Investigating properties of cerebro-spinal fluid contacting cells in rodents; can they influence ependymal cell proliferation?

The spinal cord is part of the central nervous system which contributes to many physiological functions. There is a possible neurogenic niche located within the central canal of the spinal cord, within which there are a subtype of cells proliferating at baseline. These cells demonstrate plasticity via an increased rate of proliferation following spinal cord injury (SCI). Neighbouring these dividing cells are cerebro-spinal fluid contacting cells (CSFcCs) which have a poorly defined function within rodents. This study assesses properties of CSFcCs, validates a novel transgenic mouse line and uses viral tracing to demonstrate the length and direction of their extensions. It also assessed whether CSFcCs can be manipulated to influence the activity of the cells proliferating within the ependymal layer.
Antibody labelling revealed CSFcCs also labelled with GCaMP6f expressed by the vesicular gamma-aminobutyric acid transporter (VGAT) promoter and a synaptic vesicle protein revealing they have the apparatus to load GABA into vesicles and release vesicular content from their terminals within the central canal (CC). They also co-labelled with an antibody to the glucagon-like peptide 1 receptor (GLP1R), offering a novel input for stimulation.
Intraperitoneal injection of the GLP1R agonist liraglutide with the proliferative marker 5- ethynyl-2'-deoxyuridine (EdU) resulted in a reduced number of EdU positive cells in the ependymal cell layer (ECL), compared to mice with EdU and vehicle only injections. This suggests there is a relationship between CSFcCs and ependymal cells (EpCs) which has not previously been shown.
Mice expressing cre-recombinase under control of the PKD2L1 promoter, which are shown here to be specifically expressed in CSFcCs in the CNS, were intraspinally injected with a floxed virus expressing diphtheria toxin subunit-A (DTA). There was a remarkable increase in the number of EdU+ cells around the CC in most regions of the spinal cord compared to uninjected mice or mice injected with a virus that did not express DTA. Markers of cell death indicated that the expression of DTA in CSFcCs resulted in the death of EpCs, further indicating an essential trophic relationship between these cells.
This connection between CSFcCs and dividing ependymal cells (EpCs) may be utilised for therapeutic benefit in disorders of the spinal cord where modulating proliferation may be used to restore cell populations.