Increased expression of CNTF receptor alpha in denervated human skeletal muscle.

The functional receptor for ciliary neurotrophic factor (CNTF) is comprised of a CNTF binding entity termed CNTF receptor alpha (CNTFRalpha), and 2 signaling molecules called LIF receptor beta and gp130. CNTFRalpha can be released from the cell surface; the soluble form can confer CNTF responsiveness to cells. CNTFRalpha has recently been localized to several nonneuronal cell types including rat skeletal muscle fibers. In this study we examined the expression pattern of CNTFRalpha in normal, denervated and dystrophic human muscle. In muscle biopsies from 12 normal subjects, 16 cases of neurogenic muscular atrophy, 4 cases of Duchenne muscular dystrophy, and 4 cases of limb girdle dystrophy, CNTFRalpha mRNA levels were determined by Northern blotting. Transcript levels were significantly increased in cases of neurogenic atrophy compared to normal controls and dystrophic muscle. By nonradioactive in situ hybridization, CNTFRalpha transcripts were detected in the sarcoplasm of both normal sized and atrophic muscle fibers. In addition, soluble CNTFRalpha was elevated 4.4-fold in the urine of ALS patients compared to normal adults. These results suggest that the expression of CNTFRalpha in human skeletal muscle fibers is regulated by innervation. This regulation appears to be selective, because CNTFRalpha mRNA was not increased in dystrophic human muscle. Increased CNTFRalpha could confer higher sensitivity to CNTF during neurodegeneration or nerve fiber regeneration.

CNTF and its receptor subunits in human gliomas.

Ciliary neurotrophic factor (CNTF) promotes the survival of various neuronal cell populations. It is produced by astrocytes and influences the development and differentiation of glial cells. CNTF and related neuropoietic cytokines affect growth and differentiation of various neoplasms. Moreover, they induce the reactive transformation of astrocytes (gliosis) and influence growth and differentiation of neuroectodermal tumor cell lines in vitro. However, their role in gliomas is largely unknown. We studied the expression of CNTF and its receptor subunits in human astrocytomas and glioblastomas. In more than 95% of the tumors, CNTF transcripts were found by RNAase protection assay; in more than 80% of the cases, tumor cells were CNTF immunoreactive. CNTF receptor alpha (CNTFR alpha), the specific component of the tripartite CNTF receptor system, was detectable by Northern blot analysis in 80% of the cases. In situ hybridization revealed CNTFR alpha mRNA in the cytoplasm of neoplastic cells. Transcripts of the remaining two components of the CNTF receptor system, gp130 and LIFR beta, were found by Northern blotting in 83% and 70% of the tumors, respectively. Simultaneous expression of CNTF and all its receptor components was detected in approximately half of the tumors. These results indicate that CNTF and its receptor components are expressed by human glioma cells. The simultaneous expression of ligands and receptor subunits suggests that CNTF might act on human glioma cells via an auto- or paracrine mechanism.