Functional nicotinic and muscarinic receptors on mesenchymal stem cells

Acetylcholinesterase inhibitors and the risk of hip fracture in Alzheimer's disease patients: a case-control study

Recent studies have reported the presence of acetylcholine (ACh) receptor subtypes in bone tissue, and have demonstrated that inhibition of the ACh receptors has negative effects on bone mass and fracture healing capacity. However, little is known about the potential clinical effects that increased ACh signaling might have on bone. Accordingly, this study was designed to determine whether the use of acetylcholinesterase inhibitors (AChEIs), a group of drugs that stimulate ACh receptors and are used to treat Alzheimer's disease (AD), is associated with a decreased risk of hip fracture in AD patients. To accomplish this objective, a case-control analysis was performed using the AD population, aged above 75 years, based in the local health area of the Carlos Haya Hospital, in Malaga, Spain. The cases were 80 AD patients that suffered a hip fracture between January 2004 and December 2008. The controls were 2178 AD patients without hip fracture followed at our health care area during the same period of time. Compared with patients who did not use AChEIs, the hip fracture adjusted odds ratio (OR) for users of AChEIs was 0.42 (95% confidence interval [CI], 0.24-0.72), for users of rivastigmine was 0.22 (95% CI, 0.10-0.45), and for users of donepezil was 0.39 (95% CI, 0.19-0.76). Data were adjusted for the following parameters: body mass index, fall risk, smoking habits, cognition, dependence, degree of AD, comorbidity score, treatment with selective serotonin reuptake inhibitors, age, and gender. Our data suggests that use of AChEIs donepezil and rivastigmine is associated with a reduced risk of fractures in AD patients. Many elderly patients with AD disease who are at risk of developing osteoporosis may potentially benefit from therapy with the AChEIs donepezil and rivastigmine.

The musculoskeletal effects of perioperative smoking

Although the carcinogenic consequences of smoking are well known, further research is needed on the effects of smoking on musculoskeletal health and surgical outcomes. Orthopaedic perioperative complications of smoking include impaired healing, increased infection, delayed and/or impaired fracture union and arthrodesis, and inferior arthroplasty outcomes. The incorporation of smoking cessation protocols such as transdermal patches, chewing gum, lozenges, inhalers, sprays, bupropion, and varenicline in the perioperative period may result in substantial benefits for patients' musculoskeletal and general health.

Stressing hematopoiesis and immunity: an acetylcholinesterase window into nervous and immune system interactions

Hematopoietic stem cells (HSCs) differentiate and generate all blood cell lineages while maintaining self-renewal ability throughout life. Systemic responses to stressful insults, either psychological or physical exert both stimulating and down-regulating effects on these dynamic members of the immune system. Stress-facilitated division and re-oriented differentiation of progenitor cells modifies hematopoietic cell type composition, while enhancing cytokine production and promoting inflammation. Inversely, stress-induced increases in the neurotransmitter acetylcholine (ACh) act to mitigate inflammatory response and regain homeostasis. This signaling process is terminated when ACh is hydrolyzed by acetylcholinesterase (AChE). Alternative splicing, which is stress-modified, changes the composition of AChE variants, modifying their terminal sequences, susceptibility for microRNA suppression, and sub-cellular localizations. Intriguingly, the effects of stress and AChE variants on hematopoietic development and inflammation in health and disease are both subject to small molecule as well as oligonucleotide-mediated manipulations in vitro and in vivo. The therapeutic agents can thus be targeted to the enzyme protein, its encoding mRNA transcripts, or the regulator microRNA-132, opening new venues for therapeutic interference with multiple nervous and immune system diseases.

Nicotine promotes proliferation and collagen synthesis of chondrocytes isolated from normal human and osteoarthritis patients

The aims of the study were to show the direct effect of nicotine with different concentrations (0, 25, 50, and 100 ng/ml) on chondrocytes isolated from normal human and osteoarthritis patients, respectively. Microscopic observation was performed during the culture with an inverted microscope. Methyl thiazolyl tetrazolium (MTT) assay method was adopted to observe the influence of nicotine on the proliferation of chondrocytes, and real-time PCR and ELISA were used to assay the mRNA and protein expression of type II collagen and aggrecan, respectively. We discovered that the OA chondrocytes were similar to fibroblasts in shape and grow slower than normal chondrocytes. The proliferation of the two kinds of chondrocytes was increased in a concentration-dependent manner and in a time-dependent manner (P<0.05). Also, we found that the mRNA level of type II collagen were upregulated under 25-100 ng/ml nicotine doses both in the two kinds of chondrocytes compared with control. The expression of protein levels of type II collagen were synthesized in line with the increase in mRNA. No effect was observed on aggrecan synthesis with any nicotine dose. We concluded that nicotine has the same effect on both chondrocytes, obtained either from osteoarthritis patients or from normal human, and the positive effect of smoking in OA may relate to the alteration in metabolism of chondrocytes.

Expression of non-neuronal cholinergic system in osteoblast-like cells and its involvement in osteogenesis

Acetylcholine (ACh) is detected in a variety of non-neuronal cells where it acts as a para/autocrine signaling molecule controlling basic cell functions such as proliferation, differentation, and maintenance of cell-cell contacts. ACh-synthesizing enzymes include choline acetyltransferase and carnitine acetyltransferase (CarAT). ACh is released through vesicular exocytosis or directly from the cytoplasm via organic cation transporters (OCT). Extracellular ACh binds to nicotinic (nAChR) and muscarinic receptors (MR). Degradation of ACh is performed by acetylcholinesterase and butyrylcholinesterase (BChE). Here, we have determined whether these molecules are expressed in osteoblast-like cells, by means of reverse transcription polymerase chain reaction and immunohistochemistry, focusing on nAChR subunits alpha3 and alpha5. RNA for CarAT, OCT-1, M2R, M5R, nAChR subunits alpha3, alpha5, alpha9, alpha10, beta2, beta3, and BChE were detected in human (SAOS-2) and murine (MC3T3-E1) osteoblast-like cells. Other cholinergic components were only expressed species-specifically, e.g., M3R and nAChR subunit alpha7. Immunhistochemistry localized the nAChR subunits alpha3 and alpha5 in osteoblasts in vitro and in vivo where they were up-regulated after application of bone morphogenetic protein-2 (BMP-2) during fracture healing in a rat model. Thus, the cholinergic system of osteoblast-like cells might be regulated by BMP-2 during bone remodeling. Osteoblast-like cells express all necessary enzymes, transporters, and receptors for ACh synthesis and recycling.

Cholinergic receptor pathways involved in apoptosis, cell proliferation and neuronal differentiation

Acetylcholine (ACh) has been shown to modulate neuronal differentiation during early development. Both muscarinic and nicotinic acetylcholine receptors (AChRs) regulate a wide variety of physiological responses, including apoptosis, cellular proliferation and neuronal differentiation. However, the intracellular mechanisms underlying these effects of AChR signaling are not fully understood. It is known that activation of AChRs increase cellular proliferation and neurogenesis and that regulation of intracellular calcium through AChRs may underlie the many functions of ACh. Intriguingly, activation of diverse signaling molecules such as Ras-mitogen-activated protein kinase, phosphatidylinositol 3-kinase-Akt, protein kinase C and c-Src is modulated by AChRs. Here we discuss the roles of ACh in neuronal differentiation, cell proliferation and apoptosis. We also discuss the pathways involved in these processes, as well as the effects of novel endogenous AChRs agonists and strategies to enhance neuronal-differentiation of stem and neural progenitor cells. Further understanding of the intracellular mechanisms underlying AChR signaling may provide insights for novel therapeutic strategies, as abnormal AChR activity is present in many diseases.

Survival, neuron-like differentiation and functionality of mesenchymal stem cells in neurotoxic environment: the critical role of erythropoietin

Mesenchymal stem cells (MSCs) can ameliorate symptoms in several neurodegenerative diseases. However, the toxic environment of a degenerating central nervous system (CNS) characterized by hypoxia, glutamate (Glu) excess and amyloid beta (Abeta) pathology may hamper the survival and regenerative/replacing capacities of engrafted stem cells. Indeed, human MSC (hMSC) exposed to hypoxia were disabled in (i) the capacity of their muscarinic receptors (mAChRs) to respond to acetylcholine (ACh) with a transient increase in intracellular [Ca(2+)], (ii) their capacity to metabolize Glu, reflected by a strong decrease in glutamine synthetase activity, and (iii) their survival on exposure to Glu. Cocultivation of MSC with PC12 cells expressing the amyloid precursor protein gene (APPsw-PC12) increased the release of IL-6 from MSC. HMSC exposed to erythropoietin (EPO) showed a cholinergic neuron-like phenotype reflected by increased cellular levels of choline acetyltransferase, ACh and mAChR. All their functional deficits observed under hypoxia, Glu exposure and APPsw-PC12 cocultivation were reversed by the application of EPO, which increased the expression of Wnt3a. EPO also enhanced the metabolism of Abeta in MSC by increasing their neprilysin content. Our data show that cholinergic neuron-like differentiation of MSC, their functionality and resistance to a neurotoxic environment is regulated and can be improved by EPO, highlighting its potential for optimizing cellular therapies of the CNS.