Immunoblotting of single cell types isolated from frozen sections by laser microdissection

The molecular basis of skeletal muscle weakness in a mouse model of inflammatory myopathy

OBJECTIVE

It is generally believed that muscle weakness in patients with polymyositis and dermatomyositis is due to autoimmune and inflammatory processes. However, it has been observed that there is a poor correlation between the suppression of inflammation and a recovery of muscle function in these patients. This study was undertaken to examine whether nonimmune mechanisms also contribute to muscle weakness. In particular, it has been suggested that an acquired deficiency of AMP deaminase 1 (AMPD1) may be responsible for muscle weakness in myositis.

METHODS

We performed comprehensive functional, behavioral, histologic, molecular, enzymatic, and metabolic assessments before and after the onset of inflammation in a class I major histocompatibility complex (MHC)-transgenic mouse model of autoimmune inflammatory myositis.

RESULTS

Muscle weakness and metabolic disturbances were detectable in the mice prior to the appearance of infiltrating mononuclear cells. Force contraction analysis of muscle function revealed that weakness was correlated with AMPD1 expression and was myositis specific. Decreasing AMPD1 expression resulted in decreased muscle strength in healthy mice. Fiber typing suggested that fast-twitch muscles were converted to slow-twitch muscles as myositis progressed, and microarray results indicated that AMPD1 and other purine nucleotide pathway genes were suppressed, along with genes essential to glycolysis.

CONCLUSION

These data suggest that an AMPD1 deficiency is acquired prior to overt muscle inflammation and is responsible, at least in part, for the muscle weakness that occurs in the mouse model of myositis. AMPD1 is therefore a potential therapeutic target in myositis.

Activation of the endoplasmic reticulum stress response in autoimmune myositis: potential role in muscle fiber damage and dysfunction

OBJECTIVE

The etiology and pathogenesis of human inflammatory myopathies remain unclear. Findings of several studies suggest that the degree of inflammation does not correlate consistently with the severity of clinical disease or of structural changes in the muscle fibers, indicating that nonimmune pathways may contribute to the pathogenesis of myositis. This study was undertaken to investigate these pathways in myositis patients and in a class I major histocompatibility complex (MHC)-transgenic mouse model of myositis.

METHODS

We examined muscle tissue from human myositis patients and from class I MHC-transgenic mice for nonimmune pathways, using biochemical, immunohistochemical, and gene expression profiling assays.

RESULTS

Up-regulation of class I MHC in skeletal muscle fibers was an early and consistent feature of human inflammatory myopathies. Class I MHC staining in muscle fibers of myositis patients showed both cell surface and a reticular pattern of internal reactivity. The pathways of endoplasmic reticulum (ER) stress response, the unfolded protein response (glucose-regulated protein 78 pathway), and the ER overload response (NF-kappaB pathway) were significantly activated in muscle tissue of human myositis patients and in the mouse model. Ectopic expression of wild-type mouse class I MHC (H-2K(b)) but not degradable glycosylation mutants of H-2K(b) induced ER stress response in C(2)C(12) skeletal muscle cells.

CONCLUSION

These results indicate that the ER stress response may be a major nonimmune mechanism responsible for skeletal muscle damage and dysfunction in autoimmune myositis. Strategies to interfere with this pathway may have therapeutic value in patients with this disease.

Use of a new adhesive film for the preparation of multi-purpose fresh-frozen sections from hard tissues, whole-animals, insects and plants

A method for preparing thin fresh-frozen sections from large samples and hard tissues is described and the applications are shown. A new adhesive film is introduced to produce the frozen sections. The sample is frozen in a cooled hexane or liquid nitrogen, and then freeze-embedded with 4-5% carboxymethyl cellulose (CMC) in the coolant. A specially prepared adhesive film is fastened to the cut surface of the sample in order to support the section and cut slowly with a disposable tungsten carbide blade. The adhesive film is made of a thin plastic film and an adhesive before use. This method produces 2-microm thick fresh-frozen sections from a large sample, bone or tooth. The "film-section" i.e. the section attached to the adhesive film, can be used for many types of studies such as histology, general histochemistry, enzyme histochemistry, immunohistochemistry, in situ hybridization, elemental analysis, and autoradiography for water-soluble materials. Immunohistochemistry and in situ hybridization can be carried out with nonfixed and undecalcified sections. The section on the adhesive film can be transferred to a glass slide and mounted under a cover slip, and stained sections can be examined with an optical microscope at high magnification. This method is also useful for preparing frozen sections from samples of fish, insects, and plants. Furthermore, samples of particular areas can be collected from the film-section by means of a laser microdissection technique. The multiple possible applications of the adhesive film render it highly useful for studies in biological and medico-dental fields.