Nuclear Translocation of LDHA Promotes the Catabolism of BCAAs to Sustain GBM Cell Proliferation through the TxN Antioxidant Pathway.

Glutamate is excitotoxic to neurons. The entry of glutamine or glutamate from the blood into the brain is limited. To overcome this, branched-chain amino acids (BCAAs) catabolism replenishes the glutamate in brain cells. Branched-chain amino acid transaminase 1 (BCAT1) activity is silenced by epigenetic methylation in IDH mutant gliomas. However, glioblastomas (GBMs) express wild type IDH. Here, we investigated how oxidative stress promotes BCAAs' metabolism to maintain intracellular redox balance and, consequently, the rapid progression of GBMs. We found that reactive oxygen species (ROS) accumulation promoted the nuclear translocation of lactate dehydrogenase A (LDHA), which triggered DOT1L (disruptor of telomeric silencing 1-like)-mediated histone H3K79 hypermethylation and enhanced BCAA catabolism in GBM cells. Glutamate derived from BCAAs catabolism participates in antioxidant thioredoxin (TxN) production. The inhibition of BCAT1 decreased the tumorigenicity of GBM cells in orthotopically transplanted nude mice, and prolonged their survival time. In GBM samples, BCAT1 expression was negatively correlated with the overall survival time (OS) of patients. These findings highlight the role of the non-canonical enzyme activity of LDHA on BCAT1 expression, which links the two major metabolic pathways in GBMs. Glutamate produced by the catabolism of BCAAs was involved in complementary antioxidant TxN synthesis to balance the redox state in tumor cells and promote the progression of GBMs.

[Apoptosis and apoptosis-related genes in experimental autoimmune inner ear disease].

OBJECTIVE: To investigate the protein and mRNA expression patterns of apoptosis-related genes, together with evidence of apoptosis, in relation to experimental autoimmune inner ear disease (AIED). METHODS: Male C57BL/6 mice at 4 weeks age (n = 80) were randomly assigned to one of the five group (n = 16). The inbred mice were given a single subcutaneous injection of diluted solution of pertussis and an emulsion containing equal parts of complete Freund adjuvant (CFA) and inner ear antigens (IEAg) extracted form guinea pig. The animals were sacrificed for inner ear examination at a defined time after the immunization (7, 14, 21 or 28 days). An autoimmune inner ear diseases model was established. Apoptosis was detected by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (d-UTP) nick end-laying (TUNEL) method. Using immunohistochemical techniques and reverse transcriptase polymerase chain reaction to clarify the profile of Fas, FasL, and bcl-2. RESULTS: Under normal conditions, no TUNEL-positive cell was observed in the cochlea except for a few positive cells in the supporting cells of Corti's organ and macula sacculi. Inner ear antigens administration induced TUNEL-positive reactions in a wide variety of cells such as inner hair cells, supporting cells, stria vascularis and spiral ligament fibrocytes. No positive staining was evident in outer hair cells, spiral ganglion cells and Scarpa's ganglion cells during the whole period. Fas proteins were expressed in a wide range of cells in inner ear. The levels of Fas mRNA were no significant differences between normal and AIED mice. FasL and bcl-2 proteins could be detected in spiral ganglion cells and Scarpa's ganglion cells both in normal and AIED mice. FasL positive cells increased in number in inner ear of AIED mice. bcl-2 positive cells were not detectable in inner hair cells, stria vascularis and spiral ligament both in normal and AIED mice. The mRNA of three kinds of apoptosis-related genes was detectable in the normal and AIED mice. FasL mRNA was expressed at low levels in normal, being maximal at 14 d post inoculation and decreased gradually to steady levels by 2 weeks. The levels of bcl-2 mRNA increased significantly during the period of AIED. CONCLUSION: Apoptosis mediated by Fas/FasL signal system may play a role in the initiation and maintenance of AIED. bcl-2 has a crucial role in the regulation of the process of apoptosis in the inner ear of AIED mice.