Endogenous pH 6.0 β-Galactosidase Activity Is Linked to Neuronal Differentiation in the Olfactory Epithelium

The histochemical detection of β-galactosidase enzymatic activity at pH 6.0 (β-gal-pH6) is a widely used biomarker of cellular senescence in aging tissues. This histochemical assay also detects the presence of programmed cell senescence during specific time windows in degenerating structures of vertebrate embryos. However, it has recently been shown that this enzymatic activity is also enhanced in subpopulations of differentiating neurons in the developing central nervous system in vertebrates. The present study addressed the histochemical detection of β-gal-pH6 enzymatic activity in the developing postnatal olfactory epithelium in the mouse. This activity was detected in the intermediate layer of the olfactory epithelium. As development progressed, the band of β-gal-pH6 labeling in this layer increased in width. Immunohistochemistry and lectin histochemistry showed the β-gal-pH6 staining to be strongly correlated with the immunolabeling of the olfactory marker protein (OMP) that identifies mature olfactory sensory neurons. The cell somata of a subpopulation of differentiated olfactory neurons that were recognized with the Dolichos biflorus agglutinin (DBA) were always located inside this band of β-gal-pH6 staining. However, the β-gal-pH6 histochemical signal was always absent from the apical region where the cytokeratin-8 positive supporting cells were located. Furthermore, no β-gal-pH6 staining was found in the basal region of the olfactory epithelium where PCNA/pHisH3 immunoreactive proliferating progenitor cells, GAP43 positive immature neurons, and cytokeratin-5 positive horizontal basal cells were located. Therefore, β-gal-pH6 seems to be linked to neuronal differentiation and cannot be regarded as a biomarker of cellular senescence during olfactory epithelium development in mice.