Mitochondrial abnormalities in myofibrillar myopathies.

Histological mitochondrial changes are generally found to be associated with late onset myofibrillar myopathies (MFMs). How these changes contribute to the pathogenesis of MFMs is unknown. Mitochondrial changes, including COX-deficient fibers (n = 8), biochemical activities of respiratory chain complexes (n = 7), and multiple mtDNA deletions by long-range PCR (n = 9) were examined in patients with genetically confirmed MFMs [MYOT (n = 2), DES (n = 1), ZASP (n = 2), FLNC (n = 4)] and compared with age and sex matched normal controls (n = 27) and patients with a mitochondrial disorder with multiple mtDNA deletions due to nuclear genetic defects (n = 8). In 2 MFM patients, micro dissected fibers were analyzed for multiple mtDNA deletions by nested long-range PCR. The COX-deficient fibers only partly corresponded with fibers containing myofibrillar accumulations. In total, there was no difference in the percentage of COX-deficient fibers in MFM patients and normal controls. However, the percentage of COX-deficient fibers was significantly higher in 3 MFM patients. Two MFM patients but none of the controls had multiple mtDNA deletions. Nested long-range PCR detected multiple mtDNA deletions only in COX-deficient fibers. Citrate synthase activities in MFM patients were 1.5-fold increased by compared to those in controls, suggesting initiation of mitochondrial alterations. However, it is unclear whether this is a direct consequence of MFM pathology. *both authors contributed equally to the manuscript.

Identification of a core domain within the proregion of bone morphogenetic proteins that interacts with the dimeric, mature domain.

Proregions of bone morphogenetic proteins (BMPs) fulfill important biological functions as intramolecular chaperones and for extracellular targeting of the mature signal ligand. Knowledge of the structures of the proregions would contribute to a more comprehensive picture of the biological activities of the pro-forms of BMP growth factors. In this study, a protease resistant core domain of the proregions of three BMPs was identified. For a more detailed analysis, the core domain of the BMP-2 proregion was recombinantly produced. Unfolding/refolding experiments and spectroscopic analyses proved that the core domain can be obtained as a folded entity. Binding of the core domain to the mature growth factor was demonstrated by SPR. Via peptide microarray analysis, residues within the core fragment could be identified that engage in binding to the dimeric, mature domain. Our study reveals that diverse members of the BMP family share a common, independently folding core domain within the large proregions peculiar to TGF-ß superfamily members that may serve as a scaffold for folding and assembly of the dimeric proprotein complexes.

Oxidative folding of nerve growth factor can be mediated by the pro-peptide of neurotrophin-3.

We have previously shown that the pro-peptide of human nerve growth factor (NGF) facilitates oxidative folding of the mature part. For the analysis of functional specificities of the pro-peptides of NGF and the related neurotrophin-3 (NT-3) with respect to structure formation, chimeric proteins with swapped pro-peptides were generated. Neither the structure nor the stability of the mature domains was influenced by the heterologous pro-peptides. For the pro-peptide of NT-3 fused to the mature part of NGF, stabilization of the pro-peptide moiety by the NGF part was observed. Folding kinetics and renaturation yields of this chimeric protein were comparable to those of proNGF. Our results demonstrate functional interchangeability between the pro-peptides of NGF and NT-3 with respect to their role in assisting oxidative folding of the mature part.

Oculopharyngeal muscular dystrophy as a rare cause of dysphagia.

Oculopharyngeal muscular dystrophy (OPMD) is a rare cause for late-onset dysphagia. OPMD normally follows an autosomal dominant inheritance. Herein we describe a rare case of an autosomal recessive inheritance of OPMD. An 80-year-old male presented with progressive dysphagia, frequent aspiration and change of voice getting inarticulate and hoarse. Physical examination showed ptosis of the right eyelid. Endoscopic and manometric investigation revealed a nonspecific motility disorder with hypopharyngeal esophageal hypotension. The severity of dysphagia became apparent when significant aspiration occurred during a barium swallow. Magnetic resonance imaging of the head ruled out a malignant or cerebral ischemic process. Based on the neurological examination, neurogenic muscular dystrophy was suspected and DNA analysis was performed. The analysis confirmed the extremely rare diagnosis of an autosomal recessive inheritance pattern of OPMD with homozygous (GCN)6(GCN)4(GCN) expansion of the poly-(A) binding protein nuclear 1 gene. As OPMD normally follows an autosomal dominant inheritance, consanguinity of the patient's parents was suspected.

Functional relevance of mitochondrial abnormalities in sporadic inclusion body myositis.

Cytochrome c oxidase (COX)-deficient fibers and multiple mitochondrial DNA (mtDNA) deletions are frequent findings in sporadic inclusion body myositis (s-IBM). However, the functional impact of these defects is not known. We investigated oxygen desaturation during exercise using the forearm exercise test, accumulation of lactate during exercise using a cycle ergometry test and mitochondrial changes (COX-deficient fibers, biochemical activities of respiratory chain complexes, multiple mtDNA deletions by long-range polymerase chain reaction) in 10 patients with s-IBM and compared the findings with age and sex-matched normal and diseased controls (without mitochondrial disorders) as well as patients with mitochondrial disorder due to nuclear gene defects resulting in multiple mtDNA deletions (MITO group). The mean age of the s-IBM patients was 68.2 ± 5.7 years (range: 56-75). Patients with s-IBM had statistically significantly reduced oxygen desaturation (ΔsO2) during the handgrip exercise (p<0.05) and elevated peak serum lactate levels during cycle ergometry compared to normal controls (p<0.05). The percentage of COX-deficient fibers in s-IBM and MITO patients was significantly increased compared to normal controls (p<0.01). Five out of nine s-IBM patients had multiple mtDNA deletions. Thirty-three percent of s-IBM patients showed an increased citrate synthase content and decreased activities of complex IV (COX). The biochemical pattern of respiratory chain complexes in patients with s-IBM and MITO was similar. Histopathological analysis showed similar changes in s-IBM and MITO due to nuclear gene defects. Functional tests reflecting mitochondrial impairment suggest a contribution of mitochondrial defects to disease-related symptoms such as fatigue and exertion-induced symptoms.

The pro-form of BMP-2 interferes with BMP-2 signalling by competing with BMP-2 for IA receptor binding.

Pro-forms of growth factors have received increasing attention since it was shown that they can affect both the maturation and functions of mature growth factors. Here, we assessed the biological function of the pro-form of bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor beta (TGFbeta)/BMP superfamily. The role of the 263 amino acids of the pro-peptide is currently unclear. In order to obtain an insight into the function of the pro-form (proBMP-2), the ability of proBMP-2 to induce alkaline phosphatase (AP), a marker enzyme for cells differentiating into osteoblasts, was tested. Interestingly, in contrast to mature BMP-2, proBMP-2 did not lead to induction of AP. Instead, proBMP-2 inhibited the induction of AP by BMP-2. This result raised the question of whether proBMP-2 may compete with mature BMP-2 for receptor binding. ProBMP-2 was found to bind to the purified extracellular ligand binding domain (ECD) of BMPR-IA, a high-affinity receptor for mature BMP-2, with a similar affinity as mature BMP-2. Binding of proBMP-2 to BMPR-IA was confirmed in cell culture by cross-linking proBMP-2 to BMPR-IA presented on the cell surface. In contrast to this finding, proBMP-2 did not bind to the ECD of BMPR-II. ProBMP-2 also differed from BMP-2 in its capacity to induce p38 and Smad phosphorylation. The data presented here suggest that the pro-domain of BMP-2 can alter the signalling properties of the growth factor by modulating the ability of the mature part to interact with the receptors.