Double-stranded RNA-dependent protein kinase deficiency protects the heart from systolic overload-induced congestive heart failure

BACKGROUND

Double-stranded RNA-dependent protein kinase (PKR) is a eukaryotic initiation factor 2α kinase that inhibits mRNA translation under stress conditions. PKR also mediates inflammatory and apoptotic signaling independently of translational regulation. Congestive heart failure is associated with cardiomyocyte hypertrophy, inflammation, and apoptosis, but the role of PKR in left ventricular hypertrophy and the development of congestive heart failure has not been examined.

METHODS AND RESULTS

We observed increased myocardial PKR expression and translocation of PKR into the nucleus in humans and mice with congestive heart failure. To determine the impact of PKR on the development of congestive heart failure, PKR knockout and wild-type mice were exposed to pressure overload produced by transverse aortic constriction. Although heart size increased similarly in wild-type and PKR knockout mice after transverse aortic constriction, PKR knockout mice exhibited very little pulmonary congestion, well-preserved left ventricular ejection fraction and contractility, and significantly less myocardial fibrosis compared with wild-type mice. Bone marrow-derived cells from wild-type mice did not abolish the cardiac protective effect observed in PKR knockout mice, whereas bone marrow-derived cells from PKR knockout mice had no cardiac protective effect in wild-type mice. Mechanistically, PKR knockout attenuated transverse aortic constriction-induced tumor necrosis factor-α expression and leukocyte infiltration and lowered cardiac expression of proapoptotic factors (Bax and caspase-3), so that PKR knockout hearts were more resistant to transverse aortic constriction-induced cardiomyocyte apoptosis. PKR depletion in isolated cardiomyocytes also conferred protection against tumor necrosis factor-α- or lipopolysaccharide-induced apoptosis.

CONCLUSION

PKR is a maladaptive factor upregulated in hemodynamic overload that contributes to myocardial inflammation, cardiomyocyte apoptosis, and the development of congestive heart failure.

Phenotype of an X-linked retinitis pigmentosa family with a novel splice defect in the RPGR gene

PURPOSE

To assess the clinical phenotype in a Swedish family with X-linked retinitis pigmentosa (XLRP) resulting from a novel splice defect in the RPGR gene.

METHODS

RPGR mutation analysis was performed in one family with XLRP, and several individuals from the family were examined clinically.

RESULTS

The causative mutation in the family was demonstrated to be a single base-pair change at the splice donor site in intron 7 that resulted in skipping of the complete exon 7 in the mature RPGR transcript. The aberrant mRNA is predicted to produce an RPGR protein with an in-frame deletion of 53 amino acids, corresponding to an RCC1-homology repeat. Clinical studies that included ophthalmological examination and full-field electroretinography showed that this splice mutation resulted in a comparatively less severe form of RP.

CONCLUSIONS

Correlation of a causative RPGR genotype with clinical findings in hemizygotes and carrier heterozygotes is an important step toward predictive diagnosis and should assist in the development of gene-based therapies in the future.