Objective: Numerous epidemiological studies have demonstrated that vascular risk factors including diabetes mellitus (DM) increase the risk of developing Alzheimer's disease (AD). However, the mechanisms underlying the pathological relationship between DM and AD remain largely unknown. Tau is a microtubuleassociated protein that is predominantly expressed in the axons of neurons. More than 80 residues of tau can be potentially phosphorylated. Accumulation of hyperphosphorylated tau protein plays a role in neurodegeneration and cognitive impairment in patients with AD. Here, we developed a unique diabetic AD mouse model and analyzed behavioral phenotypes and biochemical changes occurring in the brain to investigate the impact of DM on tau pathology.Design and method: Tau-tg and WT mice were fed with either normal chow diet (NCD; 12% kcal fat, n = 9) or high-fat diet (HFD; 60% kcal fat, n = 10) from the age of one and a half to nine months. Metabolic parameters and behavioral phenotypes were assessed at eight months of age. Mice were then sacrificed at nine months of age and brains were analyzed histologically and biochemically. A quantitative proteomic analysis of protein phosphorylation was performed using brain extracts of tau-tg mice.Results: Tau-tg mice fed with HFD (HFD tau-tg) showed severe obesity and hyperinsulinemia compared with tau-tg mice fed with NCD (NCD tau-tg) (p < 0.01), with slight elevation of plasma glucose levels. HFD tau-tg showed exacerbation of motor impairments and decrement of habituation to novel environment. Histological analysis showed a significant decrease in the number of neurons in HFD tau-tg compared to NCD tau-tg. The amount of aggregated form of phospho-tau (Ser396) was increased in HFD tau-tg brain. Comprehensive phosphoproteomic analysis identified 11 phosphosites of tau significantly hyperphosphorylated in the brain of HFD tau-tg (p < 0.05).Conclusions: These results suggest that diabetic conditions such as obesity and hyperinsulinemia with minimal hyperglycemia exacerbate behavioral deficits in AD via hyperphosphorylation of tau protein. We identified specific phosphosites of tau involved in pathological relationship between DM and AD.

The zona glomerulosa of the adrenal gland is responsible for the synthesis and release of the mineralocorticoid aldosterone. This steroid hormone regulates salt reabsorption in the kidney and blood pressure. The most important stimuli of aldosterone synthesis are the serum concentrations of angiotensin II and potassium. In response to these stimuli, voltage and intracellular calcium levels in the zona glomerulosa oscillate, providing the signal for aldosterone synthesis. It was proposed that the voltage-gated T-type calcium channel CaV3.2 is necessary for the generation of these oscillations. However, Cacna1h knockout mice have normal plasma aldosterone levels, suggesting additional calcium entry pathways. We used a combination of calcium imaging, patch clamp and RNA sequencing to investigate such pathways in the murine zona glomerulosa. Cacna1h-/- glomerulosa cells showed similar calcium levels as wild-type mice in response to stimulation with angiotensin II or potassium. No calcium channels or transporters were upregulated to compensate for the loss of CaV3.2. The calcium oscillations observed in the zona glomerulosa of Cacna1h-/- mice were instead dependent on L-type voltage-gated calcium channels. Furthermore, we found these channels also in the wild-type zona glomerulosa where they can partially compensate for an acute inhibition of CaV3.2. Inhibition of both, T- and L-type calcium channels abolished the increase of intracellular calcium caused by angiotensin II. Our study demonstrates that T-type calcium channels are not required to maintain glomerulosa calcium oscillations and aldosterone production.

No abstract

No abstract