Transcriptome assessment of the Pompe (Gaa-/-) mouse spinal cord indicates widespread neuropathology.

Pompe disease, caused by deficiency of acid alpha-glucosidase (GAA), leads to widespread glycogen accumulation and profound neuromuscular impairments. There has been controversy, however, regarding the role of central nervous system pathology in Pompe motor dysfunction. We hypothesized that absence of GAA protein causes progressive activation of neuropathological signaling, including pathways associated with cell death. To test this hypothesis, genomic data (Affymetrix Mouse Gene Array 2.0ST) from the midcervical spinal cord in 6 and 16 mo old Pompe (Gaa-/-) mice were evaluated (Broad Institute Molecular Signature Database), along with spinal cord histology. The midcervical cord was selected because it contains phrenic motoneurons, and phrenic-diaphragm dysfunction is prominent in Pompe disease. Several clinically important themes for the neurologic etiology of Pompe disease emerged from this unbiased genomic assessment. First, pathways associated with cell death were strongly upregulated as Gaa-/- mice aged, and motoneuron apoptosis was histologically verified. Second, proinflammatory signaling was dramatically upregulated in the Gaa-/- spinal cord. Third, many signal transduction pathways in the Gaa-/- cervical cord were altered in a manner suggestive of impaired synaptic function. Notably, glutamatergic signaling pathways were downregulated, as were "synaptic plasticity pathways" including genes related to neuroplasticity. Fourth, many genes and pathways related to cellular metabolism are dysregulated. Collectively, the data unequivocally confirm that systemic absence of GAA induces a complex neuropathological cascade in the spinal cord. Most importantly, the results indicate that Pompe is a neurodegenerative condition, and this underscores the need for early therapeutic intervention capable of targeting the central nervous system.

Osteoarthritis in temporomandibular joint of Col2a1 mutant mice.

OBJECTIVE: Col2a1 gene mutations cause premature degeneration of knee articular cartilage in disproportionate micromelia (Dmm) and spondyloepiphesial dysplasia congenita (sedc) mice. The present study analyses the temporomandibular joint (TMJ) in Col2a1 mutant mice in order to provide an animal model of TMJ osteoarthritis (OA) that may offer better understanding of the progression of this disease in humans. DESIGN: Dmm/+ mice and controls were compared at two, six, nine and 12 months. Craniums were fixed, processed to paraffin sections, stained with Safranin-O/Fast Green, and analysed with light microscopy. OA was quantified using a Mankin scoring procedure. Unfolded protein response (UPR) assay was performed and immunohistochemistry (IHC) was used to assay for known OA biomarkers. RESULTS: Dmm/+ TMJs showed fissuring of condylar cartilage as early as 6 months of age. Chondrocytes were clustered, leaving acellular regions in the matrix. Significant staining of HtrA1, Ddr2 and Mmp-13 was observed in Dmm/+ mice (p<0.01). We detected upregulation of the UPR in knee but not TMJ. CONCLUSIONS: Dmm/+ mice are subject to early-onset OA in the TMJ. We observed upregulation of biomarkers and condylar cartilage degradation concomitant with OA. An upregulated UPR may exacerbate the onset of OA. The Dmm/+ mouse TMJ is a viable model for the study of the progression of OA in humans.

Redox regulation of diaphragm proteolysis during mechanical ventilation.

Prevention of oxidative stress via antioxidants attenuates diaphragm myofiber atrophy associated with mechanical ventilation (MV). However, the specific redox-sensitive mechanisms responsible for this remain unknown. We tested the hypothesis that regulation of skeletal muscle proteolytic activity is a critical site of redox action during MV. Sprague-Dawley rats were assigned to five experimental groups: 1) control, 2) 6 h of MV, 3) 6 h of MV with infusion of the antioxidant Trolox, 4) 18 h of MV, and 5) 18 h of MV with Trolox. Trolox did not attenuate MV-induced increases in diaphragmatic levels of ubiquitin-protein conjugation, polyubiquitin mRNA, and gene expression of proteasomal subunits (20S proteasome alpha-subunit 7, 14-kDa E2, and proteasome-activating complex PA28). However, Trolox reduced both chymotrypsin-like and peptidylglutamyl peptide hydrolyzing (PGPH)-like 20S proteasome activities in the diaphragm after 18 h of MV. In addition, Trolox rescued diaphragm myofilament protein concentration (mug/mg muscle) and the percentage of easily releasable myofilament protein independent of alterations in ribosomal capacity for protein synthesis. In summary, these data are consistent with the notion that the protective effect of antioxidants on the diaphragm during MV is due, at least in part, to decreasing myofilament protein substrate availability to the proteasome.

Antioxidant administration attenuates mechanical ventilation-induced rat diaphragm muscle atrophy independent of protein kinase B (PKB Akt) signalling.

Oxidative stress promotes controlled mechanical ventilation (MV)-induced diaphragmatic atrophy. Nonetheless, the signalling pathways responsible for oxidative stress-induced muscle atrophy remain unknown. We tested the hypothesis that oxidative stress down-regulates insulin-like growth factor-1-phosphotidylinositol 3-kinase-protein kinase B serine threonine kinase (IGF-1-PI3K-Akt) signalling and activates the forkhead box O (FoxO) class of transcription factors in diaphragm fibres during MV-induced diaphragm inactivity. Sprague-Dawley rats were randomly assigned to one of five experimental groups: (1) control (Con), (2) 6 h of MV, (3) 6 h of MV with infusion of the antioxidant Trolox, (4) 18 h of MV, (5) 18 h of MV with Trolox. Following 6 h and 18 h of MV, diaphragmatic Akt activation decreased in parallel with increased nuclear localization and transcriptional activation of FoxO1 and decreased nuclear localization of FoxO3 and FoxO4, culminating in increased expression of the muscle-specific ubiquitin ligases, muscle atrophy factor (MAFbx) and muscle ring finger-1 (MuRF-1). Interestingly, following 18 h of MV, antioxidant administration was associated with attenuation of MV-induced atrophy in type I, type IIa and type IIb/IIx myofibres. Collectively, these data reveal that the antioxidant Trolox attenuates MV-induced diaphragmatic atrophy independent of alterations in Akt regulation of FoxO transcription factors and expression of MAFbx or MuRF-1. Further, these results also indicate that differential regulation of diaphragmatic IGF-1-PI3K-Akt signalling exists during the early and late stages of MV.

Mechanical ventilation promotes redox status alterations in the diaphragm.

Oxidative stress is an important mediator of diaphragm muscle atrophy and contractile dysfunction during prolonged periods of controlled mechanical ventilation (MV). To date, specific details related to the impact of MV on diaphragmatic redox status remain unknown. To fill this void, we tested the hypothesis that MV-induced diaphragmatic oxidative stress is the consequence of both an elevation in intracellular oxidant production in conjunction with a decrease in the antioxidant buffering capacity. Adult rats were assigned to one of two experimental groups: 1) control or 2) 12 h of MV. Compared with controls, diaphragms from MV animals demonstrated increased oxidant production, diminished total antioxidant capacity, and decreased glutathione levels. Heme oxygenase-1 (HO-1) mRNA and protein levels increased (23.0- and 5.1-fold, respectively) following MV. Thioredoxin reductase-1 and manganese superoxide dismutase mRNA levels were also increased in the diaphragm following MV (2.4- and 1.6-fold, respectively), although no change was detected in the levels of either protein. Furthermore, copper-zinc superoxide dismutase and glutathione peroxidase mRNA were not altered following MV, although protein content decreased -1.3- and -1.7-fold, respectively. We conclude that MV promotes increased oxidant production and impairment of key antioxidant defenses in the diaphragm; collectively, these changes contribute to the MV-induced oxidative stress in this key inspiratory muscle.