CHANGE IN AQUAPORIN-4 EXPRESSION AND LOCALIZATION DURING AMYOTROPHIC LATERAL SCLEROSIS AND SPINAL MUSCULAR ATROPHY PROGRESSION

The glymphatic system is a glial-dependent perivascular network responsible for clearing waste and neurotoxic substances from the central nervous system. Aquaporin-4 (AQP4) water channels, expressed on the astrocyte endfeet and localized around blood vessels, are key components of this system. Dysfunction of the glymphatic pathway has been associated with several neurodegenerative diseases, including Alzheimer’s disease and Amyotrophic Lateral Sclerosis (ALS). Our purpose was to evaluate if the alterations in AQP4 expression may also contribute to neurodegeneration in ALS and Spinal Muscular Atrophy (SMA), two different motor neuron diseases. We investigated AQP4 expression in the ventral horns of spinal cord in delta7SMN and SOD1G93A mice, respectively SMA and ALS models. Three time points were selected to represent the presymptomatic, early symptomatic, and late disease stages. The lumbar spinal cord was collected, sectioned at 40 μm, and processed for immunofluorescence analysis using antibodies against AQP4, GFAP (astroglial marker) and ChAT (motor neuron marker). Images were acquired with a Zeiss Apotome microscope and analyzed with ImageJ. We observed a significant increase in AQP4 expression in SOD1G93A mice at both early and late disease stages compared to healthy controls: specifically, during these stages, AQP4 levels in the peri-motoneuronal region increased by 89.8% and 45.6%, respectively, in ALS mice relative to controls. In addition, an increasing trend in AQP4 expression was detected between the presymptomatic and early disease stages. Conversely, AQP4 levels decreased at the late stage, possibly due to neurodegeneration. Comparable expression patterns were observed in SMA mice, in which the increase between the presymptomatic and early stages reached approximately 36%. Our study highlights a potential contribution of the glymphatic system in the pathogenesis of motor neuron diseases and suggests AQP4 as a potential therapeutic target to delay neurodegeneration.