Bioénergétique des tumeurs : impact de l'hypoxie et de l'aglycémie sur le métabolisme énergétique du cancer du sein

Abstract

Non-canonical bioenergetics concerns with those physiological and pathophysiological situations under which ATP synthesis is suppressed. This thesis brings an outcome of three types of studies within the field of the non-canonical bioenergetics, investigating specific bioenergetic phenotypes of cancer cells, on one hand; and a role of mitochondrial uncoupling proteins as deduced from their transcript distribution in various tissues and organs; plus a role of a novel and likely pro-apoptotic factor CIDEa in mitochondria. Cancer cells generally present abnormal bioenergetic properties including an elevated glucose uptake, a high glycolysis and a poorly efficient oxidative phosphorylation system. However, the determinants of cancer cells metabolic reprogramming remain unknown. The main question in this project was how environmental conditions in vivo can influence functioning of mitochondrial OXPHOS, because details of mitochondrial bioenergetics of cancer cells is poorly documented. We have combined two conditions, namely glucose and oxygen deprivation, to measure their potential interaction. We examined the impact of glucose deprivation and oxygen deprivation on cell survival, overall bioenergetics and OXPHOS protein expression. As a model, we have chosen a human breast carcinoma (HTB-126) and appropriate control (HTB-125) cultured cells, as large fraction of breast malignancies exhibit hypoxic tumor regions with low oxygen concentrations and poor glucose delivery. The results demonstrate that glucose presence or absence largely influence functioning of mitochochondrial oxidative phosphorylation. The level of mitochondrial respiration capacity is regulated by glucose; by Crabtree effect, by energy substrate channeling towards anabolic pathways that support cell growth and by mitochondrial biogenesis pathways. Both oxygen deprivation and glucose deprivation can remodel the OXPHOS system, albeit in opposite directions. As an adaptative response to hypoxia, glucose inhibits mitochondrial oxidative phosphorylation to the larger extent than in normoxia. We concluded that the energy profile of cancer cells can be determined by specific balance between two main environmental stresses, glucose and oxygen deprivation. Thus, variability of intratumoral environment might explain the variability of cancer cells´ bioenergetic profile. Mitochondrial uncoupling proteins are proteins of inner mitochondrial membrane that uncouple respiration from ATP synthesis by their protonophoric activity. Originally determined tissue distribution seems to be invalid, since novel findings show that UCP1 is not restricted exclusively to brown fat and that originally considered brain-specific isoforms UCP4 and UCP5 might have wider tissue distribution. Hence, in second part of this thesis, I discuss consequences of findings of UCPn transcripts in the studied mouse and rat tissues. We have shown that mRNA of UCPn varies up to four orders of magnitude in rat and mouse tissues with highest expression in rat spleen, rat and mouse lung, and rat heart. Levels of the same order of magnitude were found for UCP3 mRNA in rat 100 and mouse skeletal muscle, for UCP4 and UCP5 mRNA in mouse brain, and for UCP2 and UCP5 mRNA in mouse white adipose tissue. Further, we have shown that expression pattern of UCPn varies between animal species, rat versus mouse, such as the dominance of UCP3/UCP5 vs. UCP2 transcript in mouse heart and vice versa in rat heart; or UCP2 (UCP5) dominance in rat brain contrary to 10-fold higher UCP4 and UCP5 dominance in mouse brain. spontaneous apoptosis due to CIDEa overexpression in HeLa cells, adapted for a tetracycline-inducible CIDEa expression, a portion of mitochondria-localized CIDEa molecules migrates to cytosol or nucleus.