Developmentally regulated expression of ectonucleotidases NTPDase5 and NTPDase6 and UDP-responsive P2Y receptors in the rat cochlea

Abstract

Ectonucleoside triphosphate diphosphohydrolases (E-NTPDases) regulate complex extracellular P2 receptor signalling pathways in mammalian tissues by hydrolysing extracellular nucleotides to the respective nucleosides. All enzymes from this family (NTPDase1-8) are expressed in the adult rat cochlea. This study reports the changes in expression of NTPDase5 and NTPDase6 in the developing rat cochlea. These two intracellular members of the E-NTPDase family can be released in a soluble form and show preference for nucleoside 5'-diphosphates, such as UDP and GDP. Here, we demonstrate differential spatial and temporal patterns for NTPDase5 and NTPDase6 expression during cochlear development, which are indicative of both cytosolic and extracellular action via pyrimidines. NTPDase5 is noted during the early postnatal period in developing sensory hair cells and supporting Deiters' cells of the organ of Corti, and primary auditory neurons located in the spiral ganglion. In contrast, NTPDase6 is confined to the embryonic and early postnatal hair cell bundles. NTPDase6 immunolocalisation in the developing cochlea underpins its putative role in hair cell bundle development, probably via cytosolic action, whilst NTPDase5 may have a broader extracellular role in the development of sensory and neural tissues in the rat cochlea. Both NTPDase5 and NTPDase6 colocalize with UDP-preferring P2Y(4), P2Y(6) and P2Y(14) receptors during cochlear development, but this strong association was lost in the adult cochlea. Spatiotemporal topographic expression of NTPDase5 and NTPDase6 and P2Y receptors in adult and developing cochlear tissues provide strong support for the role of pyrimidinergic signalling in cochlear development.

Differential expression of P2Y receptors in the rat cochlea during development

“…Pharmacological profiling of the ATP and UTP mediated short-circuit current in the outer sulcus is consistent with a P2Y 2 or P2Y 4 receptor-mediated increase in cation uptake in addition to the P2X 2 receptor path [47,48]. P2Y 14 receptor expression also occurs in these regions postnatally [49]. The P2Y receptor-mediated cation return was prominent in the neonatal rat cochlea and downregulated to adult levels by the end of the second postnatal week [48].…”

Purinergic signalling during development and ageing

“…These cells exhibit spontaneous Ca 2+ waves activated by ATP [253] and may allow the establishment of the tonotopic organization of the cochlea and spiral ganglion cell innervation, although this is disputed [254]. Changes in expression of the ectonucleotidases, NTPDase5 and NTPDase6, and uridine diphosphate-activated P2Y 6 receptors were observed during rat cochlea development [255].…”

Purinergic Signaling and Cochlear Injury-Targeting the Immune System?

“…Among the metabotropic P2Y receptors [40,44,66,67,68,69,70], the P2Y4 subtype shows a widespread expression in all developmental stages, both in sensory [44,66,68,70] and in non-sensory cells [66,67,68,69,70]. Other P2Y subtypes detected in the cochlea are P2Y1, P2Y2, P2Y6 (e.g., rat and guinea pig OHC) [40,66,68] and P2Y12 (e.g., rat OHC) [66,68]. Functional data support the view that P2Y receptor subtypes are also present in supporting cells around hair cells [67,83,84,85].…”

“…These enzymes are also present in cochlea of hearing rodents, including their major representatives such as ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase1) and NTPDase3, known to terminate P2 receptor-mediated signal transmission (by hydrolyzing nucleotides), and NTPDase2 preferentially interconverting nucleotides (i.e., producing ADP from released ATP) [77,78,80,81]. NTPDase5 and NTPDase6, preferentially hydrolyzing nucleoside 5’-diphosphates, such as UDP and GDP, are present both in developing and mature hearing organ in rodents [68,82] (Table 3).…”