Well I don't think pathological protein aggregation is anything to do with CSF pH. The CSF is not bathing the individual cells. CSF surrounds the brain and performs various functions. Within the mass of the organ the gaps between cells are filled with interstitial fluid. These are not the same.

Edit: there are protein aggregation diseases that are systemic and rather horrible. These are bundled together under the term amyloidosis. These do not involve the "amyloid" protein involved in alzheimers disease, rather a diverse range of proteins that aggregate for various reasons. The alzheimers amyloid protein was lumped into this historically. This was because it was recognised that protein clumping was a common feature as amyloid plaques were easily visible histologicaly because they show birefringence under Congo red staining.

These are different diseases from alzheimers but bear in mind that most neuro degenerative diseases involve some form of abnormal protein aggregation, from alpha synuclein in parkinsons to the poly-CAG-opathies such as Huntington disease.

Urine pH can vary pretty wildly. Usually 6 to 7 but I've seen as high as 9 and as low as 5. I'm only measuring it for the purpose of sample preservation prior to other analysis but it is available in our lab as a diagnostic measure, usually related to stone formation. Blood pH also varies as others have said due to respiratory and metabolic issues.