Activation of the alternative complement pathway and production of factor H by skeletal myotubes

Human keratinocytes produce the complement inhibitor factor H: synthesis is regulated by interferon-gamma

Locally synthesized complement is believed to play an important role in host defense and inflammation at organ level. In the epidermis, keratinocytes have so far been shown to synthesize two complement components, C3 and factor B. Here, we studied the synthesis of factor H by human keratinocytes. We also studied the regulation of factor H synthesis in keratinocytes by several cytokines, namely IL-1alpha, IL-2, IL-6, TGF-beta1, TNF-alpha and IFN-gamma. Human keratinocytes expressed factor H mRNA and constitutively released small amounts of factor H protein into the culture medium. This release was strongly upregulated by IFN-gamma but not by other cytokines tested. Western blot analysis revealed that IFN-gamma augments the synthesis of both molecular species, factor H (FH; 155kDa) and factor H-like protein-1 (FHL-1; 45kDa), of factor H. Factor H released in response to IFN-gamma was functionally active. In conclusion, we demonstrate that keratinocytes are capable of synthesizing factor H and that this synthesis is regulated by IFN-gamma.

Complement C5 in experimental autoimmune encephalomyelitis (EAE) facilitates remyelination and prevents gliosis

Activation of the classical complement system is known to play a central role in autoimmune demyelination. We have analyzed the role of complement component C5 in experimental autoimmune encephalomyelitis (EAE) using C5-deficient (C5-d) and C5-sufficient (C5-s) mice. Both groups of mice displayed early onset EAE, a short recovery phase, and similar stable chronic courses. However, in contrast to the clinical similarities, marked differences were apparent by histopathology. During acute EAE in C5-d, a delay in inflammatory cell infiltration and tissue damage was observed along with restricted lesion areas, which in C5-s mice were more extensive and diffuse. More striking were the differences in chronic lesions. In C5-d mice, inflammatory demyelination and Wallerian degeneration were followed by axonal depletion and severe gliosis, while in C5-s, the same initial signs were followed by axonal sparing and extensive remyelination. In C5-d, immunohistochemistry and Western blotting showed an increase in glial fibrillary acidic protein and a decrease in neurofilament protein, proteolipid protein, and several pro-inflammatory markers. These results in the EAE model indicate that absence of C5 resulted in fiber loss and extensive scarring, whereas presence of C5-favored axonal survival and more efficient remyelination.

Complement 3 deficiency and oral prednisolone improve strength and prolong survival of laminin alpha2-deficient mice

Complement deposition and macrophages are common in biopsies of children with muscular dystrophy. While the presumed roles of complement and macrophages have been those of scavenger to remove and clear necrotic fibers, there is some evidence that they play a primary role in the pathogenesis of these diseases. Here, we explore the role of complement in the pathogenesis of the most severe animal model of congenital dystrophy, the dy-/- mouse, which is laminin alpha2-deficient. We generated animals deficient in both C3 and laminin alpha2. C3 is the third component of the complement cascade and is required for activation of either the classical or alternative pathways. Thirty-three percent of the dy-/-:C3+ mice (n=59) died before 24 weeks while only 14% of the dy-/-:C3-/- (n=29) mice died (p=0.04). Absolute forepaw strength was 25-30% greater for the dy-/-:C3-/- mice up to 20 weeks of age (p<0.05 compared to complement-sufficient). Forepaw strength adjusted for weight also showed significant differences with C3-/- mice being stronger up to 20 weeks (p<0.05). However, by 24 weeks, the two groups did not differ for strength. Next, we treated 20 mice with twice weekly oral prednisolone. Survival at 24 weeks for the prednisolone treated dy-/- mice (C3-/- or C3+) was 90% (p=0.04). This work shows that complement insufficiency and weekly prednisone prolong survival and improve strength of the laminin alpha2-deficient mouse. This work suggests that the complement system may contribute directly to the pathogenesis of this form of dystrophy. Because complement activity may be modified pharmacologically, this work may have implications for treatment of children with congenital muscular dystrophy secondary to laminin alpha2 deficiency.

Complement activation alters myocellular sodium homeostasis during polymicrobial sepsis

OBJECTIVE

To determine whether complement activation alters sodium homeostasis in fast-twitch skeletal muscles during sepsis, and if protein kinase-C is involved in this process.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory.

SUBJECTS

Male Sprague-Dawley rats weighing 60-75 g.

INTERVENTIONS

Rats underwent cecal ligation and puncture (CLP) or sham-operation with or without soluble complement receptor-1 treatment. Soluble complement receptor-1 (20 mg/kg) was administered intraperitoneally 5 mins before operation. Twenty-four hours after operation, fast-twitch extensor digitorum longus muscles were isolated and incubated in normal Krebs-Henseleit buffer (pH 7.4). In addition, extensor digitorum longus muscles isolated from normal rats were incubated for 1 hr in the Krebs-Henseleit buffer media containing normal rat sera, zymosan-activated (4 or 10 mg/mL) rat sera, or heat-inactivated rat sera. Ten percent diluted rat sera were used as a complement source in all groups. Last, extensor digitorum longus muscles isolated from normal rats were incubated for 1 hr in the Krebs-Henseleit buffer media containing zymosan-activated or heat-inactivated rat sera in the presence of protein kinase-C inhibitors (i.e., 4 microM GF109203X or 5 microM rottlerin). Soluble C5b-9 complex concentrations in zymosan-activated human sera were determined by enzyme-linked immunosorbent assay to evaluate the degree of complement activation induced by zymosan.

MEASUREMENTS AND MAIN RESULTS

Incubated extensor digitorum longus muscles from CLP, sham-operated, or normal rats were used to measure intracellular Na+ and K+ contents ([Na+]i or [K+]i). Polymicrobial sepsis, as produced by CLP, markedly increased [Na+]i and [Na+]i/[K+]i ratios in fast-twitch extensor digitorum longus muscles 24 hrs after CLP compared with sham operation. Administration of soluble recombinant complement receptor 1 before operation significantly decreased myocellular [Na+]i and [Na+]i/[K+]i ratios. Zymosan profoundly elevated soluble C5b-9 concentrations in human sera in vitro. Sublytic zymosan-activated rat sera significantly increased myocellular [Na+]i and [Na+]i/[K+]i ratios relative to heat-inactivated rat sera. No difference in myocellular [Na+]i and [Na+]i/[K+]i ratios was observed when we used 4 mg/mL compared with 10 mg/mL of zymosan for activation. Last, incubation of extensor digitorum longus muscles with GF109203X or rottlerin significantly attenuated increases in myocellular [Na+]i and [Na+]i/[K+]i ratios induced by sublytic zymosan-activated rat sera.

CONCLUSIONS

Polymicrobial sepsis alters sodium homeostasis in fast-twitch skeletal muscles, which is significantly attenuated by administration of soluble complement receptor 1. Protein kinase-C inhibition completely blocks changes in myocellular [Na+]i and [Na+]i/[K+]i ratios induced by sublytic zymosan-activated rat sera. Collectively, these results suggest that an inappropriate activation of complement is, at least in part, responsible for changes in skeletal muscle sodium homeostasis during sepsis, and activation of PKC is one of the intracellular signaling pathways by which complement activation alters myocellular sodium homeostasis.

Extraocular muscle is defined by a fundamentally distinct gene expression profile

Skeletal muscle fibers are defined by patterned covariation of key traits that determine contractile and metabolic characteristics. Although the functional properties of most skeletal muscles result from their proportional content of a few conserved muscle fiber types, some, typically craniofacial, muscles exhibit fiber types that appear to lie outside the common phenotypic range. We analyzed gene expression profiles of three putative muscle classes, limb, masticatory, and extraocular muscle (EOM), in adult mice by high-density oligonucleotide arrays. Pairwise comparisons using conservative acceptance criteria identified expression differences in 287 genes between EOM and limb and/or masticatory muscles. Use of significance analysis of microarrays methodology identified up to 400 genes as having an EOM-specific expression pattern. Genes differentially expressed in EOM reflect key aspects of muscle biology, including transcriptional regulation, sarcomeric organization, excitation-contraction coupling, intermediary metabolism, and immune response. These patterned differences in gene expression define EOM as a distinct muscle class and may explain the unique response of these muscles in neuromuscular diseases.

Sublytic complement attack increases intracellular sodium in rat skeletal muscle

BACKGROUND

Although excessive complement activation and deranged sodium homeostasis in skeletal muscle are characteristic in sepsis, their relationship has not been examined. This study was designed to determine if sublytic complement activation can directly mediate changes in myocellular sodium content.

MATERIALS AND METHODS

Fast-twitch extensor digitorum longus muscles were freshly isolated from infant rats. Unsensitized muscles were incubated at 30 degrees C for 60 min in the media containing 10% human or rat serum under conditions of no complement activation, activation by zymosan, inactivation by heat, C7 or C9 deficiency, selective inhibition of complement pathway, and inhibition of Na(+)-K(+) ATPase by ouabain. Intracellular sodium ([Na(+)](i)) and potassium ([K(+)](i)) contents of the muscles, myocellular ATP, and LDH release from the muscles were then determined.

RESULTS

Normal human serum significantly increased [Na(+)](i) and the [Na(+)](i)/[K(+)](i) ratio in the muscles as well as zymosan-activated serum. Heat inactivation, C7 deficiency, and inhibition of the alternative pathway completely abolished the cationic changes. Average LDH release was identical in all groups and less than 6%. Complement activation did not impair ouabain-sensitive Na(+)-K(+) ATPase activity in the muscles or alter myocellular ATP. Thus, the observed alterations are not likely due to dysfunction of Na(+)-K(+) pump or depletion of myocellular energy. Instead, alterations in [Na(+)](i) were dependent upon the amount of C9 added to C9-deficient serum, which suggests that the alterations are likely dependent on transmembrane pores created by membrane attack complexes (MAC).

CONCLUSIONS

Sublytic amounts of MAC formed as a result of complement activation can directly alter [Na(+)](i) in ex vivo skeletal muscle.

Analysis of the promoter region of the murine complement factor H gene

We have used the luciferase system to assay basal promoter activity of the murine factor H gene. Based on the results from luciferase assays with clones of 13 nested deletions, a 242-bp region that appeared to contain an enhancer element was subcloned upstream of a heterologous promoter and was shown to enhance transcription. A 26-bp fragment from this region was shifted in electrophoretic mobility assays, and this fragment contains a consensus sequence for the adenovirus major late transcription factor/upstream stimulatory factor (MLTF/USF). This fragment had enhancing activity in a minimal factor H promoter construct, demonstrating that it is a major enhancer of the factor H gene in murine liver cells.

Expression of the complement alternative pathway by human myoblasts in vitro: biosynthesis of C3, factor B, factor H and factor I

In this study, we demonstrate expression in vitro of complement alternative pathway components C3, factor B, factor H and factor I by normal human myoblasts and human rhabdomyosarcoma cell lines CRL1558 and HTB153. Proteins in culture supernatants were detected by Western (protein) blot analysis and biosynthetic labeling followed by immunoprecipitation experiments, and quantified by ELISA. Newly secreted proteins were structurally and functionally similar to their serum counterparts. An additional polypeptide of 43 kDa with factor H immunoreactivity was detected, which could correspond to the N-terminal truncated form found in plasma. Protein expression was correlated with mRNA expression by reverse transcriptase-polymerase chain reaction analysis. The major proteins of complement alternative pathway C3, factor B and factor H were produced constitutively by skeletal muscle cells at a rate of 50 to 150 ng/10(6) cells/ml and factor I was expressed 20 ng/10(6) cells/ml. These syntheses in vitro were regulated by inflammatory cytokines. Interferon-gamma significantly upregulated C3, factor B and factor H expression, but had no effect on factor I production. Interleukin-1 beta strongly enhanced C3 and factor B production and had a weak enhancing or no effect on factor I and factor H secretion. Human myoblast cell lines constitute an interesting model to analyze complement biosynthesis by human skeletal muscle cells. Local complement expression by skeletal muscle in vivo may be implicated in some muscular inflammatory or pathological processes.