N17 Modifies Mutant Huntingtin Nuclear Pathogenesis and Severity of Disease in HD BAC Transgenic Mice

Abstract

SUMMARYThe nucleus is a critical subcellular compartment for the pathogenesis of polyglutamine disorders, including Huntington’s disease (HD). Recent studies suggest the first 17-amino-acid domain (N17) of mutant Huntingtin (mHTT) mediates its nuclear exclusion in cultured cells. Here, we test whether N17 could be a molecular determinant of nuclear mHTT pathogenesis in vivo. BAC transgenic mice expressing mHTT lacking the N17 domain (BACHD-ΔN17) show dramatically accelerated mHTT pathology exclusively in the nucleus, which is associated with HD-like transcriptionopathy. Interestingly, BACHD-ΔN17 mice manifest more overt disease-like phenotypes than the original BACHD mice, including body weight loss, movement deficits, robust striatal neuronal loss, and neuroinflammation. Mechanistically, N17 is necessary for nuclear exclusion of small mHTT fragments that are part of nuclear pathology in HD. Together, our study suggests that N17 modifies nuclear pathogenesis and disease severity in HD mice by regulating subcellular localization of known nuclear pathogenic mHTT species.

Profilin reduces aggregation and phase separation of huntingtin N-terminal fragments by preferentially binding to soluble monomers and oligomers

“…Recent in vivo studies from Yang and coworkers showed that a ∆N17 variant of huntingtin, which lacks the N17 module, leads to faithful reproduction of HD phenotypes in transgenic mice (56,57). In light of these observations, and given the relative ease of synthesis and purification of Htt-NTFs that lack the N17 module (19), we used constructs of the form Q n -C38 for a majority of our in vitro experiments.…”

Structure/Function Analysis of the Huntingtin N-terminus Encoded by Htt Exon 1 Using Knock-In Mouse Models

“…Far less in vivo data with endogenous Htt expression levels, and with deletion mutations generated in the context of the full-length Htt protein exists. However, BACHD-ΔN17 mice, where the N17 domain has been deleted from the expanded Htt allele, have been generated and characterized [124]. In these mice, deletion of the N17 domain results in accelerated and worsened behavioral and neuropathological phenotypes compared to control BACHD mice, demonstrating that the presence of the N17 domain reduces the toxicity of mHtt [124].…”

“…However, BACHD-ΔN17 mice, where the N17 domain has been deleted from the expanded Htt allele, have been generated and characterized [124]. In these mice, deletion of the N17 domain results in accelerated and worsened behavioral and neuropathological phenotypes compared to control BACHD mice, demonstrating that the presence of the N17 domain reduces the toxicity of mHtt [124]. Ultimately, in vivo methods are needed to confirm the in bold and underlined, the NarI site is underlined).…”

“…To determine if BAC-HD-∆N17 or BAC-WT-∆N17 expression on a Htt-null genetic background was sufficient for normal embryonic development, the BAC transgenic models were crossed with Htt +/-mice, to generate BAC-HD-∆N17-Htt -/-and BAC-WT-∆N17-Htt -/-progeny and control littermates [124].…”

“…-/-mice were born at normal Mendelian frequencies [124]. Therefore, despite the conservation of this domain throughout vertebrate evolution, the N17 domain is not required for embryonic development.…”