Differentially co-expressed myofibre transcripts associated with abnormal myofibre proportion in chronic obstructive pulmonary disease

BACKGROUND

Skeletal muscle dysfunction is a common extrapulmonary manifestation of chronic obstructive pulmonary disease (COPD). Alterations in skeletal muscle myosin heavy chain expression, with reduced type I and increased type II myosin heavy chain expression, are associated with COPD severity when studied in largely male cohorts. The objectives of this study were (1) to define an abnormal myofibre proportion phenotype in both males and females with COPD and (2) to identify transcripts and transcriptional networks associated with abnormal myofibre proportion in COPD.

METHODS

Forty-six participants with COPD were assessed for body composition, strength, endurance and pulmonary function. Skeletal muscle biopsies from the vastus lateralis were assayed for fibre-type distribution and cross-sectional area via immunofluorescence microscopy and RNA-sequenced to generate transcriptome-wide gene expression data. Sex-stratified k-means clustering of type I and IIx/IIax fibre proportions was used to define abnormal myofibre proportion in participants with COPD and contrasted with previously defined criteria. Single transcripts and weighted co-expression network analysis modules were tested for correlation with the abnormal myofibre proportion phenotype.

RESULTS

Abnormal myofibre proportion was defined in males with COPD (n = 29) as <18% type I and/or >22% type IIx/IIax fibres and in females with COPD (n = 17) as <36% type I and/or >12% type IIx/IIax fibres. Half of the participants with COPD were classified as having an abnormal myofibre proportion. Participants with COPD and an abnormal myofibre proportion had lower median handgrip strength (26.1 vs. 34.0 kg, P = 0.022), 6-min walk distance (300 vs. 353 m, P = 0.039) and forced expiratory volume in 1 s-to-forced vital capacity ratio (0.42 vs. 0.48, P = 0.041) compared with participants with COPD and normal myofibre proportions. Twenty-nine transcripts were associated with abnormal myofibre proportions in participants with COPD, with the upregulated NEB, TPM1 and TPM2 genes having the largest fold differences. Co-expression network analysis revealed that two transcript modules were significantly positively associated with the presence of abnormal myofibre proportions. One of these co-expression modules contained genes classically associated with muscle atrophy, as well as transcripts associated with both type I and type II myofibres, and was enriched for genetic loci associated with bone mineral density.

CONCLUSIONS

Our findings indicate that there are significant transcriptional alterations associated with abnormal myofibre proportions in participants with COPD. Transcripts canonically associated with both type I and type IIa fibres were enriched in a co-expression network associated with abnormal myofibre proportion, suggesting altered transcriptional regulation across multiple fibre types.

Phase II trial of Gliadel plus O6-benzylguanine (O6-BG) for patients with recurrent glioblastoma multiforme

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Background. The major mechanism of resistance to alkylnitrosourea therapy involves the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) which removes chloroethylation or methylation damage from the O6-position of guanine. O6-BG is an AGT substrate that inhibits AGT by suicide inactivation. A previous phase III randomized, placebo-controlled trial has shown that Gliadel wafer significantly prolongs 6-month survival (55.5% for Gliadel vs. 35.6% for placebo) and median survival (28 weeks for Gliadel vs. 20 weeks for placebo) in patients with recurrent glioblastoma multiforme (GBM) (Brem et al 1995). Despite the success of Gliadel in prolonging survival we may be able to improve on this success by depleting AGT. Methods. Thus, we have designed a phase 2 trial where we define the activity and the toxicity of Gliadel in combination with a 5-day infusion of O6-BG in patients with recurrent GBM. In a prior study the O6-BG dose found to be effective in depleting tumor AGT activity at 48 hours was an IV bolus of 120 mg/m2 over 1 hour followed by a continuous infusion of 30 mg/m2/d for 48 hours. In order to guarantee depletion of tumor AGT activity for at least 5 days after Gliadel placement, this O6-BG bolus was repeated on days 3 and 5 while continuing the infusion. Results. To date, 24 patients have been enrolled out of a planned accrual of 50 patients. Seventeen of these patients received prior nitrosourea therapy. The 6-month survival is 68% and the median survival is 36 weeks. The adverse events include the following: 2 episodes of CSF leak (8%), 4 episodes of wound infection at craniotomy site (16%), 5 episodes of grade ≥ 3 seizures (21%) and 3 episodes of hyponatremia (12%). These adverse events were similar in frequency to those seen in patients receiving Gliadel in prior placebo-controlled Gliadel trials. Conclusions. Thus far, this data demonstrates an increase in the efficacy of Gliadel when combined with O6-BG. Twenty-six additional patients will be enrolled for a total accrual of 50 patients.

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Effects of growth inhibitors and ultraviolet irradiation on F pili

The effects of chloramphenicol, nalidixic acid, mitomycin C, NaCN, and ultraviolet irradiation at 253.7 nm on F pili production by Escherichia coli cells was studied by electron microscopy. The results show that cells contain pools of pili protein, and that assembly does not require synthesis of protein or deoxyribonucleic acid (DNA). NaCN (2 x 10(-2)m) prevents the reappearance of pili and causes existing pili to disappear quickly from the cell surface. This suggests that energy is used in the assembly of pili and to retain pili on the cell. Cells irradiated with high doses (10(4)ergs/mm(2)) of 253. 7 nm light produce fewer pili, and these are shorter than normal. Dose-response curves for number of pili per cell and length of pili resemble single hit kinetics, showing 37% survival at 10(4) ergs/mm(2) and 2 x 10(4) ergs/mm(2), respectively. This suggests that DNA is at the site where pili are produced, and that it may be involved in the assembly of pili.

Some effects of temperature on the growth of F pili

The effect of temperature on the production of F pili by an F(+) strain of Escherichia coli B/r was studied by electron microscopy and by a technique involving serum-blocking power. The latter method is based on the ability of F pili to adsorb F pili antibody which inhibits male-specific phage infection. The total amount of pili in a sample was estimated by serum-blocking power; the length of F pili and number per cell was determined by electron microscopy. Cell extracts prepared by sonic oscillation lacked serum-blocking power, suggesting that F pili are not present in the cytoplasm. The number of F pili per cell varied with the growth temperature, but the average length of F pili remained constant. Maximum number of pili per cell occurs between 37 and 42 C; below 37 C the number decreases, reaching zero at about 25 C. When cells are grown at 37 C, blended, and resuspended in fresh media at 25 C, they make F pili. These pili are probably assembled from a pool of subunits that were synthesized during growth at 37 C. The rates of assembly at 25 and 37 C, as judged by the rate of increase in length of F pili, are similar. When cells were grown at 25 C and shifted up to 37 C, there was a 30-min lag in pili production followed by a period of rapid outgrowth. When cells were shifted down from 37 to 20 C, outgrowth (assembly) of pili ceased, and approximately 50% of the attached pili were released in 2 min. No release was observed when cells were shifted to 0 C. This suggests that pili may be released from the cell by a mechanism that requires metabolic activity, but not the outgrowth of F pili.