TDP-43 Cryptic RNAs in Perry Syndrome: Differences across Brain Regions and TDP-43 Proteinopathies

Background: Perry syndrome (PS) is a rare and fatal hereditary autosomal dominant neurodegenerative disorder caused by mutations in dynactin (DCTN1). PS brains accumulate inclusions positive for ubiquitin, transactive-response DNA-binding protein of 43 kDa (TDP-43), and to a lesser extent dynactin. Objectives: Little is known regarding the contributions of TDP-43, an RNA binding protein that represses cryptic exon inclusion, in PS. Therefore, we sought to identify the degree of TDP-43 dysfunction in two regions of PS brains. Methods: We evaluated the levels of insoluble pTDP-43 and TDP-43-regulated cryptic RNAs and protein in the caudate nucleus and substantia nigra of 7 PS cases, 12 cases of frontotemporal lobar degeneration (FTLD) with TDP-43 pathology, and 11 cognitively healthy controls without TDP-43 pathology. Results: Insoluble pTDP-43 protein levels were detected in PS brains to a similar extent in the caudate nucleus and substantia nigra but lower than those in FTLD brains. The caudate nucleus of PS showed accumulation of eight TDP-43-regulated cryptic RNAs (ACTL6B, CAMK2B, STMN2, UNC13A, KCNQ2, ATG4B, GPSM2, and HDGFL2) and cryptic protein (HDGFL2) characteristic of FTLD. Conversely, only one cryptic target, UNC13A, reached significance in the substantia nigra despite similar pTDP-43 levels. Conclusion: We detected TDP-43 cryptic RNAs and protein in PS caudate nucleus. Given the importance of cryptic exon biology in the development of biomarkers, and the identification of novel targets for therapeutic intervention, it is imperative we understand the consequences of TDP-43 dysfunction across different brain regions and determine the targets that are specific and common to TDP-43 proteinopathies.