Spinocerebellar ataxia type 7 (SCA‐7) is a neurodegenerative polyglutamine disease within the family of spinocerebellar ataxias. Classically SCA7 is a disease of ataxia and vision loss. However, patients with SCA also have difficulty breathing, swallowing, coughing and maintaining a stable open airway which often result in fatal respiratory failure. While respiratory measures have been reported in other SCA mouse models, ventilation in a SCA‐7 mouse has not yet been studied. Using the SCA‐7 mouse model (Atxn7 266Q/+ ) we sought to characterize the respiratory pathology of SCA‐7. Whole body plethysmography (WBP) was used to assess respiratory dysfunction in the Atxn7 266Q/+ mouse both at baseline breathing (FiO2: 0.21; nitrogen balance) and during a hypercapnic and hypoxic challenge (Fi:CO2: 0.07, FiO2: 0.10; nitrogen balance). Neurobehavioral testing and strength was assessed using the inverted screen test and the grip strength test. Post mortem histological analysis was performed on the phrenic and hypoglossal motor neurons and nerves. At 4 weeks of age, the SCA‐7 mice are indistinguishable from their unaffected littermates. However, by 8 weeks of age, SCA‐7 mice perform poorly on both neurobehavioral and strength tests as compared to their WT littermates. 50% of the SCA‐7 mice died by 9 weeks, while littermate controls thrived. SCA‐7 mice have elevated respiratory rate at baseline, as well as reduced tidal volume, minute ventilation, peak inspiratory flow, peak expiratory flow, and inspiratory time during the respiratory challenge. These results indicate that the SCA‐7 mice have respiratory dysfunction. To understand the respiratory deficits, ongoing studies are histologically analyzing the diaphragm neuromuscular junction, phrenic and hypoglossal nerves, as well as phrenic and hypoglossal motor nuclei. Preliminary nerve analysis of the hypoglossal and phrenic nerves reveals significant axonal pathology. In conclusion, WBP analysis and preliminary histological nerve data reveals respiratory dysfunction in the Atxn7 266Q/+ mouse model. Support or Funding Information Funding: R01 HD099486‐01; 1R21NS098131‐01
Amyotrophic Lateral Sclerosis (ALS) is a devastating and fatal neurodegenerative disease with no current cure. Respiratory failure is the leading cause of death in ALS. Death occurs3–5 years after diagnosis when patients with ALS ultimately succumb to inadequate ventilation, hypoxia, and respiratory failure. Several genes are associated with ALS. One of these genes encodes optineurin (OPTN) which is associated with neurodegeneration in both ALS and glaucoma. Optineurin has multiple roles in various biochemical pathways such as regulation of inflammation and autophagy. However, the exact mechanism by which loss of OPTN results in progressive neural degeneration and respiratory failure in ALS is still unclear. In order to understand the impact of OPTN deficiency on respiratory function, our goal was to study the respiratory pathophysiology in the Optn −/− mouse. The hypothesis driving this work is that the Optn −/− mouse has respiratory insufficiency due to degeneration of the respiratory motor unit – motor neuron, nerve, neuromuscular junction and muscle. Physiological, histological and molecular outcome measures were used to assess the impact of OPTN on the respiratory system. We used whole body plethysmography (WBP) to assess breathing at baseline and during a respiratory challenge with hypercapnic and hypoxic conditions (FiCO 2 : 0.07, FiO 2 : 0.10; nitrogen balance). During the respiratory challenge, compared to the WT mice, Optn −/− mice had significantly lower tidal volume, minute ventilation, peak inspiratory flow, and peak expiratory flow starting at 6 months of age indicating weakened muscle strength. Furthermore, throughout the challenge period Optn −/− mice spent a greater amount of time in apnea indicating pathology in the respiratory control centers. The weakness and pathology in control of breathing during the respiratory challenge progresses as the mice age. At 1 year of age, Optn −/− mice have stunted growth accompanied by reduced diaphragm size compared to WT mice. Postmortem immunohistochemical studies of the medulla reveal Optn −/− mice have fewer hypoglossal motor neurons. Finally, the hypoglossal (XII) nerves of Optn −/− mice had significantly reduced g‐ratio which indicates pathology and decompaction of myelin sheaths. Within the XII nerve, there are an increase in both the number of mitochondria and area of mitochondria. These along with elevated levels of LC3‐II to LC3‐I indicate reduced mitophagy. In conclusion, the Optn −/− ALS mouse model displays motor neuron pathology, increased nerve demyelination and aberrant control of breathing leading to respiratory insufficiency.
Abstract Background Telomere maintenance mechanisms are required to enable the replicative immortality of malignant cells. While most cancers activate the enzyme telomerase, a subset of cancers uses telomerase-independent mechanisms termed alternative lengthening of telomeres (ALT). ALT occurs via homology-directed-repair mechanisms and is frequently associated with ATRX mutations. We previously showed that a subset of adult glioblastoma (GBM) patients with ATRX-expressing ALT-positive tumors harbored loss-of-function mutations in the SMARCAL1 gene, which encodes an annealing helicase involved in replication fork remodeling and the resolution of replication stress. However, the causative relationship between SMARCAL1 deficiency, tumorigenesis, and de novo telomere synthesis is not understood. Methods We used a patient-derived ALT-positive GBM cell line with native SMARCAL1 deficiency to investigate the role of SMARCAL1 in ALT-mediated de novo telomere synthesis, replication stress, and gliomagenesis in vivo. Results Inducible rescue of SMARCAL1 expression suppresses ALT indicators and inhibits de novo telomere synthesis in GBM and osteosarcoma cells, suggesting that SMARCAL1 deficiency plays a functional role in ALT induction in cancers that natively lack SMARCAL1 function. SMARCAL1-deficient ALT-positive cells can be serially propagated in vivo in the absence of detectable telomerase activity, demonstrating that the SMARCAL1-deficient ALT phenotype maintains telomeres in a manner that promotes tumorigenesis. Conclusions SMARCAL1 deficiency is permissive to ALT and promotes gliomagenesis. Inducible rescue of SMARCAL1 in ALT-positive cell lines permits the dynamic modulation of ALT activity, which will be valuable for future studies aimed at understanding the mechanisms of ALT and identifying novel anticancer therapeutics that target the ALT phenotype.
Pompe disease (OMIM 232300) is an autosomal recessive disorder caused by mutations in the gene encoding acid α-glucosidase (GAA) (EC 3.2.1.20),the enzyme responsible for hydrolyzing lysosomal glycogen.The primary cellular pathology is lysosomal glycogen accumulation in cardiac muscle, skeletal muscle, and motor neurons, which ultimately results in cardiorespiratory failure.However, the severity of pathology and its impact on clinical outcomes are poorly described in smooth muscle.The advent of enzyme replacement therapy (ERT) in 2006 has improved clinical outcomes in infantile-onset Pompe disease patients.Although ERT increases patient life expectancy and ventilator free survival, it is not entirely curative.Persistent motor neuron pathology and weakness of respiratory muscles, including airway smooth muscles, contribute to the need for mechanical ventilation by some patients on ERT.Some patients on ERT continue to experience life-threatening pathology to vascular smooth muscle, such as aneurysms or dissections within the aorta and cerebral arteries.Better characterization of the disease impact on smooth muscle will inform treatment development and help anticipate later complications.This review summarizes the published knowledge of smooth muscle pathology associated with Pompe disease in animal models and in patients.
ABSTRACT Spinocerebellar ataxia type 7 (SCA7) is an autosomal-dominant neurodegenerative disorder caused by a CAG repeat expansion in the coding region of the ataxin-7 gene. Infantile-onset SCA7 patients display extremely large repeat expansions (>200 CAGs) and exhibit progressive ataxia, dysarthria, dysphagia and retinal degeneration. Severe hypotonia, aspiration pneumonia and respiratory failure often contribute to death in affected infants. To better understand the features of respiratory and upper airway dysfunction in SCA7, we examined breathing and putative phrenic and hypoglossal neuropathology in a knock-in mouse model of early-onset SCA7 carrying an expanded allele with 266 CAG repeats. Whole-body plethysmography was used to measure awake spontaneously breathing SCA7-266Q knock-in mice at baseline in normoxia and during a hypercapnic/hypoxic respiratory challenge at 4 and 8 weeks, before and after the onset of disease. Postmortem studies included quantification of putative phrenic and hypoglossal motor neurons and microglia, and analysis of ataxin-7 aggregation at end stage. SCA7-266Q mice had profound breathing deficits during a respiratory challenge, exhibiting reduced respiratory output and a greater percentage of time in apnea. Histologically, putative phrenic and hypoglossal motor neurons of SCA7 mice exhibited a reduction in number accompanied by increased microglial activation, indicating neurodegeneration and neuroinflammation. Furthermore, intranuclear ataxin-7 accumulation was observed in cells neighboring putative phrenic and hypoglossal motor neurons in SCA7 mice. These findings reveal the importance of phrenic and hypoglossal motor neuron pathology associated with respiratory failure and upper airway dysfunction, which are observed in infantile-onset SCA7 patients and likely contribute to their early death.
Introduction Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome.
Amyotrophic Lateral Sclerosis (ALS) is a devastating and fatal neurodegenerative disease with no current cure. Patients with ALS die 3–5 years after diagnosis when they ultimately succumb to inadequate ventilation, hypoxia, and respiratory failure. Several genes associated with ALS have recently been discovered. One of these genes encodes optineurin (OPTN) which is associated with neurodegeneration in both ALS and glaucoma. Optineurin has multiple roles in various biochemical pathways such as regulation of inflammation and autophagy. Through these functions, OPTN appears to be neuroprotective but the exact mechanism by which loss of OPTN results in progressive neural degeneration and respiratory failure in ALS is still unclear. Since respiratory pathology is a significant cause of morbidity and mortality in ALS, this study sought to characterize the respiratory pathology in a novel ALS mouse model – the Optn −/− mouse. The hypothesis driving this work is that the Optn −/− mouse has respiratory insufficiency due to degeneration of the respiratory motor unit – motor neuron, nerve, neuromuscular junction and muscle. Whole body plethysmography (WBP) was used to assess breathing at baseline and during a respiratory challenge with hypercapnic and hypoxic conditions (FiCO 2 : 0.07, FiO 2 : 0.10; nitrogen balance). During the respiratory challenge, compared to the WT mice, Optn −/− mice had significantly lower peak inspiratory flow and peak expiratory flow. Peak inspiratory flow and peak expiratory flow are indirect measures of inspiratory and expiratory muscle strength. Furthermore, throughout the challenge period Optn −/− mice spent a greater amount of time in apnea indicating pathology in the respiratory control centers. The weakness and pathology in control of breathing during the respiratory challenge progresses as the mice age. Post mortem immunohistochemical studies of the neuromuscular junctions within the diaphragm showed that Optn −/− mice had fragmented synaptotagmin staining indicating presynaptic degeneration. Finally, the hypoglossal nerves of Optn −/− mice had significantly reduced g‐ratio which indicates pathology and decompaction of myelin sheaths. In conclusion, the Optn −/− ALS mouse model displays respiratory insufficiency, aberrant control of breathing, and increased nerve demyelination. Support or Funding Information R21 NS098131‐02 (MKE) and K08HD077040‐07 (MKE) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
Amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia (SCA) are neurodegenerative disorders that result in progressive motor dysfunction and ultimately lead to respiratory failure. Rodent models of neurodegenerative disorders provide a means to study the respiratory motor unit pathology that results in respiratory failure. In addition, they are important for pre-clinical studies of novel therapies that improve breathing, quality of life, and survival. The goal of this review is to compare the respiratory phenotype of two neurodegenerative disorders that have different pathological origins, but similar physiological outcomes. Manuscripts reviewed were identified using specific search terms and exclusion criteria. We excluded manuscripts that investigated novel therapeutics and only included those manuscripts that describe the respiratory pathology. The ALS manuscripts describe pathology in respiratory physiology, the phrenic and hypoglossal motor units, respiratory neural control centers, and accessory respiratory muscles. The SCA rodent model manuscripts characterized pathology in overall respiratory function, phrenic motor units and hypoglossal motor neurons. Overall, a combination of pathology in the respiratory motor units and control centers contribute to devastating respiratory dysfunction.
