Distribution of the high-affinity binding site and intracellular target of botulinum toxin type A in the human bladder.
BACKGROUND
Botulinum toxin type A (BoNTA) has been successfully used in the treatment of refractory detrusor overactivity. The toxin is internalized after binding a high-affinity receptor, synaptic vesicle protein 2 (SV2), which is exposed in the cell membrane during the exocytosis process. In the cytoplasm, BoNTA cleaves specific sites of synaptosomal-associated protein 25 (SNAP-25), preventing the assembly of the synaptic fusion complex SNARE and blocking exocytosis.


OBJECTIVE
In the present work, the distribution of SV2 and SNAP-25 was first investigated in human bladders. The neurochemistry of BoNTA-sensitive structures was then investigated using markers for parasympathetic, sympathetic, and sensory fibers.


METHODS
Human bladders were obtained from cadaveric organ donors (age range: 19-74 yr).


METHODS
Bladder sections were processed for single or dual immunofluorescence staining with antibodies against SV2, SNAP-25, β-3 tubulin, vesicular acetylcholine transporter, tyrosine hydroxilase, and calcitonin gene-related peptide.


CONCLUSIONS
SV2 and SNAP-25 immunoreactive fibers were distributed throughout the suburothelium and muscular layer. Double labeling showed extensive colocalization of both proteins in nerve fibers. SV2 is more expressed in parasympathetic fibers than in sympathetic or sensory fibers. No expression was found in urothelial or muscular cells. Because only normal bladders were used, this distribution should be applied with caution to pathologic bladders.


CONCLUSIONS
SV2 and SNAP-25 colocalize abundantly throughout the urinary bladder. SV2 is more abundant in cholinergic, parasympathetic fibers. These nerves are suggested to be the main target for BoNTA action in the human urinary bladder.
Coelho
Ana
A
Institute of Histology and Embriology, Faculty of Medicine, Alameda Prof. Hernani Monteiro, 4200-319 Porto, Portugal.
Dinis
Paolo
P
Pinto
Rui
R
Gorgal
Tiago
T
Silva
Carlos
C
Silva
André
A
Silva
João
J
Cruz
Célia D
CD
Cruz
Francisco
F
Avelino
António
A
D000328:Adult; D000368:Aged; D001665:Binding Sites; D019274:Botulinum Toxins, Type A / Q000378:metabolism*; D002102:Cadaver; D006801:Humans; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000378:metabolism*; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000032:analysis* / Q000378:metabolism*; D009498:Neurotoxins / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000032:analysis* / Q000378:metabolism*; D001743:Urinary Bladder / Q000737:chemistry*; D055815:Young Adult
D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; D050825:Synaptosomal-Associated Protein 25; C076414:SV2A protein, human; D019274:Botulinum Toxins, Type A