The Mechanism Of Ciliary Neurotrophic Factor (cntf) To Regulate Energy Balance

Ciliary neurotrophic factor (CNTF) is a member of the cytokine family structurally related to leukemia inhibitory factor, IL-6 and other cytokines. Administration of CNTF can suppresses appetite and cause weight loss in animals just like leptin. It is found that CNTF can cause preferential loss of fat in genetically obese mice (ob/ob, db/db). Especially, CNTF is also effective in diet-induced obesity mice that are more representative of human obesity, and which are resistant to leptin. In this study, we investigated the related mechanism of CNTF regulating energy balance from energy expenditure and energy intake.Enhancing energy expenditure is an important way to loss weight. Recent years, uncoupling proteins (UCPs), expressed on the inner mitochondrial membrane, are thought to play a major role in energy expenditure. UCPs serve to uncouple respirations with ATP synthesis in mitochondrial. Accordingly, energy is wasted as heat. Three major uncoupling proteins have been identified in mammals—UCP1, exclusively in brown adipose tissue (BAT); UCP2, expressed ubiquitously; UCP3, predominantly in muscle and BAT. BAT is recognized as the primary site of thermogenesis in rodents, but adult humans, unlike rodents, do not have large, distinct depots of brown adipose, tissue. Skeletal muscle, on the other hand, represents up to 40% of total body weight and is endowed with significant mitochondrial capacity, causing many researchers to investigate its contribution to adaptive thermogenesis.Therefore, in our study we sought to assess whether CNTF could increase energy expenditure through enhancing UCPs level in mice BAT and gastrocnemius muscle. The results from western blotting showed that CNTF systemic administration increased mice UCP1 level of interscapular BAT. The UCP1 protein level of normal mice, intraperitoneally injected with CNTF (0.2μg/g/day) for 6 days, was more than twice that of saline-treated mice (230% vs control, P＜0.01). The results from RT-PCR showed that CNTF acute treatment had no effects on the expression of UCPs in BAT, but it increased the expression of UCP3 in gastrocnemius (156% vs control, P＜0.05). Intraperitoneal injection of 0.2mg/kg CNTF for 3 days elevated the expression of UCP1 in BAT (153% vs control, P＜0.05) and UCP3 in gastrocnemius (154% vs control, P＜0.05), but the mRNA level of UCP2 and UCP3 in BAT was not affected. These results suggestd CNTF increased thermogenic activity in gastrocnemius muscle by UCP3 and brown adipose tissue only by UCP1.As to energy intake, cumulative evidences show that a hypothalamic circuitry comprising of a number of orexigenic and anorectic neuropeptides is critical for food intake. Among this signals, neuropeptide Y (NPY) is the prime candidate to stimulate feeding. NPY is produced in the arcuate nucleus (ARC) and released in the paraventricular nucleus (PVN) and adjoining neural sites of the hypothalamus. A ligand-specific subunit of CNTF receptor complex (CNTFRα) has also been demonstrated expression in ARC and PVN.In this study we used radioimmunoassay-microdialysis procedure to measure the extracellular level of neuropeptide Y (NPY) in paraventricular nucleus (PVN) so that we could assess the effect of CNTF on secrete of NPY. The results showed NPY concentrations in PVN of freely moving rats rapidly decreased to the lowest point, 47% (P＜0.01) of basal level, in 30 minutes after intracerebroventricular injection 5μg CNTF, and then increased slowly to 58% (P＜0.05), 78% (P＜0.05) and 85% (P＜0.05) of basal level respectively at 60, 90 and 120 rain. It became no significant difference with basal level at 150 and 180 rain (P＞0.05). This result was the direct evidence to illustrate CNTF could decrease NPY peptide level in PVN of freely moving rats.In the present study, firstly, we found that CNTF elevated the expression of UCP1 in BAT and UCP3 in gastrocnemius muscle. Secondly, our data also showed that direct evidence to illustrate CNTF could decrease extracellular NPY level in hypothalamus. These were contributed for developing the mechanism of CNTF to lose weight.