Biology subjects

Howland, D.

Publications and source records attributed to Howland, D..

7 recordsLinked to original sources

bioRxiv2026

C57BL/6 BAC-CAG Huntingtons disease mice show somatic CAG expansion and responses to small interfering RNAs comparable to the FVB strain

Huntingtons disease (HD) is a neurodegenerative disorder caused by CAG repeat expansion in the huntingtin (HTT) gene, with longer repeats linked to earlier onset. Somatic CAG expansion, particularly in the striatum, contributes to disease progression and is influenced by HTT biology and genetic modifiers. Modulating somatic expansion is emerging as a promising approach to slow or prevent HD, and mouse models have been crucial for preclinical testing of different therapeutic strategies. The BAC-CAG model, developed on the FVB strain, has been used to study somatic expansion of human expanded HTT. However, comparisons with other key HD mouse models have been limited by differences in genetic background, as many other models are on the C57BL/6 strain. The BAC-CAG model has now been developed on a C57BL/6 background. To determine whether the C57BL/6 BAC-CAG model can be used to study and modulate somatic expansion, we compared CAG expansion in mice on C57BL/6 or FVB backgrounds, with and without intraventricular divalent small interfering RNAs (siRNA) targeting HD modifiers MutS homolog 3 (MSH3) and HTT. Both strains exhibited robust, comparable somatic expansion over two months, which was blocked by MSH3-, but not HTT-, targeted siRNA. RNA sequencing identified gene expression differences primarily in pseudogenes, with no differences in endogenous Htt, human HTT, or mismatch repair genes. These results demonstrate that BAC-CAG mice on a C57BL/6 background exhibit somatic CAG expansion comparable to the validated FVB strain, providing a model to study and preclinically test therapies targeting somatic expansion in HD.

neuroscience↗

bioRxiv2025

Blocking somatic repeat expansion and lowering huntingtin via RNA interference synergize to prevent Huntingtons disease pathogenesis in mice

Huntingtons disease (HD) is a progressive neurodegenerative disorder with no approved therapies. Two major molecular drivers--somatic expansion of inherited CAG repeats and toxic mutant HTT (mHTT) variants--lead to neuronal dysfunction. Despite multiple trials, HTT-lowering strategies have not shown meaningful clinical benefit. Using therapeutic divalent siRNAs, we assessed the long-term impact of silencing MSH3 (a key regulator of somatic expansion), HTT, or both. In Q111 HD mice (>110 CAGs), which exhibit robust expansion, mHTT inclusions, and transcriptional dysregulation by 12 months, long-term MSH3 silencing blocked expansion, reduced inclusions, and reversed gene expression changes. HTT silencing alone had limited effect, but combined MSH3/HTT targeting synergistically eliminated inclusions and restored transcriptomic profiles. Parallel treatment in wild-type mice showed no toxicity, supporting the safety of long-term intervention. These findings position somatic expansion as a promising therapeutic target and demonstrate the potential of RNAi-based co-silencing of MSH3 and HTT as a disease-modifying strategy for HD.

neuroscience↗

bioRxiv2024

Suppression of Huntington's Disease Somatic Instability by Transcriptional Repression and Direct CAG Repeat Binding

Huntingtons disease (HD) arises from a CAG expansion in the huntingtin (HTT) gene beyond a critical threshold. A major thrust of current HD therapeutic development is lowering levels of mutant HTT mRNA (mHTT) and protein (mHTT) with the aim of reducing the toxicity of these product(s). Human genetic data also support a key role for somatic instability (SI) in HTTs CAG repeat - whereby it lengthens with age in specific somatic cell types - as a key driver of age of motor dysfunction onset. Thus, an attractive HD therapy would address both mHTT toxicity and SI, but to date the relationship between SI and HTT lowering remains unexplored. Here, we investigated multiple therapeutically-relevant HTT-lowering modalities to establish the relationship between HTT lowering and SI in HD knock-in mice. We find that repressing transcription of mutant Htt (mHtt) provides robust protection from SI, using diverse genetic and pharmacological approaches (antisense oligonucleotides, CRISPR-Cas9 genome editing, the Lac repressor, and virally delivered zinc finger transcriptional repressor proteins, ZFPs). However, we find that small interfering RNA (siRNA), a potent HTT-lowering treatment, lowers HTT levels without influencing SI and that SI is also normal in mice lacking 50% of total HTT levels, suggesting HTT levels, per se, do not modulate SI in trans. Remarkably, modified ZFPs that bind the mHtt locus, but lack a repressive domain, robustly protect from SI, despite not reducing HTT mRNA or protein levels. These results have important therapeutic implications in HD, as they suggest that DNA-targeted HTT-lowering treatments may have significant advantages compared to other HTT-lowering approaches, and that interaction of a DNA-binding protein and HTTs CAG repeats may provide protection from SI while sparing HTT expression.

neuroscience↗

bioRxiv2024

Global Huntingtin Knockout in Adult Mice Leads to Fatal Neurodegeneration that Spares the Pancreas

Huntingtons disease (HD) is a fatal neurogenerative disorder caused by an expanded glutamine-coding CAG tract in the Huntingtin (Htt) gene. HD is believed to primarily arise via a toxic gain of function, and as a result a wide range of Htt-lowering treatments are in clinical trials. The safety of these trials is contingent on the risks imposed by Htt lowering: Htt is widely conserved, ubiquitously expressed and its complete loss causes severe developmental symptoms in mice and humans. Recently, multiple labs have reported on the consequences of widespread inducible Htt loss in mice. One report describes that early induction of global Htt loss causes fatal pancreatitis, but that later onset lowering is benign. Another study did not report fatal pancreatitis but suggested that postnatal Htt loss was associated with widespread progressive phenotypes, including subcortical calcification and neurodegeneration. To better understand the risks posed by widespread inducible Htt loss we established the phenotypes of mice in which we knocked out Htt with two tamoxifen inducible Cre lines, which we have here extensively characterized. In short, we find that widespread loss of Htt at 2 months of age leads to a wide range of phenotypes, including subcortical calcification, but does not result in acute pancreatitis or histological changes in the pancreas. Additionally, we report here for the first time that Htt loss is followed by robust and sustained increases in the levels of neurofilament light chain (NfL), a peripherally accessible biomarker of neuroaxonal stress. These results confirm that complete loss of Htt in mice is associated with pronounced risks, including progressive subcortical calcification and neurodegeneration.

neuroscience↗

bioRxiv2023

Huntingtin loss in hepatocytes is associated with altered metabolism, adhesion, and liver zonation

Huntingtons disease arises from a toxic gain of function in the huntingtin (HTT) gene. As a result, many HTT-lowering therapies are being pursued in clinical studies, including those that reduce HTT RNA and protein expression in the liver. To investigate potential impacts, we characterized molecular, cellular, and metabolic impacts of chronic HTT lowering in mouse hepatocytes. Lifelong hepatocyte HTT loss is associated with multiple physiological changes, including increased circulating bile acids, cholesterol and urea, hypoglycemia, and impaired adhesion. HTT loss causes a clear shift in the normal zonal patterns of liver gene expression, such that pericentral gene expression is reduced. These alterations in liver zonation in livers lacking HTT are observed at the transcriptional, histological and plasma metabolite level. We have extended these phenotypes physiologically with a metabolic challenge of acetaminophen, for which the HTT loss results in toxicity resistance. Our data reveal an unexpected role for HTT in regulating hepatic zonation, and we find that loss of HTT in hepatocytes mimics the phenotypes caused by impaired hepatic {beta}-catenin function. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=89 SRC="FIGDIR/small/546334v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1dd0f15org.highwire.dtl.DTLVardef@938f7org.highwire.dtl.DTLVardef@17ae025org.highwire.dtl.DTLVardef@11cd15_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2022

Benefits of global mutant huntingtin lowering diminish over time in a Huntington's disease mouse model

We have developed a novel inducible Huntingtons disease (HD) mouse model that allows temporal control of whole-body allele-specific mutant Huntingtin (mHtt) expression. We asked whether moderate global lowering of mHtt ([~]50%) was sufficient for long-term amelioration of HD-related deficits and, if so, whether early mHtt lowering (before measurable deficits) was required. Both early and late mHtt lowering delayed behavioral dysfunction and mHTT protein aggregation, as measured biochemically. However, long-term follow up revealed that the benefits, in all mHtt lowering groups, attenuated by 12 months of age. While early mHtt lowering attenuated cortical and striatal transcriptional dysregulation evaluated at 6 months of age, the benefits diminished by 12- months of age and late mHtt lowering was unable to ameliorate striatal transcriptional dysregulation at 12 months of age. Only early mHtt lowering delayed the elevation in cerebrospinal fluid neurofilament light chain that we observed in our model starting at 9 months of age. As small-molecule HTT-lowering therapeutics progress to the clinic, our findings suggest that moderate mHtt lowering allows disease progression to continue, albeit at a slower rate, and could be relevant to the degree of mHTT lowering required to sustain long-term benefit in humans.

neuroscience↗

bioRxiv2018

A three dimensional multiplane kinematic model for bilateral hind limb gait analysis in cats

Background: Kinematic gait analysis is an important noninvasive technique used for quantitative evaluation and description of locomotion and other movements in healthy and injured populations. Three dimensional (3D) kinematic analysis offers additional outcome measures including internal-external rotation not characterized using sagittal plane analysis techniques.\n\nMethods: The objectives of this study were to 1) develop and evaluate a 3D hind limb multiplane kinematic model for gait analysis in cats using joint coordinate systems, 2) implement and compare two 3D stifle (knee) prediction techniques, and 3) compare flexion-extension determined using the multiplane model to a sagittal plane model. Walking gait was recorded in 3 female adult cats (age = 2.9 years, weight = 3.5 {+/-} 0.2 kg). Kinematic outcomes included flexion-extension, internal-external rotation, and abduction-adduction of the hip, stifle, and tarsal (ankle) joints.\n\nResults: Each multiplane stifle prediction technique yielded similar findings. Joint angles determined using markers placed on skin above bony landmarks in vivo were similar to joint angles determined using a feline hind limb skeleton in which markers were placed directly on landmarks ex vivo. Differences in hip, stifle, and tarsal joint flexion-extension were demonstrated when comparing the multiplane model to the sagittal plane model.\n\nConclusions: This multiplane cat kinematic model can predict joint rotational kinematics as a tool that can quantify frontal, transverse, and sagittal plane motion. This model has multiple advantages given its ability to characterize joint internal-external rotation and abduction-adduction. A further, important benefit is greater accuracy in representing joint flexion-extension movements.

neuroscience↗