Small rnas in cerebrospinal fluid samples from patients with Alzheimer's disease and neurologically normal controls

Abstract

Aside from microRNA, very little is known about other small RNA species that can be detected in cerebrospinal fluid. For example, piwi-interacting RNAs are a highly diverse class of small RNA. They were recently identified to have expression outside of germline cells, and were found to be expressed in the brain. Changes in these other small RNAs have not yet been extensively studied with respect to the pathology associated with Alzheimer's disease. Cell-free RNA was isolated from 1 mL cerebrospinal fluid samples. As proof-of-principal, we sequenced the small RNA content from cerebrospinal fluid samples from patients with Alzheimer's disease, Parkinson's disease and neurologically normal control subjects (>50 subjects in each category). All subjects were postmortem and had full pathology reports. We assessed the small RNA findings with regards to pathology as well as confirmed disease diagnosis. We were able to detect several abundant small RNA species in addition to microRNAs that are consistently expressed in our cerebrospinal fluid samples, including small nucleolar RNAs, small nuclear RNAs and piwi-interacting RNAs. Using piwi-interacting RNAs as an example, we detected 7922 piRNAs across all cerebrospinal fluid samples. A total of 109 piwi-interacting RNAs were consistently detected in more than 90% of the samples, with a mean normalized expression of 549 and maximum of 15460 counts. When we examined piwi-interacting RNA levels between Alzheimer's patients and neurologically normal controls, we found several to be differentially expressed. We also found several differentially expressed piwi-interacting RNA between Alzheimer's and Parkinson's patients. These data demonstrate that, in addition to microRNA, there are other small RNA species that can be detected in cerebrospinal fluid. We identified piwi-interacting RNAs that were differentially expressed in cerebrospinal fluid samples from Alzheimer's disease patients when compared to controls and Parkinson's patients. In comparison with serum samples from the same individuals, there are nearly twice as many detected piwi-interacting RNA in cerebrospinal fluid. These data suggest that there may be additional small RNAs regulating the pathogenesis of Alzheimer's disease and that they are detectable in cerebrospinal fluid.