BVRINSULINAD · BILIVERDIN REDUCTASE-A IN BRAIN INSULIN SIGNALING AND OXIDATIVE STRESS- MEDIATED NEURODEGENERATION

BILIVERDIN REDUCTASE-A IN BRAIN INSULIN SIGNALING AND OXIDATIVE STRESS- MEDIATED NEURODEGENERATION

Epidemiological data show the incidence of AD increases with age and doubles every 5 years after 65 years of age with 1275 new cases/100000 persons/year. The Alzheimer Association points out that the financial, emotional, and family costs for care of AD patients are enormous and will increase markedly in the near future in the absence of a therapeutic modality to slow or stop onset. From a pathological point of view, in different clinical studies, an association of T2DM and neurodegenerative disorders as well as decline in memory has been described. Interestingly, post-mortem analyses of Alzheimer disease (AD) subjects demonstrated insulin resistance in the brain proposing a role for cognitive deficits observed in AD. However, the mechanisms responsible for the onset of brain insulin resistance (BIR) need further elucidations. Biliverdin reductase-A (BVR-A) emerged as a unique Ser/Thr/Tyr kinase directly involved in the regulation of insulin signaling. Indeed, once activated via Tyr phosphorylation by insulin receptor (IR), BVR-A is able to phosphorylate the insulin receptor substrate (IRS)-1 on inhibitory domains, thus representing an upstream regulator in the insulin signaling cascade. Because we previously demonstrated the oxidative/nitrosative stress (OS/NS)-induced impairment of BVR-A in human Alzheimer disease (AD) brain, here we hypothesize that BVR-A dysregulation could be associated with the onset of BIR in AD. To this aim three research objectives (RO) have been completely addressed during these two-years project: • RO1. It has been tested the hypothesis that insulin resistance is associated with elevated oxidative/nitrosative stress (OS/NS) levels in brain of 3xTg-AD mice model of AD, and that these changes are associated with age, Abeta levels and aggregation state, and posttranslational modification of insulin signaling machinery. • RO2. It has been tested the hypothesis that insulin resistance in the brain of 3xTg-AD mice is associated with changes of BVR-A posttranslational modifications and functions. • RO3. It has been tested the hypothesis that intranasal insulin (INI) administration improves BVR-A functions and Abeta-mediated neuropathology in the brain of 3xTg-AD, and that these changes are associated with improved cognition. The same end points as those of Specific Aims 1 and 2 in insulin- or vehicle-treated mice will be determined. The work has been performed at the Department of Biochemical Sciences “A. Rossi-Fanelli” of Sapienza University of Rome, which provided all the specific expertises and facilities for the realization of the project in terms of both research and training acitviities. The results obtained highlighted two distinct phases in the hippocampus of 3xTg-AD mice: a first insulin signaling hyper-activation (3-6 months) followed by a persistent IRS1 inihibition and thus insulin resistance at both 12 and 18 months. In this picture, we found that BVR-A levels and activation start to decline early, at 6 months of age, prior the accumulation of Abeta and tau pathology, and remain persistently reduced until 18 months, possibly because the increased OS/NS levels in the same time-frame. In addition, because TNF-alpha is known to inhibit BVR-A promoter activity and TNF-alpha has been also demonstrated to be a conceivable mediator of BIR in AD, we wondered to check whether reduced BVR-A levels were associated with changes of TNF-alpha. Interestingly, an increase of TNF-alpha levels is evident only at 18 months, thus highlighting the impairment of BVR-A as an early event in the onset of BIR. Similar changes have been found during the normal ageing process in WT mice, but later in life. Experiments on SH-SY5Y cells further confirmed that either lack of BVR-A or OS/NS-induced impairment of BVR-A promotes BIR. Finally, we identified the sustained activation of mTOR, as one of the feedback mechanisms leading to insulin resistance following BVR-A impairment both in mice and cells. In a subsequent set of experiments, both WT and 3xTg-AD mice have been treated with insulin administered via the intranasal route to try to recover BVR-A activity and thus prevent insulin resistance. The results are strongly encouraging and will be published soon. To summarize, this project propose a novel mechanism for which: OS/NS-induced impairment of BVR-A is firstly responsible for a sustained activation of IRS1, which then causes the stimulation of negative feedback mechanisms (i.e. mTOR) aimed to turn-off IRS1 hyper-activity and thus insulin resistance. Similar alterations characterize the normal ageing process in mice, positing BVR-A impairment as a possible bridge in the transition from normal ageing to AD. In light of these results positing BVR-A as an early event in the onset of BIR, the rescue of BVR-A activity would represent a conceivable therapeutic strategy to prevent insulin resistance in AD. In conclusion, the results obtained in this project could have a potential socio-economic impact in the next future because by pharmacologically target BVR-A it would be possible to delay the progression of AD neuropathology. Indeed, the care of patients with AD requires an amount of financial resources which is increasing dramatically in Europe and in the world. Thus, AD represents not only a medical problem but also a big financial problem. In this regard the efforts of the European Community to promote and increment research on AD were and will be very strong, especially in light of the fact that it was estimated that delaying the onset of AD by 5 years would decrease its prevalence by 50%. The relevance of this project with regard to the role of BVR-A in AD pathogenesis stands on the proposal of a new target of intervention. The prominent position of BVR-A in the insulin pathway, indeed makes this protein of great interest for further researches.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз