title: Roles of lysosomal proteolytic systems in AQP5 degradation in the submandibular gland of rats following chorda tympani parasympathetic denervation.
abstract: Chorda tympani denervation (CTD) of rats was earlier shown to result in loss of submandibular gland (SMG) weight (at only 1 wk) and in continued reduction in aquaporin 5 (AQP5) protein expression (until 4 wk), without affecting its mRNA synthesis (Li X, Azlina A, Karabasil MR, Purwanti N, Hasegawa T, Yao C, Akamatsu T, Hosoi K. Am J Physiol Gastrointest Liver Physiol 295: G112-G123, 2008). The present study indicated that despite elevation of bax, a proapoptosis protein, by CTD, the operation also increased the level of bcl-2, an antiapoptosis protein, in the SMG. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL assay) showed no increase in the number of apoptotic cells in the SMG. CTD, however, induced strongly and transiently (at 1-3 days) the protein expression of LC3B-II, a marker protein of autophagosomes, suggesting that the reduction in the gland weight was due to onset of autophagy by CTD. Upon CTD, Lamp2, a lysosomal marker, gradually increased in amount, reaching a peak at the 14th day. Immunohistochemical analysis revealed an increase in the number of lysosome-like structures positive for both AQP5 and Lamp2 in the acinar cells of the SMG after CTD; similar changes were observed also for AQP5 and LC3Bs. These data suggest that AQP5 in the SMG entered autophagosomes and/or lysosomes for degradation upon CTD. In vitro AQP5-degrading activity was found in the SMG extracts, and such activity was shown to be increased by CTD. Inhibitor experiments implied cathepsins B and L to be candidate enzymes for this degradation under normal and CTD conditions, respectively.
authors.affiliation: Department of Molecular Oral Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Azlina
authors.forename: Purevjav
authors.initials: P
authors.lastname: Javkhlan
authors.forename: Yuka
authors.initials: Y
authors.lastname: Hiroshima
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Chenjuan
authors.initials: C
authors.lastname: Yao
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Akamatsu
authors.forename: Kazuo
authors.initials: K
authors.lastname: Hosoi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051402:Aquaporin 5 / Q000378:metabolism*; D015153:Blotting, Western; D002814:Chorda Tympani Nerve / Q000293:injuries*; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D052119:Lysosomal-Associated Membrane Protein 2 / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D017764:Parasympathectomy; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013363:Submandibular Gland / Q000294:innervation / Q000378:metabolism*
chemical_list: D051402:Aquaporin 5; D052119:Lysosomal-Associated Membrane Protein 2; D019253:Proto-Oncogene Proteins c-bcl-2