Teresa Gidaro

MyoD expression restores defective myogenic differentiation of human mesoangioblasts from inclusion-body myositis muscle.

Inflammatory myopathies (IM) are acquired diseases of skeletal muscle comprising dermatomyositis (DM), polymyositis (PM), and inclusion-body myositis (IBM). Immunosuppressive therapies, usually beneficial for DM and PM, are poorly effective in IBM. We report the isolation and characterization of mesoangioblasts, vessel-associated stem cells, from diagnostic muscle biopsies of IM. The number of cells isolated, proliferation rate and lifespan, markers expression, and ability to differentiate into smooth muscle do not differ among normal and IM mesoangioblasts. At variance with normal, DM and PM mesoangioblasts, cells isolated from IBM, fail to differentiate into skeletal myotubes. These data correlate with lack in connective tissue of IBM muscle of alkaline phosphatase (ALP)-positive cells, conversely dramatically increased in PM and DM. A myogenic inhibitory basic helix–loop–helix factor B3 is highly expressed in IBM mesoangioblasts. Indeed, silencing this gene or overexpressing MyoD rescues the myogenic defect of IBM mesoangioblasts, opening novel cell-based therapeutic strategies for this crippling disorder.

An Italian family with inclusion-body myopathy and frontotemporal dementia due to mutation in the VCP gene

Mutations of the valosin‐containing protein gene (VCP) are responsible for autosomal‐dominant hereditary inclusion‐body myopathy associated with frontotemporal dementia and Pagets disease of bone. We identified the p.R155C missense mutation in the VCP gene segregating in an Italian family with three affected siblings, two of whom had a progressive myopathy associated with dementia, whereas one exhibited a progressive myopathy and preclinical signs of Pagets disease of bone. Our study demonstrates that VCP mutations are found in patients of Italian background and may lead to a variable clinical phenotype even within the same kinship. Muscle Nerve, 2007

Hyposialylation of neprilysin possibly affects its expression and enzymatic activity in hereditary inclusion-body myopathy muscle.

Autosomal recessive hereditary inclusion‐body myopathy (h‐IBM) is caused by mutations of the UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase gene, a rate‐limiting enzyme in the sialic acid metabolic pathway. Previous studies have demonstrated an abnormal sialylation of glycoproteins in h‐IBM. h‐IBM muscle shows the abnormal accumulation of proteins including amyloid‐β (Aβ). Neprilysin (NEP), a metallopeptidase that cleaves Aβ, is characterized by the presence of several N‐glycosylation sites, and changes in these sugar moieties affect its stability and enzymatic activity. In the present study, we found that NEP is hyposialylated and its expression and enzymatic activity reduced in all h‐IBM muscles analyzed. In vitro, the experimental removal of sialic acid by Vibrio Cholerae neuraminidase in cultured myotubes resulted in reduced expression of NEP. This was most likely because of a post‐translational modification consisting in an abnormal sialylation of the protein that leads to its reduced stability. Moreover, treatment with Vibrio Cholerae neuraminidase was associated with an increased immunoreactivity for Aβ mainly in the form of distinct cytoplasmic foci within myotubes. We hypothesize that, in h‐IBM muscle, hyposialylated NEP has a role in hampering the cellular Aβ clearing system, thus contributing to its abnormal accumulation within vulnerable fibers and possibly promoting muscle degeneration.

α-Dystroglycan does not play a major pathogenic role in autosomal recessive hereditary inclusion-body myopathy

Mutations of the GNE gene are responsible for autosomal recessive hereditary inclusion-body myopathy (HIBM). In this study we searched for the presence of any significant abnormality of alpha-dystroglycan (alpha-DG), a highly glycosylated component of the dystrophin-glycoprotein complex, in 5 HIBM patients which were previously clinically and genetically characterized. Immunocytochemical and immunoblot analysis showed that alpha-DG extracted from muscle biopsies was normally expressed and displayed its typical molecular mass. Immunoblot analysis on the wheat germ lectin-enriched glycoprotein fraction of muscles and primary myotubes showed a reduced amount of alpha-DG in 4 out of 5 HIBM patients, compared to normal and other diseased muscles. However, such altered lectin-binding behaviour, possibly reflecting a partial hyposialylation of alpha-DG, did not affect the laminin binding properties of alpha-DG. Therefore, the subtle changes within the alpha-DG glycosylation pattern, detected in HIBM muscles, likely do not play a key pathogenic role in this disorder.

Isolation and characterization of mesoangioblasts from facioscapulohumeral muscular dystrophy muscle biopsies.

Facioscapulohumeral muscular dystrophy (FSHD) is the third most frequent inherited muscle disease. Because in FSHD patients the coexistence of affected and unaffected muscles is common, myoblasts expanded from unaffected FSHD muscles have been proposed as suitable tools for autologous cell transplantation. Mesoangioblasts are a new class of adult stem cells of mesodermal origin, potentially useful for the treatment of primitive myopathies of different etiology. Here, we report the isolation and characterization of mesoangioblasts from FSHD muscle biopsies and describe morphology, proliferation, and differentiation abilities of both mesoangioblasts and myoblasts derived from various affected and unaffected muscles of nine representative FSHD patients. We demonstrate that mesoangioblasts can be efficiently isolated from FSHD muscle biopsies and expanded to an amount of cells necessary to transplant into an adult patient. Proliferating mesoangioblasts from all muscles examined did not differ from controls in terms of morphology, phenotype, proliferation rate, or clonogenicity. However, their differentiation ability into skeletal muscle was variably impaired, and this defect correlated with the overall disease severity and the degree of histopathologic abnormalities of the muscle of origin. A remarkable differentiation defect was observed in mesoangioblasts from all mildly to severely affected FSHD muscles, whereas mesoangioblasts from morphologically normal muscles showed no myogenic differentiation block. Our study could open the way to cell therapy for FSHD patients to limit muscle damage in vivo through the use of autologous mesoangioblasts capable of reaching damaged muscles and engrafting into them, without requiring immune suppression or genetic correction in vitro.

Neprilysin participates in skeletal muscle regeneration and is accumulated in abnormal muscle fibres of inclusion body myositis.

Neprilysin (NEP, EP24.11), a metallopeptidase originally shown to modulate signalling events by degrading small regulatory peptides, is also an amyloid‐β‐ (Aβ) degrading enzyme. We investigated a possible role of NEP in inclusion body myositis (IBM) and other acquired and hereditary muscle disorders and found that in all myopathies NEP expression was directly associated with the degree of muscle fibre regeneration. In IBM muscle, NEP protein was also strongly accumulated in Aβ‐bearing abnormal fibres. In vitro, during the experimental differentiation of myoblasts, NEP protein expression was regulated at the post‐transcriptional level with a rapid increase in the early stage of myoblast differentiation followed by a gradual reduction thereafter, coincident with the progression of the myogenic programme. Treatment of differentiating muscle cells with the NEP inhibitor dl‐3‐mercapto‐2‐benzylpropanoylglycine resulted in impaired differentiation that was mainly associated with an abnormal regulation of Akt activation. Therefore, NEP may play an important role during muscle cell differentiation, possibly through the regulation, either directly or indirectly, of the insulin‐like growth factor I‐driven myogenic programme. In IBM muscle increased NEP may be instrumental in (i) reducing the Aβ accumulation in vulnerable fibres and (ii) promoting a repair/regenerative attempt of muscle fibres possibly through the modulation of insulin‐like growth factor I‐dependent pathways.

TWEAK in inclusion-body myositis muscle: possible pathogenic role of a cytokine inhibiting myogenesis

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 exert pleiotropic effects, including regulation of myogenesis. Sporadic inclusion-body myositis (IBM) is the most common muscle disease of the elderly population and leads to severe disability. IBM mesoangioblasts, different from mesoangioblasts in other inflammatory myopathies, display a myogenic differentiation defect. The objective of the present study was to investigate TWEAK-Fn14 expression in IBM and other inflammatory myopathies and explore whether TWEAK modulation affects myogenesis in IBM mesoangioblasts. TWEAK, Fn14, and NF-κB expression was assessed by immunohistochemistry and Western blot in cell samples from both muscle biopsies and primary cultures. Mesoangioblasts isolated from samples of IBM, dermatomyositis, polymyositis, and control muscles were treated with recombinant human TWEAK, Fn14-Fc chimera, and anti-TWEAK antibody. TWEAK-RNA interference was performed in IBM and dermatomyositis mesoangioblasts. TWEAK levels in culture media were determined by enzyme-linked immunosorbent assay. In IBM muscle, we found increased TWEAK-Fn14 expression. Increased levels of TWEAK were found in differentiation medium from IBM mesoangioblasts. Moreover, TWEAK inhibited myogenic differentiation of mesoangioblasts. Consistent with this evidence, TWEAK inhibition by Fn14-Fc chimera or short interfering RNA induced myogenic differentiation of IBM mesoangioblasts. We provide evidence that TWEAK is a negative regulator of human mesoangioblast differentiation. Dysregulation of the TWEAK-Fn14 axis in IBM muscle may induce progressive muscle atrophy and reduce activation and differentiation of muscle precursor cells.

Atrophy, Fibrosis, and Increased PAX7-Positive Cells in Pharyngeal Muscles of Oculopharyngeal Muscular Dystrophy Patients

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant inherited dystrophy caused by an abnormal trinucleotide repeat expansion in the poly(A)-binding-protein-nuclear 1 (PABPN1) gene. Primary muscular targets of OPMD are the eyelid elevator and pharyngeal muscles, including the cricopharyngeal muscle (CPM), the progressive involution of which leads to ptosis and dysphagia, respectively. To understand the consequences of PABPN1 polyalanine expansion in OPMD, we studied muscle biopsies from 14 OPMD patients, 3 inclusion body myositis patients, and 9 healthy controls. In OPMD patient CPM (n = 6), there were typical dystrophic features with extensive endomysial fibrosis and marked atrophy of myosin heavy-chain IIa fibers. There were more PAX7-positive cells in all CPM versus other muscles (n = 5, control; n = 3, inclusion body myositis), and they were more numerous in OPMD CPM versus control normal CPM without any sign of muscle regeneration. Intranuclear inclusions were present in all OPMD muscles but unaffected OPMD patient muscles (i.e. sternocleidomastoid, quadriceps, or deltoid; n = 14) did not show evidence of fibrosis, atrophy, or increased PAX7-positive cell numbers. These results suggest that the specific involvement of CPM in OPMD might be caused by failure of the regenerative response with dysfunction of PAX7-positive cells and exacerbated fibrosis that does not correlate with the presence of PABPN1 inclusions.

Increased aging in primary muscle cultures of sporadic inclusion-body myositis.

Ageing is thought to participate to the pathogenesis of sporadic inclusion-body myositis (s-IBM). Although the regenerative potential of s-IBM muscle is reduced in vivo, age-related abnormalities of satellite cells possibly accounting for the decline of muscle repair have not been demonstrated. Here we show that proliferation rate and clonogenicity of s-IBM myoblasts are significantly lower and doubling time is longer than normal age-matched controls, indicating that proliferative capacity of s-IBM muscles becomes exhausted earlier. Telomere shortening is detected in s-IBM cells suggesting premature senescence. Differently from controls, s-IBM myoblasts show increased active beta-catenin mainly localized within myonuclei, indicating active Wnt stimulation. After many rounds of muscle growth, only s-IBM myoblasts accumulate congophilic inclusions and immunoreactive Abeta(1-40) deposits. Therefore, s-IBM myoblasts seem to have a constitutively impaired regenerative capacity and the intrinsic property, upon sufficient aging in vitro, to accumulate Abeta. Our results might be valuable in understanding molecular mechanisms associated with muscle aging underlying the defective regeneration of s-IBM muscle and provide new clues for future therapeutic strategies.

Analysis of NCAM helps identify unusual phenotypes of hereditary inclusion-body myopathy

Background: Hereditary inclusion-body myopathy or distal myopathy with rimmed vacuoles (h-IBM/DMRV) is due to mutations of the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene, which codes for an enzyme of the sialic acid biosynthetic pathway. By Western blot (WB) analysis, we have previously shown that in h-IBM/DMRV muscle, the neural cell adhesion molecule (NCAM) has increased electrophoretic mobility that reflects reduced sialylation of the protein. Objective: To identify patients with h-IBM/DMRV with atypical clinical or pathologic phenotype using NCAM analysis and the possible cellular mechanism associated with the overall abnormal sialylation of NCAM observed in this disorder. Methods: WB analysis of NCAM was performed on muscle biopsies of 84 patients with an uncharacterized muscle disorder who were divided in the following 2 groups: 1) 46 patients with a proximal muscle weakness in whom the main limb-girdle muscular dystrophy syndromes had been ruled out; and 2) 38 patients with a distal distribution of weakness in whom a neurogenic affection had been excluded. Patients in whom a reduced sialylation of NCAM was suspected were studied for the presence of GNE mutations. Results: In 3 patients, we found that NCAM had increased electrophoretic mobility, thus suggesting an abnormal sialylation of the protein. The genetic study demonstrated that they all carried pathogenic GNE mutations. Further studies demonstrated that hyposialylated NCAM, showing increased electrophoretic mobility on WB, is expressed by nonregenerating fibers in h-IBM/DMRV muscle. Conclusions: WB analysis of NCAM may be instrumental in the identification of h-IBM/DMRV with atypical clinical or pathologic features.