Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism

Regulation of respiratory complex I assembly by FMN cofactor targeting

Respiratory complex I plays a crucial role in the mitochondrial electron transport chain and shows promise as a therapeutic target for various human diseases. While most studies focus on inhibiting complex I at the Q-site, little is known about inhibitors targeting other sites within the complex. In this study, we demonstrate that diphenyleneiodonium (DPI), a N-site inhibitor, uniquely affects the stability of complex I by reacting with its flavin cofactor FMN. Treatment with DPI blocks the final stage of complex I assembly, leading to the complete and reversible degradation of complex I in different cellular models. Growing cells in medium lacking the FMN precursor riboflavin or knocking out the mitochondrial flavin carrier gene SLC25A32 results in a similar complex I degradation. Overall, our findings establish a direct connection between mitochondrial flavin homeostasis and complex I stability and assembly, paving the way for novel pharmacological strategies to regulate respiratory complex I.

New insights into the nutritional genomics of adult-onset riboflavin-responsive diseases

Riboflavin, or vitamin B2, is an essential nutrient that serves as a precursor to flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). The binding of the FAD and/or FMN cofactors to flavoproteins is critical for regulating their assembly and activity. There are over 90 proteins in the human flavoproteome that regulate a diverse array of biochemical pathways including mitochondrial metabolism, riboflavin transport, ubiquinone and FAD synthesis, antioxidant signalling, one-carbon metabolism, nitric oxide signalling and peroxisome oxidative metabolism. The identification of patients with genetic variants in flavoprotein genes that lead to adult-onset pathologies remains a major diagnostic challenge. However, once identified, many patients with adult-onset inborn errors of metabolism demonstrate remarkable responses to riboflavin therapy. We review the structure:function relationships of mutant flavoproteins and propose new mechanistic insights into adult-onset riboflavin-responsive pathologies and metabolic dysregulations that apply to multiple biochemical pathways. We further address the vexing issue of how the inheritance of genetic variants in flavoprotein genes leads to an adult-onset disease with complex symptomologies and varying severities. We also propose a broad clinical framework that may not only improve the current diagnostic rates, but also facilitate a personalized approach to riboflavin therapy that is low cost, safe and lead to transformative outcomes in many patients.

SLC25A32 promotes malignant progression of glioblastoma by activating PI3K-AKT signaling pathway

BACKGROUND

Solute carrier family 25 member 32 (SLC25A32) is an important member of SLC25A family and plays a role in folate transport metabolism. However, the mechanism and function of SLC25A32 in the progression of human glioblastoma (GBM) remain unclear.

METHODS

In this study, folate related gene analysis was performed to explore gene expression profiles in low-grade glioma (LGG) and GBM. Western blotting, real-time quantitative PCR (qRT-PCR), and immunohistochemistry (IHC) were used to confirm the expression levels of SLC25A32 in GBM tissues and cell lines. CCK-8 assays, colony formation assays, and Edu assays were performed to assess the role of SLC25A32 on proliferation in GBM in vitro. A 3D sphere invasion assay and an ex vivo co-culture invasion model were performed to assess the effects of SLC25A32 on invasion in GBM.

RESULTS

Elevated expression of SLC25A32 was observed in GBM, and high SLC25A32 expression was associated with a high glioma grade and poorer prognosis. Immunohistochemistry performed with anti-SLC25A32 on samples from an independent cohort of patients confirmed these results. Knockdown of SLC25A32 inhibited the proliferation and invasion of GBM cells, but overexpression of SLC25A32 significantly promoted cell growth and invasion. These effects were mainly due to the activation of the PI3K-AKT-mTOR signaling pathway.

CONCLUSION

Our study demonstrated that SLC25A32 plays a significant role in promoting the malignant phenotype of GBM. Therefore, SLC25A32 can be used as an independent prognostic factor in patients with GBM, providing a new target for the comprehensive treatment of GBM.