] A recent study also suggests a potential role for β-syntrophin in AQP4 anchoring. 28 Changes in perivascular localization of AQP4 have been reported across myriad pathological conditions, including CNS tumours, neurovascular disorders such as ischaemic stroke and traumatic brain injury (TBI), and in the setting of neurodegenerative disease.…”