Abstract
Lactic acidosis, glucose deprivation and hypoxia are conditions frequently found in solid tumors because, among other reasons, tumors switch to Warburg effect and secrete high levels of lactate, which decreases the pH (<6. 9) in the microenvironment. We hypothesized that lung cancer cells consume lactate and induce mitochondrial biogenesis to support survival and proliferation in lactic acidosis with glucose deprivation even under hypoxia. We examined lung adenocarcinoma cell lines (A-427 and A-549), a breast cancer cell line (MCF-7) and non-transformed fibroblasts (MRC-5). Cells were cultured using RPMI-1640 medium with 28 mM lactate varying pH (6.2 or 7.2) under normoxia (atmospheric O2) or hypoxia (2% O2). Cellular growth was followed during 96 h, as well as lactate, glutamine and glutamate levels, which were measured using a biochemical analyzer. The expression levels of monocarboxylate transporters (MCT1 and MCT4) were evaluated by flow cytometry. To evaluate mitochondrial biogenesis, mitochondrial mass was analyzed by flow cytometry and epifluorescence microscopy. Also, mitochondrial DNA (mtDNA) was measured by qPCR. Transcript levels of Nuclear Respiratory Factors (NRF-1 and NRF-2) and Transcription Factor A Mitochondrial (TFAM) were determined using RT-qPCR. The specific growth rate of A-549 and A-427 cells increased in lactic acidosis compared with neutral lactosis, either under normoxia or hypoxia, a phenomenon that was not observed in MRC-5 fibroblasts. Under hypoxia, A-427 and MCF-7 cells did not survive in neutral lactosis but survived in lactic acidosis. Under lactic acidosis, A-427 and MCF-7 cells increased MCT1 levels, reduced MCT4 levels and consumed higher lactate amounts, while A-549 cells consumed glutamine and decreased MCT1 and MCT4 levels with respect to neutral lactosis condition. Lactic acidosis, either under normoxia or hypoxia, increased mitochondrial mass and mtDNA levels compared with neutral lactosis in all tumor cells but not in fibroblasts. A-549 and MCF-7 cells increased levels of NRF-1, NRF-2, and TFAM with respect to MRC-5 cells, whereas A-427 cells upregulated these transcripts under lactic acidosis compared with neutral lactosis. Thus, lung adenocarcinoma cells induce mitochondrial biogenesis to support survival and proliferation in lactic acidosis with glucose deprivation.
Highlights
Lactic acidosis is a common condition found in solid tumors [1,2,3]; for instance, in breast cancer patients, intratumoral lactate levels range from 0.6 to 8.0 μmol/g [4]
We found that the specific growth rate (μ) of A-549 and A-427 cells significantly increased under lactic acidosis compared with neutral lactosis either under normoxia or hypoxia
A-427 and MCF7 tumor cells did not survive in neutral lactosis under hypoxia and they showed a decline in proliferation associated with cell death, because the cell number at 48 h was smaller than time zero (Figure 1)
Summary
Lactic acidosis is a common condition found in solid tumors [1,2,3]; for instance, in breast cancer patients, intratumoral lactate levels range from 0.6 to 8.0 μmol/g [4]. Because the tumor microenvironment is variable, cells that initially had access to high glucose levels and normal oxygen concentrations may eventually encounter an environment with lactic acidosis [1, 7], absence of glucose [1] and hypoxia [8]. The tumor mass has an estimated median PO2 value of 10 mmHg (1.5% O2), whereas in normal breast tissue, it is 65 mmHg [8]. These changes in the microenvironment might favor tumor survival and invasion; in this regard, hypoxia is known to favor angiogenesis, metastasis, and resistance to radiation and chemotherapies [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
