Cognitive impairment appears progressive in the mdx mouse

Memory impairment in the D2.mdx mouse model of Duchenne muscular dystrophy is prevented by the adiponectin receptor agonist ALY688

NEW FINDINGS

What is the central question of this study? Can adiponectin receptor agonism improve recognition memory in a mouse model of Duchenne muscular dystrophy? What is the main finding and its importance? Short-term treatment with the new adiponectin receptor agonist ALY688 improves recognition memory in D2.mdx mice. This finding suggests that further investigation into adiponectin receptor agonism is warranted, given that there remains an unmet need for clinical approaches to treat this cognitive dysfunction in people with Duchenne muscular dystrophy.

ABSTRACT

Memory impairments have been well documented in people with Duchenne muscular dystrophy (DMD). However, the underlying mechanisms are poorly understood, and there is an unmet need to develop new therapies to treat this condition. Using a novel object recognition test, we show that recognition memory impairments in D2.mdx mice are completely prevented by daily treatment with the new adiponectin receptor agonist ALY688 from day 7 to 28 of age. In comparison to age-matched wild-type mice, untreated D2.mdx mice demonstrated lower hippocampal mitochondrial respiration (carbohydrate substrate), greater serum interleukin-6 cytokine content and greater hippocampal total tau and Raptor protein contents. Each of these measures was partly or fully preserved after treatment with ALY688. Collectively, these results indicate that adiponectin receptor agonism improves recognition memory in young D2.mdx mice.

Clinical study on cognitive impairment in Duchenne muscular dystrophy

Our study aimed to explore the intellectual function of patients with Duchenne muscular dystrophy (DMD) in China and examine the correlation of full-scale intelligence quotient (FSIQ) with age, mutation locations, mutation class, and dystrophin isoforms. We assessed 64 boys with DMD using The Wechsler Intelligence Scales for Children-Fourth Edition and compared intellectual function at enrollment and follow-up in the 15 patients who completed the follow-up. Our findings confirm that boys with DMD may exhibit cognitive impairment, with the Working Memory Index being the most impaired. There was no significant correlation between FSIQ and age; however, a positive correlation was noted between age and the Verbal Comprehension Index. FSIQ was not associated with mutation class, the number of affected mutated exons, or mutation locations. However, there was a significant difference in FSIQ between the groups with intact and deficient Dp140. Fifteen participants adhered to glucocorticoid therapy throughout the two-year follow-up period, and eleven of them showed an improvement in FSIQ compared to their initial scores, with improvement ranging from 2 to 20. In conclusion, patients with the cumulative loss of isoforms in the brain are at a higher risk of cognitive deficits and may require early cognitive interventions.

APP in the Neuromuscular Junction for the Development of Sarcopenia and Alzheimer's Disease

Sarcopenia, an illness condition usually characterized by a loss of skeletal muscle mass and muscle strength or function, is often associated with neurodegenerative diseases, such as Alzheimer's disease (AD), a common type of dementia, leading to memory loss and other cognitive impairment. However, the underlying mechanisms for their associations and relationships are less well understood. The App, a Mendelian gene for early-onset AD, encodes amyloid precursor protein (APP), a transmembrane protein enriched at both the neuromuscular junction (NMJ) and synapses in the central nervous system (CNS). Here, in this review, we highlight APP and its family members' physiological functions and Swedish mutant APP (APP_swe)'s pathological roles in muscles and NMJ. Understanding APP's pathophysiological functions in muscles and NMJ is likely to uncover insights not only into neuromuscular diseases but also AD. We summarize key findings from the burgeoning literature, which may open new avenues to investigate the link between muscle cells and brain cells in the development and progression of AD and sarcopenia.

A Protocol for Simultaneous In Vivo Imaging of Cardiac and Neuroinflammation in Dystrophin-Deficient MDX Mice Using [18F]FEPPA PET

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder caused by dystrophin loss-notably within muscles and the central neurons system. DMD presents as cognitive weakness, progressive skeletal and cardiac muscle degeneration until pre-mature death from cardiac or respiratory failure. Innovative therapies have improved life expectancy; however, this is accompanied by increased late-onset heart failure and emergent cognitive degeneration. Thus, better assessment of dystrophic heart and brain pathophysiology is needed. Chronic inflammation is strongly associated with skeletal and cardiac muscle degeneration; however, neuroinflammation's role is largely unknown in DMD despite being prevalent in other neurodegenerative diseases. Here, we present an inflammatory marker translocator protein (TSPO) positron emission tomography (PET) protocol for in vivo concomitant assessment of immune cell response in hearts and brains of a dystrophin-deficient mouse model [mdx:utrn(+/-)]. Preliminary analysis of whole-body PET imaging using the TSPO radiotracer, [¹⁸F]FEPPA in four mdx:utrn(+/-) and six wildtype mice are presented with ex vivo TSPO-immunofluorescence tissue staining. The mdx:utrn(+/-) mice showed significant elevations in heart and brain [¹⁸F]FEPPA activity, which correlated with increased ex vivo fluorescence intensity, highlighting the potential of TSPO-PET to simultaneously assess presence of cardiac and neuroinflammation in dystrophic heart and brain, as well as in several organs within a DMD model.

The unconditioned fear response in dystrophin-deficient mice is associated with adrenal and vascular function

Loss of function mutations in the gene encoding dystrophin elicits a hypersensitive fear response in mice and humans. In the dystrophin-deficient mdx mouse, this behaviour is partially protected by oestrogen, but the mechanistic basis for this protection is unknown. Here, we show that female mdx mice remain normotensive during restraint stress compared to a hypotensive and hypertensive response in male mdx and male/female wildtype mice, respectively. Partial dystrophin expression in female mdx mice (heterozygous) also elicited a hypertensive response. Ovariectomized (OVX) female mdx mice were used to explain the normotensive response to stress. OVX lowered skeletal muscle mass and lowered the adrenal mass and zona glomerulosa area (aldosterone synthesis) in female mdx mice. During a restraint stress, OVX dampened aldosterone synthesis and lowered the corticosterone:11-dehydrocorticosterone. All OVX-induced changes were restored with replacement of oestradiol, except that oestradiol lowered the zona fasciculata area of the adrenal gland, dampened corticosterone synthesis but increased cortisol synthesis. These data suggest that oestrogen partially attenuates the unconditioned fear response in mdx mice via adrenal and vascular function. It also suggests that partial dystrophin restoration in a dystrophin-deficient vertebrate is an effective approach to develop an appropriate hypertensive response to stress.

Inhibition of hippocampal cyclin-dependent kinase 5 activity ameliorates learning and memory dysfunction in a mouse model of bronchopulmonary dysplasia

AIMS

Oxygen therapy plays a vital role in the development of bronchopulmonary dysplasia (BPD), which is the independent risk factor for neurodevelopment deficits in premature infants. However, the effect of hippocampal cyclin-dependent kinase 5 (CDK5) on BPD-associated neurodevelopment deficits is not fully understood.

METHODS

Mice were placed in a hyperoxia chamber from postnatal Day 1 to Day 7. Hematoxylin and eosin staining was used to evaluate the lung histomorphological characteristics. Learning and memory functions of mice were detected by Morris water maze. TUNEL staining was applied to measure the number of apoptotic cells. The expression of CDK5, apoptosis-related protein, and neuroplasticity-related proteins were analyzed by Western blot. Golgi staining was used to assess the structure of dendritic spines.

RESULTS

Hyperoxia-induced BPD mice showed a long-term learning and memory dysfunction, more severe neuronal apoptosis, and a decline of synaptic plasticity. Inhibition of CDK5 overactivation ameliorated cognitive deficits, neuronal apoptosis, and synaptic plasticity disorders in BPD mice.

CONCLUSIONS

This study first found a vital role of CDK5 in BPD-associated neurodevelopmental disorders. Inhibition of CDK5 overexpression could effectively improve cognitive dysfunctions in BPD mice, which indicated that hippocampal CDK5 may be a new target for prevention and treatment in learning and memory dysfunction of BPD.

Wechsler Scale Intelligence Testing in Males with Dystrophinopathies: A Review and Meta-Analysis

BACKGROUND

Intelligence scores in males with Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD) remain a major issue in clinical practice. We performed a literature review and meta-analysis to further delineate the intellectual functioning of dystrophinopathies.

METHOD

Published, peer-reviewed articles assessing intelligence, using Wechsler Scales, of males with DMD or BMD were searched from 1960 to 2022. Meta-analysis with random-effects models was conducted, assessing weighted, mean effect sizes of full-scale IQ (FSIQ) scores relative to normative data (Mean = 100, Standard Deviation = 15). Post hoc we analysed differences between performance and verbal intelligence scores.

RESULTS

43 studies were included, reporting data on 1472 males with dystrophinopathies; with FSIQ scores available for 1234 DMD (k = 32) and 101 BMD (k = 7). DMD males score, on average, one standard deviation below average (FSIQ = 84.76) and significantly lower than BMD (FSIQ = 92.11). Compared to a previous meta-analysis published in 2001, we find, on average, significantly higher FSIQ scores in DMD.

CONCLUSION

Males with Duchenne have, on average, significantly lower FSIQ scores than BMD males and the general population. Clinicians must consider lower intelligence in dystrophinopathies to ensure good clinical practice.

Implications of notch signaling in duchenne muscular dystrophy

This review focuses upon the implications of the Notch signaling pathway in muscular dystrophies, particularly Duchenne muscular dystrophy (DMD): a pervasive and catastrophic condition concerned with skeletal muscle degeneration. Prior work has defined the pathogenesis of DMD, and several therapeutic approaches have been undertaken in order to regenerate skeletal muscle tissue and ameliorate the phenotype. There is presently no cure for DMD, but a promising avenue for novel therapies is inducing muscle regeneration via satellite cells (muscle stem cells). One specific target using this approach is the Notch signaling pathway. The canonical Notch signaling pathway has been well-characterized and it ultimately governs cell fate decision, cell proliferation, and induction of differentiation. Additionally, inhibition of the Notch signaling pathway has been directly implicated in the deficits seen with muscular dystrophies. Here, we explore the connection between the Notch signaling pathway and DMD, as well as how Notch signaling may be targeted to improve the muscle degeneration seen in muscular dystrophies.

α-Dystrobrevin knockout mice have increased motivation for appetitive reward and altered brain cannabinoid receptor 1 expression

α-Dystrobrevin (α-DB) is a major component of the dystrophin-associated protein complex (DAPC). Knockout (KO) of α-DB in the brain is associated with astrocytic abnormalities and loss of neuronal GABA receptor clustering. Mutations in DAPC proteins are associated with altered dopamine signaling and cognitive and psychiatric disorders, including schizophrenia. This study tested the hypothesis that motivation and associated underlying biological pathways are altered in the absence of α-DB expression. Male wildtype and α-DB KO mice were tested for measures of motivation, executive function and extinction in the rodent touchscreen apparatus. Subsequently, brain tissues were evaluated for mRNA and/or protein levels of dysbindin-1, dopamine transporter and receptor 1 and 2, mu opioid receptor 1 (mOR1) and cannabinoid receptor 1 (CB1). α-DB KO mice had significantly increased motivation for the appetitive reward, while measures of executive function and extinction were unaffected. No differences were observed between wildtype and KO animals on mRNA levels of dysbindin-1 or any of the dopamine markers. mRNA levels of mOR1were significantly decreased in the caudate-putamen and nucleus accumbens of α-DB KO compared to WT animals, but protein levels were unaltered. However, CB1 protein levels were significantly increased in the prefrontal cortex and decreased in the nucleus accumbens of α-DB KO mice. Triple-labelling immunohistochemistry confirmed that changes in CB1 were not specific to astrocytes. These results highlight a novel role for α-DB in the regulation of appetitive motivation that may have implications for other behaviours that involve the dopaminergic and endocannabinoid systems.

Kynurenine metabolism is altered in mdx mice: A potential muscle to brain connection

NEW FINDINGS

Research has shown that promoting muscle health with regular aerobic exercise can improve mental health through a kynurenine metabolic pathway. With regular aerobic exercise, kynurenine metabolism is favourably altered towards a neuroprotective pathway that promotes kynurenic acid production through increased expression of PGC-1α, kynurenine amino acid transferase (KAT) enzymes, and lowered inflammation. Whether conditions of muscle disease such as muscular dystrophy can negatively influence this pathway remains unknown. We show that the DBA/2J mdx model of Duchenne muscular dystrophy exhibit altered kynurenine metabolism with less KYNA and PGC-1α and the highest level of TNF-a mRNA - results associated with anxiety-like behaviour.

ABSTRACT

Regular exercise can direct muscle kynurenine (KYN) metabolism toward the neuroprotective branch of the kynurenine pathway thereby limiting the accumulation of neurotoxic metabolites in the brain and contributing to mental resilience. However, the effect of muscle disease on KYN metabolism has not yet been investigated. Previous work has highlighted anxiety-like behaviors in approximately 25% of patients with Duchenne muscular dystrophy (DMD), possibly due to altered KYN metabolism. Here, we characterized KYN metabolism in mdx mouse models of DMD. Young (8-10 week old) DBA/2J (D2) mdx mice, but not age-matched C57BL/10 (C57) mdx mice, had lower levels of circulating KYNA and KYNA:KYN ratio compared with their respective wild-type (WT) controls. While both C57 and D2 mdx mice displayed signs of anxiety-like behaviour, spending more time in the corners of the arena during a novel object recognition test, this effect was more prominent in D2 mdx mice. Correlational analysis detected a significant negative association between KYNA:KYN levels and time spent in corners in D2 mice, but not C57 mice. In extensor digitorum longus muscles from D2 mdx mice, but not C57 mdx mice, we found lowered protein levels of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha and kynurenine amino transferase-1 enzyme when compared with WT. Furthermore, D2 mdx quadricep muscles had the highest level of TNF-α expression, which is suggestive of enhanced inflammation. Thus, our pilot work shows that KYN metabolism is altered in D2 mdx mice, with a potential contribution from altered muscle health. This article is protected by copyright. All rights reserved.

Dystrophin deficiency affects human astrocyte properties and response to damage

In addition to progressive muscular degeneration due to dystrophin mutations, 1/3 of Duchenne muscular dystrophy (DMD) patients present cognitive deficits. However, there is currently an incomplete understanding about the function of the multiple dystrophin isoforms in human brains. Here, we tested the hypothesis that dystrophin deficiency affects glial function in DMD and could therefore contribute to neural impairment. We investigated human dystrophin isoform expression with development and differentiation and response to damage in human astrocytes from control and induced pluripotent stem cells from DMD patients. In control cells, short dystrophin isoforms were up-regulated with development and their expression levels changed differently upon neuronal and astrocytic differentiation, as well as in 2-dimensional versus 3-dimensional astrocyte cultures. All DMD-astrocytes tested displayed altered morphology, proliferative activity and AQP4 expression. Furthermore, they did not show any morphological change in response to inflammatory stimuli and their number was significantly lower as compared to stimulated healthy astrocytes. Finally, DMD-astrocytes appeared to be more sensitive than controls to oxidative damage as shown by their increased cell death. Behavioral and metabolic defects in DMD-astrocytes were consistent with gene pathway dysregulation shared by lines with different mutations as demonstrated by bulk RNA-seq analysis. Together, our DMD model provides evidence for altered astrocyte function in DMD suggesting that defective astrocyte responses may contribute to neural impairment and might provide additional potential therapeutic targets.

Characterization of Alzheimer's disease-like neuropathology in Duchenne's muscular dystrophy using the DBA/2J mdx mouse model

Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder caused by a mutation in the dystrophin gene. In addition to muscle pathology, some patients with DMD will exhibit cognitive impairments with severity being linked to age and type of genetic mutation. Likewise, some studies have shown that mdx mice display impairments in spatial memory compared with wild‐type (WT) controls, while others have not observed any such effect. Most studies have utilized the traditional C57BL/10 (C57) mdx mouse, which exhibits a mild disease phenotype. Recently, the DBA/2J (D2) mdx mouse has emerged as a more severe and perhaps clinically relevant DMD model; however, studies examining cognitive function in these mice are limited. Thus, in this study we examined cognitive function in age‐matched C57 and D2 mdx mice along with their respective WT controls. Our findings show that 8‐ to 12‐week‐old C57 mdx mice did not display any differences in exploration time when challenged with a novel object recognition test. Conversely, age‐matched D2 mdx mice spent less time exploring objects in total as a well as less time exploring the novel object, suggestive of impaired recognition memory. Biochemical analyses of the D2 mdx brain revealed higher soluble amyloid precursor protein β (APPβ) and APP in the prefrontal cortex of mdx mice compared with WT, and lower soluble APPα in the hippocampus, suggestive of a shift towards amyloidogenesis and a similar pathogenesis to Alzheimer's disease. Furthermore, our study demonstrates the utility of the D2 mdx model in studying cognitive impairment.

Emotional behavior and brain anatomy of the mdx52 mouse model of Duchenne muscular dystrophy

The exon-52-deleted mdx52 mouse is a critical model of Duchenne muscular dystrophy (DMD), as it features a deletion in a hotspot region of the DMD gene, frequently mutated in patients. Deletion of exon 52 impedes expression of several brain dystrophins (Dp427, Dp260 and Dp140), thus providing a key model for studying the cognitive impairment associated with DMD and testing rescuing strategies. Here, using in vivo magnetic resonance imaging and neurohistology, we found no gross brain abnormalities in mdx52 mice, suggesting that the neural dysfunctions in this model are likely at the level of brain cellular functionalities. Then, we investigated emotional behavior and fear learning performance of mdx52 mice compared to mdx mice that only lack Dp427 to focus on behavioral phenotypes that could be used in future comparative preclinical studies. mdx52 mice displayed enhanced anxiety and a severe impairment in learning an amygdala-dependent Pavlovian association. These replicable behavioral outcome measures are reminiscent of the internalizing problems reported in a quarter of DMD patients, and will be useful for preclinical estimation of the efficacy of treatments targeting brain dysfunctions in DMD.

Abnormalities in Brain and Muscle Microstructure and Neurochemistry of the DMD Rat Measured by in vivo Diffusion Tensor Imaging and High Resolution Localized 1H MRS

Duchenne muscular dystrophy (DMD) is an X-linked disorder caused by the lack of dystrophin with progressive degeneration of skeletal muscles. Most studies regarding DMD understandably focus on muscle, but dystrophin is also expressed in the central nervous system, potentially resulting in cognitive and behavioral changes. Animal models are being used for developing more comprehensive neuromonitoring protocols and clinical image acquisition procedures. The recently developed DMD rat is an animal model that parallels the progressive muscle wasting seen in DMD. Here, we studied the brain and temporalis muscle structure and neurochemistry of wild type (WT) and dystrophic (DMD) rats using magnetic resonance imaging and spectroscopy. Both structural and neurochemistry alterations were observed in the DMD rat brain and the temporalis muscle. There was a decrease in absolute brain volume (WT = 1579 mm³; DMD = 1501 mm³; p = 0.039, Cohen’s d = 1.867), but not normalized (WT = 4.27; DMD = 4.02; p = 0.306) brain volume. Diffusion tensor imaging (DTI) revealed structural alterations in the DMD temporalis muscle, with increased mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). In the DMD rat thalamus, DTI revealed an increase in fractional anisotropy (FA) and a decrease in RD. Smaller normalized brain volume correlated to severity of muscle dystrophy (r = −0.975). Neurochemical changes in the DMD rat brain included increased GABA and NAA in the prefrontal cortex, and GABA in the hippocampus. Such findings could indicate disturbed motor and sensory signaling, resulting in a dysfunctional GABAergic neurotransmission, and an unstable osmoregulation in the dystrophin-null brain.