The cholinergic dysfunction in diabetic encephalopathy: role of pro-nerve growth factor and effects of electroacupuncture

The thesis deals with the effects and mechanisms of electroacupuncture therapy on hippocampal functional and molecular dysregulations induced in rats by early experimental diabetes. In the first part of the thesis, the candidate Marzia Soligo studied the impact of the early diabetic encephalopathy on the hippocampal physiology, in particular targeting the alterations of pro-nerve growth factor (proNGF) secretion, the functionality of muscarinic receptors M1 and M2 subtypes and the effects of electroacupuncture in counteracting the diabetes-induced dysregulations. The data obtained have been published in two referenced papers and indicate that the development and progression of diabetes generate a mild cognitive impairment reducing the functions of the septo-hippocampal cholinergic circuitry, depressing neural plasticity and inducing proNGF accumulation in the brain. Furthermore, the data demonstrate that the physical therapy, electroacupuncture, probably normalizing the altered M1-AChR functionality, counteracts the diabetes-induced deleterious effects on hippocampal physiology by ameliorating hippocampal-related memory functions, recovering the impaired long-term potentiation at the dentate gyrus (DG-LTP) and normalizing the activity-dependent release of proNGF. Therefore, it was hypothesized that a physical therapy based on repetitive sensory stimulation could promote hippocampal neural activity and conceivably improve the diabetes-induced cognitive impairment, in turn regulating the metabolism of key trophic factors such as proNGF/mNGF. In the second part of the thesis, the candidate focused her attention on the role that proNGF played on the hippocampal physiology, shifting the attention to the balance between the two relative parts of the total proNGF (proNGF-A and proNGF-B). The data suggested a differential modulation of the two proNGFs and a selective challenge of the proNGF-B to the pro-apoptotic receptor complex p75NTR/sortilin in diabetic animals, which were normalized by electroacupuncture. Based on these evidences, the candidate analysed the impact that alteration in the physiological balance between the two main proNGF protein variants, obtained by treatments with purified proNGF variants, could have in vitro and in normal and degenerating diabetic brain. The data obtained suggest that proNGF-B is the protein variant responsible for the observed neurodegenerative changes and that electroacupuncture effects could relies on the normalization of the proNGF-A/B balance in diabetic brain. The candidate suggests, based on her overall observation, a novel and intriguing update of the actual model for the proNGF metabolism. Moreover, she obtained evidence for the existence of the predicted proNGF longer splicing variant (proNGF-A) in rat tissues, by a novel RT-PCR assay.