Cholinergic impact on neuroplasticity drives muscarinic M1 receptor mediated differentiation into neurons

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Cholinergic signaling of muscarinic receptors directly involves in the neuroprotection of muscone by inducing Ca2+ antagonism and maintaining mitochondrial function

ETHNOPHARMACOLOGICAL RELEVANCE

Musk, a traditional Chinese medicine, is broadly used in inducing resuscitation and refreshing the mind, activating blood and alleviating pain. It is commonly used for the treatment of ischemic stroke, and muscone is its core medicinal component.

AIM OF THE STUDY

The aim of this study was to explore whether muscone ameliorates neuronal damage through cholinergic signaling of muscarinic receptors.

MATERIALS AND METHODS

The effects of muscone were tested in a rat model of middle cerebral artery occlusion (MCAO) as well as injured neurons induced by oxygen-glucose deprivation (OGD) in PC12 cells. Cell counting kit 8 (CCK8) assay was used to measure the cell viability, and the production of lactate dehydrogenase (LDH) and adenosine-triphosphate (ATP) were examined by kit. 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA), tetramethylrhodamine ethyl ester (TMRE) and Fluo-4 acetoxymethyl ester (Fluo-4 AM) staining were used to demonstrate effect of muscone on the reactive oxygen species (ROS) level, mitochondria membrane potential (MMP) and intracellular Ca2+ measurement in cells respectively, in which all of those staining was visualized by laser confocal microscope. For in vivo experiments, rats' cerebral blood flow was measured using laser Doppler blood flowmetry to evaluate the MCAO model, and a modified neurological severity score (mNSS) was used to assess the recovery of neurological function. Calculate infarct rate was measured by 2,3,5-Triphenyl Tetrazolium Chloride (TTC) staining. Except DCFH-DA and Fluo-4 AM staining, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl benzimidazolylcarbocyanine iodide (JC-1) staining was used to observe intracellular Ca2+ measurement in brain cells. Protein levels in cells and tissues were detected by Western blot.

RESULTS

Pretreatment with muscone significantly improved the cell viability, lactic acid production, mitochondrial membrane potential collapse and function, Ca2+ overload, ROS generation, and cell apoptosis in OGD PC12 cells. Muscone also regulated PI3K, ERK and AKT signal pathways by activating cholinergic signaling of muscarinic receptors in PC12 cells induced with OGD. More importantly, the blocking of cholinergic signaling of muscarinic receptors by atropine significantly reduces the neuroprotective effects of muscone, including the cell viability, Ca2+ efflux, and mitochondrial repair. Furthermore, muscone was found to effectively alleviate mitochondrial dysfunction and elevated levels of ROS induced by the MCAO in the brain tissue. Notably, this beneficial effect of muscone was attenuated by atropine but not by (+)-Sparteine.

CONCLUSIONS

Our study indicates that muscone exerts its neuroprotective effects by activating muscarinic receptors of cholinergic signaling, thus providing a promising therapeutic target for the treatment of OGD-induced nerve injury in stroke. The findings suggest that these treatments may hold potential benefits for stroke patients.

Differentiation of human glioblastoma U87 cells into cholinergic neuron

To facilitate research methodologies for investigating the role of cholinergic nerves in many diseases, establishing an in vitro cholinergic neuron model is necessary. In this study, we investigated whether human glioblastoma U87 cells could be differentiated into cholinergic neurons in vitro. Sodium butyrate was used as the differentiation agent. The differentiated cells established by inducing U87 cells with sodium butyrate were named D-U87 cells. Immunofluorescence was used to label the neuronal markers MAP2, NF-M, and ChAT and the glial marker GFAP in D-U87 cells. Flow cytometry was used to measure cell cycle distribution in D-U87 cells. PCR, protein chip, and western blot assays were used to measure the expression levels of muscarinic cholinergic receptor 1 (M1), M4, ChAT, SYP and Akt. ELISA was used to measure neurotransmitter levels. As a result, we found that sodium butyrate induced U87 cell differentiation into cells with neuronal characteristics and increased not only the expression levels of the cholinergic neuron-related proteins M1, M4, ChAT and SYP in D-U87 cells but also the acetylcholine neurotransmitters in D-U87 cells. Moreover, the Akt protein expression in D-U87 cells was increased compared with that in U87 cells. Finally, we found that M1, M4, ChAT and SYP protein expression and acetylcholine secretion levels were significantly decreased in D-U87 cells after treatment with the Akt inhibitor MK-2206. These results demonstrate that D-U87 cells exhibit cholinergic neuron characteristics and that sodium butyrate induced U87 cell differentiation into cholinergic neuron partially through Akt signaling.

Effects of muscarinic acetylcholine receptor stimulation on the differentiation of mouse induced pluripotent stem cells into neural progenitor cells

Muscarinic acetylcholine receptors (mAchRs), which are expressed in various embryonic cells, may regulate neuronal differentiation. In the present study, we examined the effects of mAchR stimulation on the differentiation of mouse induced pluripotent stem (iPS) cells into neural progenitor cells (NPCs). Mouse iPS cells were cultured on ultra-low attachment dishes to induce embryoid body (EB) formation. All-trans retinoic acid (ATRA, 3 μmol/L) and/or pilocarpine (10 or 100 μmol/L), a mAchR agonist, were added to EB cultures for 4 days, following which the EBs were cultured on gelatin-coated plates for 7 days. Subtype-specific antibody staining revealed that mouse iPS cells predominantly express m₂ - and m₄ -AchR. Treatment with pilocarpine alone did not affect the expression of Nestin (a specific marker for neural progenitor cells). However, additional treatment with pilocarpine significantly suppressed ATRA-induced Nestin expression. Pretreating EBs with either AF-DX116 (an antagonist of both m₂ - and m₄ -AchR) or forskolin (an activator of adenylate cyclase) significantly reversed the pilocarpine-induced suppression of Nestin expression. In addition, treatment with pilocarpine significantly suppressed ATRA-induced phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB). These findings suggest that the stimulation of m₂ - or m₄ -AchR suppresses ATRA-induced differentiation of mouse iPS cells into NPCs by inhibiting the cAMP/protein kinase A pathway and CREB activation.

Lamin A/C Is Required for ChAT-Dependent Neuroblastoma Differentiation

The mouse neuroblastoma N18TG2 clone is unable to differentiate and is defective for the enzymes of the biosynthesis of neurotransmitters. The forced expression of choline acetyltransferase (ChAT) in these cells results in the synthesis and release of acetylcholine (Ach) and hence in the expression of neurospecific features and markers. To understand how the expression of ChAT triggered neuronal differentiation, we studied the differences in genome-wide transcription profiles between the N18TG2 parental cells and its ChAT-expressing 2/4 derived clone. The engagement of the 2/4 cells in the neuronal developmental program was confirmed by the increase of the expression level of several differentiation-related genes and by the reduction of the amount of transcripts of cell cycle genes. At the same time, we observed a massive reorganization of cytoskeletal proteins in terms of gene expression, with the accumulation of the nucleoskeletal lamina component Lamin A/C in differentiating cells. The increase of the Lmna transcripts induced by ChAT expression in 2/4 cells was mimicked treating the parental N18TG2 cells with the acetylcholine receptor agonist carbachol, thus demonstrating the direct role played by this receptor in neuron nuclei maturation. Conversely, a treatment of 2/4 cells with the muscarinic receptor antagonist atropine resulted in the reduction of the amount of Lmna RNA. Finally, the hypothesis that Lmna gene product might play a crucial role in the ChAT-dependent molecular differentiation cascade was strongly supported by Lmna knockdown in 2/4 cells leading to the downregulation of genes involved in differentiation and cytoskeleton formation and to the upregulation of genes known to regulate self-renewal and stemness.

Acetylcholine secretion by motor neuron-like cells from umbilical cord mesenchymal stem cells

Umbilical cord mesenchymal stem cells were isolated by a double enzyme digestion method. The third passage of umbilical cord mesenchymal stem cells was induced with heparin and/or basic fibroblast growth factor. Results confirmed that cell morphology did not change after induction with basic fibroblast growth factor alone. However, neuronal morphology was visible, and microtubule-associated protein-2 expression and acetylcholine levels increased following induction with heparin alone or heparin combined with basic fibroblast growth factor. Hb9 and choline acetyltransferase expression was high following inductive with heparin combined with basic fibroblast growth factor. Results indicate that the inductive effect of basic fibroblast growth factor alone was not obvious. Heparin combined with basic fibroblast growth factor noticeably promoted the differentiation of umbilical cord mesenchymal stem cells into motor neuron-like cells. Simultaneously, umbilical cord mesenchymal stem cells could secrete acetylcholine.