Alpha-7 Nicotinic Receptor Dampens Murine Osteoblastic Response to Inflammation and Age-Related Osteoarthritis

Abstract

IntroductionOsteoarthritis (OA) is a whole-joint disease characterized by a low-grade inflammation that is involved in both cartilage degradation and subchondral bone remodeling. Since subchondral bone has a cholinergic innervation and that acetylcholine (Ach) might have an anti-inflammatory effect through the α7 nicotinic Ach receptor (α7nAchR), we aimed (i) to determine the expression of non-neuronal cholinergic system and nicotinic receptor subunits by murine and human osteoblasts, (ii) to address the role of α7nAchR in osteoblastic response to inflammation, and (iii) to study the role of α7nAchR in a spontaneous aging OA model.MethodsPrimary cultures of WT and α7nAchR knock-out mice (Chrna7-/-) murine osteoblasts and of subchondral bone human OA osteoblasts were performed. The expressions of the non-neuronal cholinergic system and of the nAchR subunits were assessed by PCR. In vitro, IL1β-stimulated WT, Chrna7-/-, and human osteoblasts were pretreated with nicotine. At 24 h, expressions of interleukin-6 (IL6) and metalloproteinase-3 and -13 (MMP), RANK-ligand (RANKL), and osteoprotegerin (OPG) were quantified by qPCR and ELISA. Spontaneous aging OA was evaluated and compared between male WT and Chrna7-/- mice of 9 and 12 months.ResultsMurine WT osteoblasts express the main components of the cholinergic system and α7 subunit composing α7nAchR. Nicotine partially prevented the IL1β-induced expression and production of IL6, MMP3, and RANKL in WT osteoblasts. The effect for IL6 and MMP was mediated by α7nAchR since nicotine had no effect on Chrna7-/- osteoblasts while the RANKL decrease persisted. Chrna7-/- mice displayed significantly higher cartilage lesions than their WT counterparts at 9 and 12 months, without difference in subchondral bone remodeling. Human OA osteoblasts also expressed the non-neuronal cholinergic system and α7 subunit as well as CHRFAM7A, the dominant negative duplicate of Chrna7. Nicotine pretreatment did not significantly reduce IL6 and MMP3 production in IL-1β-stimulated human osteoarthritic osteoblasts (n = 4), possibly due to CHRFAM7A.ConclusionCholinergic system counteracts murine osteoblastic response to IL-1β through α7nAchR. Since α7nAchR deletion may limit cartilage degradation during murine age-related OA, enhancing cholinergic system could be a new therapeutic target in OA but may depend on CHRFAM7A expression.

Effects of CDP-choline on osteogenic differentiation of pre-osteoblastic MC3T3-E1 cells

“…The in ux of calcium through these receptors not only supports the mineralization of the bone matrix but also activates various intracellular signaling cascades, such as the Wnt/β-catenin pathway, which are essential for osteoblast differentiation and function. Thus, by engaging α7nAChRs, CDP-choline may enhance osteogenic differentiation through a mechanism that relies on the pivotal role of calcium signaling in bone health and regeneration (Courties et al 2022).…”

“…The expression of the cholinergic system in osteoblast-like cells has been associated with bone remodeling, with evidence suggesting that bone morphogenetic protein 2 (BMP-2) may regulate the cholinergic system in these cells during bone remodeling processes (En-Nosse et al 2009). Additionally, the α7 nicotinic acetylcholine receptor (α7nAchR) has been implicated in modulating the osteoblastic response to in ammation and age-related osteoarthritis, indicating a potential role for the cholinergic system in in ammatory processes affecting bone health (Courties et al 2020(Courties et al , 2022. Furthermore, the cholinergic signals in the bone marrow have been shown to impact hematopoietic stem cell quiescence during regenerative hematopoiesis, underscoring the broader regulatory role of the cholinergic system in bone marrow function (Serobyan et al 2007;Fielding et al 2022).…”

Osteoarthritis patients exhibit an autonomic dysfunction with indirect sympathetic dominance

“…HRV is mainly regulated by the parasympathetic vagus nerve [37] and consequently, OA patients seem to have a PNS deficiency that already occurs in the early stage of the disease. It is well known that PNS activation via the cholinergic signaling pathway exhibits anti-inflammatory effects in OA [38]. For example, human OA synovium and synoviocytes express the alpha7 nicotinic acetyl receptor (α7nAChR) that inhibits cytokine expression upon activation [39].…”

α7- and α9-Containing Nicotinic Acetylcholine Receptors in the Functioning of Immune System and in Pain

“…The co-expression of this gene with full-length α7 has dominant negative effects on ion channel function [ 186 , 187 , 188 ] and on the α7-nAChR-mediated control of exocytotic neurotransmitter release [ 189 ]. Through the regulation of the cholinergic anti-inflammatory pathway (reviewed in [ 177 , 190 ]), the CHRFAM7A gene expression level is linked to the severity of inflammatory-related pathologies, such as sepsis, osteoarthritis [ 191 , 192 ], cerebral ischemia/reperfusion injury, hypertrophic scars, COVID-19, inflammatory bowel disease [ 193 ], renal fibrosis [ 194 ] and pain, including neuropathic pain after spinal cord injury [ 195 ] and inflammatory pain due to osteoarthritis modeling [ 192 ].…”