Leukemia inhibitory factor ameliorates muscle fiber degeneration in the mdx mouse.

Although the muscles of the mdx mouse lack dystrophin, the protein absent in muscles of humans affected with Duchenne muscular dystrophy (DMD), the only mdx muscle to degenerate in a manner similar to those of DMD boys is the diaphragm. We have previously shown that leukemia inhibitory factor (LIF) is a trauma factor that enhances muscle repair in vivo and, when applied exogenously, increases the fiber size of mdx skeletal muscle. Furthermore, we developed a controlled release device for LIF based on a calcium alginate rod (release rate about 0.5% per day). These rods were sutured to the abdominal surface of the hemidiaphragm of mdx mice 3 months old. At age 6 months the mice were killed and the diaphragm muscles fixed and sectioned. The sections showed obvious muscle degeneration at 3 months of age in mdx mouse diaphragms and further degeneration at 6 months in saline-perfused muscle. Hemidiaphragm muscles continuously exposed to LIF over the same period contained more normal myofibers, larger regenerated fibers, and less adipose tissue and other non-contractile tissue. Morphometric analysis of the diaphragm sections was carried out. The LIF-treated animals showed a significant increase in fiber number and size compared to saline rod controls. The amount of nonmuscle (connective tissue and adipose tissue) was significantly reduced and the maximum force-producing capacity of isolated diaphragm muscle strips was higher in LIF-treated mice. The results demonstrate that LIF treatment ameliorates the dystrophic abnormalities in mdx mouse diaphragm.

Effects of LIF dose and laminin plus fibronectin on axotomized sciatic nerves.

Leukemia inhibitory factor (LIF), a cytokine which has neurotrophic and myotrophic activities, has been shown to enhance nerve regeneration and consequent return of muscle function in the entubulation model of sciatic nerve repair. Fibronectin (FN) and laminin (LN) are two extracellular matrix (ECM) components that, when combined, promote axon growth in the entubulation model. The aim of this study was to determine the optimal LIF dose and the efficacy of FN plus LN administered either alone or simultaneously with the optimal LIF dose. We found that at 12 weeks following nerve repair, a single 10 ng LIF dose produced the largest medial gastrocnemius (MG) muscle mass (P < 0.0001) and maximum force contraction (P < 0.001). The diameter of the axons in the FN plus LN group were significantly greater than for saline (P < 0.001) and the LIF dose groups (P < 0.01). When 10 ng LIF was combined with FN plus LN, the MG muscle mass was significantly greater than the optimal LIF dose (P < 0.05), suggesting an additive effect. Our findings support the view that combinations of factors, which perhaps act on complementary mechanisms for nerve regeneration, will be required to maximally potentiate nerve regeneration and return of muscle function after nerve injury.

Anterograde transport of leukemia inhibitory factor within transected sciatic nerves.

Disappointing functional recovery following peripheral nerve repair can be improved by neurotrophic growth factors. Leukemia inhibitory factor (LIF) is unique in that it has independent neurotrophic and myotrophic actions. The aim of this study was to explain this finding by establishing the existence of anterograde axonal transport of LIF from the site of nerve division to denervated muscles. Using 125I LIF, administered topically via an entubulation repair of divided rat sciatic nerve, we monitored its subsequent distribution by measuring the radioactivity associated with nerve segments and denervated muscles. We established that LIF preferentially accumulated in denervated muscles, a process we could reduce by 70% after tightly ligating the intervening nerve, confirming the presence of anterograde axonal transport. This was most likely an active mode of transport that ceased approximately 24 h after nerve division, establishing a narrow clinical time frame within which the myotrophic action of LIF could be optimized following nerve repair.

Leukaemia inhibitory factor (LIF) production in a mouse model of spinal trauma.

A model of spinal trauma was developed where spinal neurones of adult mice were exposed to the excitotoxic glutamate analogue beta-N-oxylamino-L-alanine (L-BOAA). After 24 h, the injured neurones received a single dose of [125I]-LIF at the same site of the spinal cord, and 2 h later, tissues were removed to assess the distribution of leukaemia inhibitory factor (LIF). There was a significant increase in LIF binding to the injured region of the spinal cord over saline controls, and this corresponded with a significant increase in LIF mRNA expression in the same region of the cord. There was a change in the expression of ciliary neurotrophic factor, but the expression of cardiotrophin-1 (CT-1) and the common receptor subunit LIF receptor beta (LIFRbeta) did not change after neurotoxin treatment. The results add to the evidence that LIF plays a significant role in the response of adult neuronal tissue to injury.

A chloroplast processing enzyme involved in precursor maturation shares a zinc-binding motif with a recently recognized family of metalloendopeptidases.

Nuclear-encoded proteins targeted to the chloroplast are typically synthesized with N-terminal transit peptides which are proteolytically removed upon import. Structurally related proteins of 145 and 143 kDa copurify with a soluble chloroplast processing enzyme (CPE) that cleaves the precursor for the major light-harvesting chlorophyll a/b binding protein and have been implicated in the maturation of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase and acyl carrier protein. The 145- and 143-kDa proteins have not been found as a heterodimer and thus may represent functionally independent isoforms encoded by separate genes. Here we describe the primary structure of a 140-kDa polypeptide encoded by cDNAs isolated by using antibodies raised against the 145/143-kDa doublet. The 140-kDa polypeptide contains a transit peptide, and strikingly, a His-Xaa-Xaa-Glu-His zinc-binding motif that is conserved in a recently recognized family of metalloendopeptidases, which includes Escherichia coli protease III, insulin-degrading enzyme, and subunit beta of the mitochondrial processing peptidase. Identity of 25-30%, concentrated near the N terminus of the 140-kDa polypeptide, is found with these proteases. Expression of CPE in leaves is not light dependent. Indeed, transcripts are present in dark-grown plants, and the 145/143-kDa doublet and proteolytic activity are both found in etioplasts, as well as in root plastids. Thus, CPE appears to be a necessary component of the import machinery in photosynthetic and nonphotosynthetic tissues, and it may function as a general stromal processing peptidase in plastids.

Protection from noise-induced hearing loss by prior exposure to a nontraumatic stimulus: role of the middle ear muscles.

Recent evidence suggests that prior exposure to a moderate-level acoustic stimulus can reduce damage due to later exposure to the same stimulus at high intensity [Canlon et al., Hear. Res. 34, 197-200 (1988)]. To test the role of the middle ear muscles (MEMs) in this phenomenon, Mongolian gerbils were conditioned by exposure to a two-octave band of noise (1414-5656 Hz) at 81 dB SPL for 3 weeks. Either immediately afterward, or following a one week rest period, they were exposed to the same stimulus at 110 dB SPL for one hour. The ABR thresholds of these animals were compared to those seen in animals exposed at 110 dB SPL without conditioning. The MEMs of one ear in each subject were cut, to determine their role in any noise trauma protection effects. In the unoperated ears, conditioning without a recovery period did not alter the effects of the 110 dB stimulus. Conditioning followed by a one week recovery period reduced both temporary (TTS) and permanent (PTS) threshold shift. MEM section had no effect on either TTS or PTS in unconditioned subjects, and did not alter the reduction in TTS or PTS seen with conditioning. It is concluded that the noise trauma resistance provided by acoustic conditioning is not mediated by the MEMs.

Primary malignant fibrous histiocytoma of the retroperitoneum.

A 38 year old woman presenting with minimal digestive symptoms was found on ultrasound and computerized tomography scanning to have a large, solid, uniform mass arising in the region of the right adrenal gland. Preoperative investigations indicated a non-functioning tumour. At operation a well-circumscribed, ovoid tumour was removed and found subsequently to be a malignant fibrous histiocytoma arising adjacent to the right adrenal gland. It is believed that sarcomas arising in the retroperitoneum should be included in the differential diagnosis of masses presumed to be adrenal tumours on scanning. The limitations of computerized tomography scanning in distinguishing between benign and malignant tumours and between adrenal and juxta-adrenal masses should be recognized. Tumour size is the best indicator of malignancy and it is recommended that non-functioning tumours greater than 5 cm in diameter be presumed malignant until proven otherwise histologically. Surgical removal of all non-functioning retroperitoneal masses greater than 5 cm in diameter is therefore recommended.

Ultrastructural changes in testes of the snapping turtle, Chelydra serpentina in relation to plasma testosterone, delta 5-3 beta-hydroxysteroid dehydrogenase, and cholesterol.

Ultrastructural changes in the testes of the common snapping turtle, Chelydra serpentina, were observed throughout the year. Plasma testosterone levels were measured and compared with the occurrence of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), cholesterol, and steroidogenic ultrastructural features (smooth endoplasmic reticulum (SER), mitochondria with tubular cristae) in Sertoli and Leydig cells. The testosterone level is highest in May and October (mating) and relatively low during the rest of the year. Fluctuations in 3 beta-HSD and cholesterol are consistent with the interpretation that the Leydig cells are potentially active throughout the year. They undergo very little ultrastructural change, (tubular SER to vesiculate and loss of golgi during spermatogenesis and in the winter). Sertoli cells are active only during spermatogenesis from May through October and become inactive until the next cycle; 3 beta-HSD, cholesterol and ultrastructural features change more drastically in the Sertoli cells than in the Leydig cells. These results are discussed with reference to the hypothesis that testosterone of Leydig origin is concerned mainly with mating behavior and that of Sertoli origin with spermatogenesis and maturation of sperm.