Influence of interferon-gamma on the differentiation of cholinergic neurons in rat embryonic basal forebrain and septal nuclei

BACKGROUND： Interferon-gamma （IFN-γ） can make neurons in basal forebrain and septal nuclei differentiate into cholinergic neurons by treating the cells in cerebral cortex of newborn rats, without the inhibition from IFN-γ antibody. The important effect of IFN-γ on the development and differentiation of neurons has been found by some scholars. OBJ EClIVE：To investigate whether IFN-γ has differentiational effect on cholinergic neurons in basal forebrain and septal nuclei, and make clear that the increased number of cholinergic neurons is resulted by cell differentiation or cell proliferation. DESIGN ： Controlled observation trial SETTING： Department of Cell Biology, Medical School, Beijing University MATERIALS： Sixty-eight female Wistar rats at embryonic 16 days, weighing 250 to 350 g, were enrolled in this study, and they were provided by the Experimental Animal Center, Medical School, Beijing University. IFN-γ was the product of Gibco Company. METHODS： This study was carried out in the Department of Cell Biology, Medical School, Beijing University and Daheng Image Company of Chinese Academy of Sciences during September 1995 to December 2002. The female Wistar rats at embryonic 16 days were sacrificed, and their fetuses were taken out. Primary culture of the isolated basal forebrain and septal nuclei was performed. The cultured nerve cells were assigned into 3 groups： control group （nothing added）, IFN-γ group（1×10^5 U/L interferon）, IFN-γ＋ IFN-γ antibody group （1 ×10^5 U/L IFN-γ ＋ IFN-γ antibody）. The specific marker enzyme （choline acetyl transferase） of cholinergic neuron was stained with immunohistochemical method. Choline acetyl transferase positive cells were counted, and ^14C-acetyl CoA was used as substrate to detect the activity of choline acetyl transferase, so as to reflect the differentiational effect of IFN-γ on cholinergic neuron in basal forebrain and septal nuclei. Flow cytometry was used to analyze cell circle and detect the proliferation of nerve cells. Nerve cells were marked with MAP2 and counted to evaluate the neuronal proliferation in basal forebrain and septal nuclei. MAIN OUTCOME MEASURES： Effect of interferon-γ on the number and activity of choline acetyl transferase-positive ceils in basal forebrain and septal nuclei as well as the effect on neuronal proliferation. RESULTS ： ① Nerve cells in the basal forebrain and septal nuclei of IFN-γ group grew well compared with control group.②The differentiation of cholinergic neurons： The number and activity of choline acetyl transferase positive cells in IFN-γ group were significantly higher than those in the control group [（49.30 ±4.92） /100 cells vs （7.50±1.58） /100 cells; （2 049.00±12.30） min^-1 vs （1 227.30±12.59） min^-1, p 〈 0.01], while there was no significant difference in the number and activity of choline acetyl transferase positive cells between IFN-γ ＋ IFN-γ antibody group and control group（P 〉 0.05）. ③The proliferation of cholinergic neurons： Cell percentage was 17.2% and 19.8% at S-stage, 6.2% and 6.1% at G2＋M stage in the control group and IFN-γ group respectively, without significant difference （P 〉 0.05）. CONCLUSION ： IFN-γ does not promote the neuronal proliferation in basal forebrain and septal nuclei, and the increased expression of cholinergic neurons is not resulted by the increase in the number of neurons, but its differentiation.

Impairment of the nerve growth factor pathway driving amyloid accumulation in cholinergic neurons the incipit of the Alzheimer's disease story?

The current idea behind brain pathology is that disease is initiated by mild disturbances of common physiological processes. Overtime, the disruption of the neuronal homeostasis will determine irreversible degeneration and neuronal apoptosis. This could be also true in the case of nerve growth factor （NGF） al- terations in sporadic Alzheimer＇s disease （AD）, an age-related pathology characterized by cholinergic loss, amyloid plaques and neurofibrillary tangles. In fact, the pathway activated by NGF, a key neurotrophin for the metabolism of basal forebrain cholinergic neurons （BFCN）, is one of the first homeostatic systems affected in prodromal AD. NGF signaling dysfunctions have been thought for decades to occur in AD late stages, as a mere consequence of amyloid-driven disruption of the retrograde axonal transport of neuro- trophins to BFCN. Nowadays, a wealth of knowledge is potentially opening a new scenario： NGF signaling impairment occurs at the onset of AD and correlates better than amyloid load with cognitive decline. The recent acceleration in the characterization of anatomical, functional and molecular profiles of early AD is aimed at maximizing the efficacy of existing treatments and setting novel therapies. Accordingly, the elucidation of the molecular events underlying APP metabolism regulation by the NGF pathway in the sep- to-hippocampal system is crucial for the identification of new target molecules to slow and eventually halt mild cognitive impairment （MCI） and its progression toward AD.

The promise of stem cells in the therapy of Alzheimer’s disease

Alzheimer’s disease(AD),a common neurodegenerative disorder associated with gradually to dramatic neuronal death,synaptic loss and dementia,is considered to be one of the most obscure and intractable brain disorders in medicine.Currently,there is no therapy clinically available to induce marked symptomatic relief in AD patients.In recent years,the proof-of-concept studies using stem cell-based approaches in transgenic AD animal models provide new hope to develop stem cell-based therapies for the effective treatment of AD.The degeneration of basal forebrain cholinergic neurons(BFCNs)and the resultant cholinergic abnormalities in the brain contribute substantially to the cognitive decline of AD patients.The approches using stem cell-derived BFCNs as donor cells need to be developed,and to provide proof of principle that this subtype-specific neurons can induce functional recovery of AD animal models.With the continuous scientific advances in both academic and industrial fields,the potentials of stem cells in cellular neuroprotection and cell replacement in vivo have been elucidated,and stem cell-based therapy for repairing degenerative brains of AD is promising.