Detection of the Uncoupling Protein (A Nucleotide-Modulated H+- Translocator) and its mRNA in Human Diseases

Abstract

The mitochondrial inner membrane contains several transport systems for metabolites. Among them there is the Uncoupling Protein (UCP), which is a 33KDa protein whose activity is inhibited by purine nucleotides (GDP, GTP, ADP and ATP) and is stimulated by free fatty acids following stimulation of cells by Norepinephrine in rodents. UCP is a H+ translocator which allows the regulated uncoupling of respiration and is uniquely expressed in a specialised adipose tissue, the brown adipose tissue (BAT). Since BAT is a thermogenic organ in rodents and UCP dissipates the gradient generated by the respiratory chain, the presence of UCP in the inner membrane of brown adipocyte mitochondria might account for BAT thermogenic capacity. Human UCP whose primary structure has already been determined by gene sequencing was recently detected in perirenal adipose deposits of human subjects with Pheochromocytoma (Pheo), a catecholamine-secreting tumor; thus, it was argued that catecholamines might play a crucial role in the expression of UCP in humans as well as in rodents. Furthermore, a high prevalence of BAT seems to be associated with cancer-induced cachexia and increased BAT activity has been found in some malignant diseases. However, no identification of UCP and its mRNA was performed in the last two studies. Hence, we investigated whether UCP and its mRNA are detectable in adipose deposits of adults with pathological conditions distinct from Pheo, with or without malignant diseases. In parallel assays we studied a group of subject with malignant or non-malignant Pheochromocytoma. All patients with Neoplasms did not show any sign of cancer-induced cachexia. By utilizing Western and Northern blotting we confirm that UCP and its mRNA are detectable in subjects with Pheo. However we also demonstrated the presence of human UCP in fat deposits of people with both endocrine and non-endocrine diseases distinct from Pheo, either in presence or in absence of malignancy.