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R2710 --> 717.2 --> Alzheimer's Disease (AD) is an emerging global health care crisis. However, underlying mechanisms are not understood well enough to translate to precision medicine. There is increasing evidence suggesting that AD is associated with brain hypoperfusion. However, it is unclear whether amyloid‐beta (Aβ) accumulation is a cause or consequence of AD, and how it contributes to cerebral hypoperfusion. The present study examined if Aβ accumulation induces cerebral hypoperfusion in AD by affecting cerebral vascular function via both anterograde (arteriole‐to‐capillary) and retrograde (capillary‐to‐arteriole) pathways in the TgF344‐AD rat model of Alzheimer's disease. We first confirmed that AD rats displayed hippocampal‐based cognitive dysfunction at 6 months of age using an eight‐arm water maze. We then found that AD rats exhibited impaired myogenic response (MR) of middle cerebral arteries (MCAs) and penetrating and parenchymal arterioles (PAs) two months earlier than the onset of cognitive deficits using a Living System pressure myograph. AD rats displayed poor surface and deep cortical cerebral blood flow (CBF) autoregulation recorded by laser Doppler flowmetry, and reduced functional hyperemic response induced by whisker stimulation. Moreover, cell contractile capabilities, detected by collagen gel based‐cell contraction kit, were reduced in Aβ‐treated cerebral VSMCs isolated from F344 rats, similar as seen in VSMCs isolated from AD rats. Furthermore, we found that the productions of reactive oxygen species (ROS) and mitochondrial superoxide in cerebral VSMCs isolated from AD rats were elevated using DHE staining and MitoSOX staining. Moreover, AD cells exhibited reduced mitochondrial respiration and ATP production detected by the Seahorse Cell Mito Stress Test kit. AD cerebral VSMCs also exhibited disrupted actin cytoskeleton and contractile units utilizing immunohistochemistry. Oxidative stress, mitochondrial dysfunction, and actin cytoskeleton disorganization are all factors that are associated with the reduced contractile capabilities of cerebral VSMCs mediated MR and CBF autoregulation. In other studies, we found that capillary endothelial cell‐derived inward rectifier potassium (Kir2.1) activity, which is responsible for retrograde CBF regulation, was reduced in the brain of AD rats using Western blot. PAs with capillaries isolated from AD rats dilated to a lesser degree than WT rats in response to moderately elevated extracellular K+ (10 mM) applied to capillaries. Inhibition of Kir2.1 channels with ML133 diminished the vasodilatory response to a greater extent in WT rats. These findings indicate that Aβ accumulation is associated with cerebral hypoperfusion in AD by affecting cerebral vascular function via both anterograde and retrograde pathways and provide novel insight into the vascular contribution to AD. [ABSTRACT FROM AUTHOR]

R1943 --> We recently reported that cerebral vascular dysfunction precedes cognitive impairment in TgF344‐AD (AD) rat model of Alzheimer's disease. However, whether abnormalities in cerebral vascular smooth muscle cells (VSMCs) play a direct role has not been studied. In the present study, we first confirmed that the AD rats started to develop learning and memory deficits at 24‐week of age using an eight‐arm water maze. AD rats (n = 11) took a longer time to escape and displayed more errors than age‐matched wildtype (WT) rats (n = 6). We also completed a longitudinal comparison of the myogenic response (MR) of the middle cerebral artery (MCA) and found that the MR was similar in AD and WT rats at 8‐ to 12‐week of age when perfusion pressure was increased from 40 to 180 mmHg. However, the MR started first became significantly reduced in 16‐week old AD rats (n = 6) as the inner diameter of the MCA only decreased by 8.2 ± 2.4% when perfusion pressure was increased from 40 to 180 mmHg compared with 14.5% ± 2.0% in age‐matched WT rats (n = 6). The impaired MR of the MCA was exacerbated in AD rats with aging. Consistent with the exvivo MR studies, in vivo experiment using a laser‐Doppler flowmeter demonstrated that the cerebral blood flow (CBF) autoregulation of AD rats (n = 4) was impaired in the surface and deep cortex at 24‐week of age compared to age‐matched WT rats (n = 4). Furthermore, we found an endogenous reduced cell contractile capability in the cerebral VSMCs isolated from AD (n = 4) compared with WT rats (n = 4), detected by a maximal gel size reduction by 15.7 ± 0.9% vs. 25.4 ± 1.0% using a collagen gel‐based assay kit. These results provide evidence that cerebral VSMC dysfunction, impaired MR and autoregulation of CBF correlates, which precedes the development of memory and learning deficits in the TgF344‐AD rats. However, the underlying mechanisms causing the loss of VSMCs contractility in this AD model expressing mutant human amyloid precursor protein (APPsw) and presenilin 1 (PS1ΔE9) genes remains to be determined. Nevertheless, these results provide novel insight into vascular contribution to AD, which will lay the foundation for the discovery of new biomarkers in AD. [ABSTRACT FROM AUTHOR]

R1636 --> 20‐HETE is a metabolite of arachidonic acid produced by enzymes of CYP4A and CYP4F families. We previously reported that Dahl S rats have a genetic deficiency in the production of 20‐HETE and the expression of CYP4A enzymes and exhibit impaired myogenic response of the middle cerebral artery (MCA) and autoregulation of cerebral blood flow (CBF) but the mechanism is unknown. The present study explored whether 20‐HETE has direct effects on the regulation of cerebral mural cell contractility that may play an essential role in autoregulation of CBF in the surface and deep cortex. We found that CYP4A was expressed in vascular smooth muscle cells (VSMCs) and pericytes along parenchymal arteries and capillaries isolated from the MCA territory of SD rats. Gel size was reduced to a lesser extent in VSMCs treated with the 20‐HETE synthesis inhibitor, HET0016 (10 μM) versus vehicle (17.9 ± 0.5 % vs. 28.3 ± 0.5 %; n = 9), indicating loss of contractility. Similarly, constriction of cerebral pericytes treated with HET0016 was reduced relative to controls. Cell contractile capability of cerebral VSMC and pericyte collaboratively play a role in regulating CBF in the superficial and deep cortex of the brain by modulation of the myogenic response of the MCA and arterioles, respectively. CBF was well autoregulated in the surface and deep cortex in SD rats and only increased by 12.9 ± 1.7 % and 13.3 ± 1.9 %, respectively, when pressure was elevated from 100 to 140 mmHg. In contrast, CBF increased by 34.6 ± 3.2 % and 28.5 ± 2.3 %, respectively after the rats were given HET0016 (2 mg/kg). These results demonstrate that CYP4A is expressed both in VSMC and pericytes of parenchymal arteries and capillaries, that blockade of 20‐HETE reduces the contractile activity of these cells and attenuates autoregulation of CBF in the superficial and deep cortex of the brain. They provide novel insight into human genetic studies indicating that inactivate variants of 20‐HETE producing enzymes are associated with a higher incidence of hypertension, stroke, and AD. [ABSTRACT FROM AUTHOR]