Nicotinic Receptor Alpha7 Expression Identifies a Novel Hematopoietic Progenitor Lineage

Abstract

How inflammatory responses are mechanistically modulated by nicotinic acetylcholine receptors (nAChR), especially by receptors composed of alpha7 (α7) subunits, is poorly defined. This includes a precise definition of cells that express α7 and how these impact on innate inflammatory responses. To this aim we used mice generated through homologous recombination that express an Ires-Cre-recombinase bi-cistronic extension of the endogenous α7 gene that when crossed with a reporter mouse expressing Rosa26-LoxP (yellow fluorescent protein (YFP)) marks in the offspring those cells of the α7 cell lineage (α7lin+). In the adult, on average 20–25 percent of the total CD45+ myeloid and lymphoid cells of the bone marrow (BM), blood, spleen, lymph nodes, and Peyers patches are α7lin+, although variability between litter mates in this value is observed. This hematopoietic α7lin+ subpopulation is also found in Sca1+cKit+ BM cells suggesting the α7 lineage is established early during hematopoiesis and the ratio remains stable in the individual thereafter as measured for at least 18 months. Both α7lin+ and α7lin– BM cells can reconstitute the immune system of naïve irradiated recipient mice and the α7lin+:α7lin– beginning ratio is stable in the recipient after reconstitution. Functionally the α7lin+:α7lin– lineages differ in response to LPS challenge. Most notable is the response to LPS as demonstrated by an enhanced production of IL-12/23(p40) by the α7lin+ cells. These studies demonstrate that α7lin+ identifies a novel subpopulation of bone marrow cells that include hematopoietic progenitor cells that can re-populate an animal’s inflammatory/immune system. These findings suggest that α7 exhibits a pleiotropic role in the hematopoietic system that includes both the direct modulation of pro-inflammatory cell composition and later in the adult the role of modulating pro-inflammatory responses that would impact upon an individual’s lifelong response to inflammation and infection.

Nicotinic alpha 7 receptor expression and modulation of the lung epithelial response to lipopolysaccharide

“…Interstitial CD45 + and CD45 - cells were isolated using an autoMACS cell separator (Miltenyi Biotec). Isolated CD45 - fractions were routinely tested for purity (routinely 92–95%) and determined for viability which was routinely high (less than 3–5% 7-AAD (viability stain) positive [13,14]. …”

“…RNA from the CD45 - cell population was prepared from the microbead enriched cell fraction as described previously [13,14]. The concentration and purity of the RNA was determined with a ND-1000 Spectrophotometer (NanoDrop Technologies, Wilmington, DE).…”

Nicotinic ACh receptors as therapeutic targets in CNS disorders

“…Expression of α7 * receptors in these non-neuronal cells suggests a possible role in brain innate immunity, inflammation, and neuroprotection [31, 32]. Immune cell expression of α7 * receptors has been shown to modulate inflammatory responses by regulating the production of inflammatory cytokines and chemokines [33, 34]. …”

Anti-inflammatory role of microglial alpha7 nAChRs and its role in neuroprotection

“…Hence, different technical approaches should be performed to ensure the validity of nAChR expression profiles observed in brain tissue. A good example of this could be the use of a novel transgenic a7 reporter to identify cell lineages of a7 expression in different type of cells [22].…”