No habituation trial was performed

No habituation trial was performed. by activating cyclin dependent kinase-5. Salt-induced cognitive impairment is not observed in tau-null mice or in mice treated with anti-tau antibodies, despite prolonged cerebral hypoperfusion and neurovascular dysfunction. These findings unveil a causal link between dietary salt, endothelial dysfunction and tau pathology, impartial of hemodynamic insufficiency. Avoiding excessive salt intake and maintaining vascular health may help stave off vascular and neurodegenerative pathologies underlying late-life dementia. Vascular risk factors including excessive salt consumption have long been associated with cerebrovascular diseases and cognitive impairment13. A diet rich in salt is an impartial risk factor for stroke and dementia3,810and has been Kevetrin HCl linked to the cerebral small vessel disease underlying vascular cognitive impairment11, a Rabbit polyclonal to EGFLAM condition associated with endothelial dysfunction and reduced cerebral blood (CBF)12. In mice, a high salt diet (HSD) induces cognitive dysfunction by targeting the cerebral microvasculature through a gut-initiated adaptive immune response mediated by Th17 lymphocytes7. The producing increase in circulating IL17 prospects to inhibition of endothelial nitric oxide (NO) synthase (eNOS) and reduced vascular NO production, which, in turn, impairs endothelial vasoactivity and lowers cerebral blood flow (CBF) by 25%7. However, it remains unclear how hypoperfusion, in HSD or other vascular risk factors, prospects to impaired cognition. The prevailing Kevetrin HCl view is usually that hypoperfusion compromises the delivery of oxygen and glucose to energy-demanding brain regions Kevetrin HCl involved in cognition12,13. But the relatively small CBF reduction associated with HSD in mice7and vascular cognitive impairment in humans14may not be sufficient to impair cognitive function15, implicating vascular factors beyond cerebral perfusion. Excessive phosphorylation of the microtubule associated protein tau promotes the formation of insoluble tau aggregates, thought to mediate neuronal dysfunction and cognitive impairment in AD and other tauopathies16. However, tau accumulation has progressively been detected also in cerebrovascular pathologies associated with endothelial dysfunction and cognitive impairment5,6. Therefore, we investigated whether tau accumulation rather than cerebral hypoperfusion contributes to the cognitive dysfunction induced by HSD. First, we established if HSD induces tau phosphorylation. Male C56Bl/6 mice were placed on a normal diet (ND) or HSD (4 or 8% NaCl), a commonly used model of excessive dietary salt corresponding to a 816 fold increase in the salt content in the regular mouse chow7,17. Phosphorylation of tau epitopes promoting tau aggregation and neuronal dysfunction16were assessed over time by Western blotting. HSD (8%) induced a sustained increase in p-tau (AT8, RZ3) in neocortex and hippocampus without increasing total tau (Tau 46) (Fig. 1a). In the hippocampus, an increase in PHF13 and pSer199Ser202was also observed (Extended Data Fig. 1a). The tau phosphorylation (AT8) was abolished by lambda protein phosphatase (Extended Data Fig. 1b). AT8 and RZ3 were also increased in neocortex of female mice fed a HSD (Extended Data Fig. 1c). HSD did not increase tau acetylation (K280), a post translational modification implicated in tau pathology18(Extended Data Fig. 1a). AT8 and MC1 immunoreactivities were detected in the pyriform cortex, but neurofibrillary tangles were not observed (Fig. 1b,Extended Data Fig. 1d,e). No neuronal or white matter damage was observed, nor significant changes in astrocytes, microglia/macrophages, or pericytes (Extended Data Fig. 2ac). Increased AT8 was also observed in neocortex with lower amounts of dietary salt (4%) (Extended Data Fig. 1f). == Fig. 1: HSD increases tau phosphorylation and insoluble tau. == a,HSD increases AT8 and RZ3 levels. (CTX: AT8, ND/HSD n=8/9, *p<0.0001 vs ND; RZ3, ND/HSD n=12/11, *p<0.0001 vs ND; HIPP: AT8, ND/HSD n=9/9, *p<0.0001 vs ND; RZ3, ND/HSD n=9/9, *p=0.0011 vs ND, two-tailed unpaired t-test).b,HSD increases neuronal AT8 immunoreactivity in the piriform cortex (size bar=500 m; 100 m in inset). Representative images from ND and HSD mice (n=5/group).c,Time course of the neocortical increase in AT8 and RZ3 (AT8, 4 weeks: ND/HSD n=4/5, *p=0.0116 vs ND; 8 weeks: ND/HSD n=9/8, *p=0.0066 vs ND; 24 weeks: ND/HSD n=8/9, *p=0.0152 vs ND; 36 weeks: ND/HSD n=4/5, *p=0.0087.