In vivo and in vitro neurogenesis in human olfactory epithelium

Abstract

The birth and differentiation of neurons have been extensively studied in the olfactory epithelium (OE) of rodents but not in humans. The goal of this study was to characterize cellular composition and molecular expression of human OE in vivo and in vitro. In rodent OE, there are horizontal basal cells and globose basal cells that are morphologically and functionally distinct. In human OE, however, there appears to be no morphological distinction among basal cells, with almost all cells having round cell bodies similar to rodent globose basal cells. Unlike the case in rodents, human basal cells, including putative neuronal precursors, express p75NGFR, suggesting a distinctive role for p75NGFR in human OE neurogenesis. Molecular expression of neuronal cells during differentiation in human OE grossly follows that in rodents. However, the topographical organization of immature and mature ORNs in human OE differs from that of rodents, in that immature and mature ORNs in humans are dispersed throughout the OE, whereas rodent counterparts have a highly laminar organization. These observations together suggest that the birth and differentiation of neuronal cells in human OE differ from those in rodents. In OE explant culture, neuronal cells derived from human OE biopsy express markers for immature and mature neurons, grossly recapitulating neuronal differentiation of olfactory neurons in vivo. Furthermore, small numbers of cells are doubly label for bromodeoxyuridine and olfactory marker protein, indicating that neuronal cells born in vitro reach maturity. These data highlight species-related differences in OE development and demonstrate the utility of explant culture for experimental studies of human neuronal development.

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“…59-61 MAP-1B and NCAM identify dendrites and axons of ORNs and label nerve bundles intensely. 53 Carnosine-like immunoreactivity has also been demonstrated in ORNs. 62 Sustentacular Cells Sustentacular cells are irregular columnar cells with large vertically elongated euchromatic nuclei and multiple long microvilli.…”

“…In the human, however, there appears to exist only one basal cell type that morphologically resembles the GBCs in the rat. 53 These cells are usually 5 to 7 µm in diameter and have a rough cellular surface upon examination by electron microscopy. 46 Intermediate filament proteins have been markers of interest in the past.…”

“…108,109 Using a bank of antibodies, Doyle et al 110 found that nestin is actually expressed in the axonal ends and inferior processes of OE sustentacular cells in the basal compartment of the epithelium. Hahn et al 53 further investigated the expression of cytokeratin-5, another class of intermediate filament proteins, in human OE, but disappointingly, the staining showed that cytokeratin is expressed not only in the first layer of basal cells closest to the basal lamina but also in the cells above them.…”

“…53 The limitation of this marker is that 20% of the labeled cells reside in layers above the basal one, and not all cells positive for Ki-67 are positive for p75NGFR, a protein known to be expressed in basal cells as well as OECs. 53,111,112 Currently, there is still no known marker that exclusively labels human OE stem cells.…”

Techniques and devices to restore cognition

“…Neural stem cells acquired from biopsy of the olfactory epithelium or the ependymal lining may be cultured and grown on a patterned culture media to recreate functional neural circuits. Recent work has shown it is possible to biopsy the human olfactory epithelium and culture neural progenitors in vitro [50]. Neural progenitors derived from human olfactory epithelium may also be coaxed to form neurospheres which in turn can lead to autologous transplantation where minimal donor material can be isolated and expanded ex vivo [92].…”