The distribution of apolipoprotein E in mouse olfactory epithelium

Abstract

Previous studies from our laboratory suggest that apolipoprotein (apoE), a lipid transporting protein, facilitates olfactory nerve regeneration. We have shown that apoE is enriched in the olfactory nerve and around the glomeruli of the olfactory bulb (OB). The studies reported herein were undertaken to identify possible sources of apoE in the olfactory epithelium (OE). Immunoblotting results revealed apoE expression in the OE of wild-type (WT) mice, but not in apoE deficient/knockout (KO) mice. Immunohistochemical studies revealed that the perikarya and processes of sustentacular (Sus) cells expressed apoE-like immunoreactivity. Minimal neuronal apoE immunostaining was seen, although apoE was observed in the interstial spaces between olfactory receptor neurons (ORN). Substantial apoE-like immunoreactivity was localized to the endfeet and terminal process of Sus cells surrounding the basal cells. Double labeling immunocytochemical studies confirmed that the cell bodies and endfeet of Sus cells expressed high levels of apoE. The endothelial cells of blood vessels were intensely stained for apoE in the lamina propria. Cells forming Bowman's gland also immunostained for apoE. The apoE staining in the nerve fascicles was less intense, but was uniformly distributed throughout the core of the nerve bundles. Heavily stained cells, probably ensheathing glia, surrounded the nerve fascicles. These results revealed that apoE is expressed in the adult OE and lamina propria at strategic locations where it could facilitate the differentiation, maturation and axonal growth of the ORN, perhaps by recycling lipids from degenerating ORN for use by growing axons.

Odor Identification Deficit as a Predictor of Five-Year Global Cognitive Change: Interactive Effects with Age and ApoE-ε4

“…The apolipoprotein E (ApoE) gene is expressed in olfactory brain structures and is believed to play a role in neuronal regenerative processes as well as in the development of AD, the most common form of dementia (Corder et al 1993;Nathan et al 2005Nathan et al , 2007Struble et al 1999). However, evidence is mixed regarding the relationship between ApoE-e4 and olfactory function in nondemented elderly, with some studies reporting negative effects of the ApoE-e4 allele on olfactory processing (Gilbert and Murphy 2004;Murphy et al 1998) and others reporting no effect (Graves et al 1999;Swan and Carmelli 2002).…”

Impact of apoE deficiency during synaptic remodeling in the mouse olfactory bulb

“…The data indicate that apoE deficiency in KO mice is associated with a delayed recovery of the glomerular area and a slower recovery in Syn concentration in the OB. Keywords apoE; synaptophysin; olfactory bulb; glia; olfactory nerve; glial proteins; transgenic mice Apolipoprotein E (apoE), a lipid transporting protein, is widely expressed in the primary olfactory pathway [6,12,13,23,25]. Previous studies from our laboratories and others have shown apoE expression in the olfactory nerve and around the glomeruli in the OB of adult mice [12,23].…”

“…Keywords apoE; synaptophysin; olfactory bulb; glia; olfactory nerve; glial proteins; transgenic mice Apolipoprotein E (apoE), a lipid transporting protein, is widely expressed in the primary olfactory pathway [6,12,13,23,25]. Previous studies from our laboratories and others have shown apoE expression in the olfactory nerve and around the glomeruli in the OB of adult mice [12,23]. ApoE levels in the OB were two fold higher than normal immediately following OE lesion, and remained elevated over a 3-week period when axons from the newly differentiated olfactory receptor neurons (ORN) grew to reestablish the synaptic connections with cells in the glomeruli [13].…”

Olfactory Function: The Influence of Demographic, Cognitive, and Genetic factors

“…The ApoE gene, which is expressed in the olfactory bulb and the olfactory epithelium, is associated with the continuous degeneration and regeneration processes that occur in the olfactory nerve (Nathan, Nannapaneni, Gairhe, Nwosu, & Struble, 2007;Struble, Short, Ghobrial, & Nathan, 1999). Also, severity of tau pathology in the olfactory bulb of AD correlates with the ApoE ɛ4 genotype (Tsuboi et al, 2003).…”