title: Tissue-nonspecific alkaline phosphatase acts redundantly with PAP and NT5E to generate adenosine in the dorsal spinal cord.
abstract: Prostatic acid phosphatase (PAP) and ecto-5'-nucleotidase (NT5E) hydrolyze extracellular AMP to adenosine in dorsal root ganglia (DRG) neurons and in the dorsal spinal cord. Previously, we found that adenosine production was reduced, but not eliminated, in Pap⁻/⁻/Nt5e⁻/⁻ double knock-out (dKO) mice, suggesting that a third AMP ectonucleotidase was present in these tissues. Here, we found that tissue-nonspecific alkaline phosphatase (TNAP, encoded by the Alpl gene) is expressed and functional in DRG neurons and spinal neurons. Using a cell-based assay, we found that TNAP rapidly hydrolyzed extracellular AMP and activated adenosine receptors. This activity was eliminated by MLS-0038949, a selective pharmacological inhibitor of TNAP. In addition, MLS-0038949 eliminated AMP hydrolysis in DRG and spinal lamina II of dKO mice. Using fast-scan-cyclic voltammetry, we found that adenosine was rapidly produced from AMP in spinal cord slices from dKO mice, but virtually no adenosine was produced in spinal cord slices from dKO mice treated with MLS-0038949. Last, we found that AMP inhibited excitatory neurotransmission via adenosine A1 receptor activation in spinal cord slices from wild-type, Pap⁻/⁻, Nt5e⁻/⁻, and dKO mice, but failed to inhibit neurotransmission in slices from dKO mice treated with MLS-0038949. These data suggest that triple elimination of TNAP, PAP, and NT5E is required to block AMP hydrolysis to adenosine in DRG neurons and dorsal spinal cord. Moreover, our data reveal that TNAP, PAP, and NT5E are the main AMP ectonucleotidases in primary somatosensory neurons and regulate physiology by metabolizing extracellular purine nucleotides.
authors.affiliation: Department of Cell Biology and Physiology, and Department of Chemistry, Neuroscience Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Street
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Kramer
authors.forename: Paul L
authors.initials: PL
authors.lastname: Walsh
authors.forename: Bonnie
authors.initials: B
authors.lastname: Taylor-Blake
authors.forename: Manisha C
authors.initials: MC
authors.lastname: Yadav
authors.forename: Ian F
authors.initials: IF
authors.lastname: King
authors.forename: Pirkko
authors.initials: P
authors.lastname: Vihko
authors.forename: R Mark
authors.initials: RM
authors.lastname: Wightman
authors.forename: José Luis
authors.initials: JL
authors.lastname: Millán
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Zylka
mesh_terms: D015720:5'-Nucleotidase / Q000378:metabolism*; D000135:Acid Phosphatase; D000241:Adenosine / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D058851:GPI-Linked Proteins / Q000378:metabolism; D005727:Ganglia, Spinal / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D013116:Spinal Cord / Q000737:chemistry / Q000378:metabolism; D014018:Tissue Distribution / Q000502:physiology
chemical_list: D058851:GPI-Linked Proteins; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; C428439:prostatic acid phosphatase; D017027:Protein Tyrosine Phosphatases; D015720:5'-Nucleotidase; C548242:Nt5e protein, mouse; D000241:Adenosine