1,25-Dihydroxyvitamin D Regulation of Glutamine Synthetase and Glutamine Metabolism in Human Mammary Epithelial Cells

The role of vitamin D on redox regulation and cellular senescence

Vitamin D is considered an essential micronutrient for human health that is metabolized into a multifunctional secosteroid hormone. We can synthesize it in the skin through ultraviolet B (UVB) rays or acquire it from the diet. Its deficiency is a major global health problem that affects all ages and ethnic groups. Furthermore, dysregulation of vitamin D homeostasis has been associated with premature aging, driven by various cellular processes, including oxidative stress and cellular senescence. Various studies have shown that vitamin D can attenuate oxidative stress and delay cellular senescence, mainly by inducing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Klotho and improving mitochondrial homeostasis, proposing this vitamin as an excellent candidate for delaying aging. However, the mechanisms around these processes are not yet fully explored. Therefore, in this review, the effects of vitamin D on redox regulation and cellular senescence are discussed to propose new lines of research and clinical applications of vitamin D in the context of age-related diseases.

Vitamin D and Breast Cancer: Mechanistic Update

The presence of the vitamin D receptor (VDR) in mammary gland and breast cancer has long been recognized, and multiple preclinical studies have demonstrated that its ligand, 1,25-dihydroxyvitamin D (1,25D), modulates normal mammary gland development and inhibits growth of breast tumors in animal models. Vitamin D deficiency is common in breast cancer patients, and some evidence suggests that low vitamin D status enhances the risk for disease development or progression. Although many 1,25D-responsive targets in normal mammary cells and in breast cancers have been identified, validation of specific targets that regulate cell cycle, apoptosis, autophagy, and differentiation, particularly in vivo, has been challenging. Model systems of carcinogenesis have provided evidence that both VDR expression and 1,25D actions change with transformation, but clinical data regarding vitamin D responsiveness of established tumors is limited and inconclusive. Because breast cancer is heterogeneous, the relevant VDR targets and potential sensitivity to vitamin D repletion or supplementation will likely differ between patient populations. Detailed analysis of VDR actions in specific molecular subtypes of the disease will be necessary to clarify the conflicting data. Genomic, proteomic, and metabolomic analyses of in vitro and in vivo model systems are also warranted to comprehensively understand the network of vitamin D-regulated pathways in the context of breast cancer heterogeneity. This review provides an update on recent studies spanning the spectrum of mechanistic (cell/molecular), preclinical (animal models), and translational work on the role of vitamin D in breast cancer. © 2021 The Author. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

miR-190a-5p regulates cardiomyocytes response to ferroptosis via directly targeting GLS2

Ferroptosis is a novel identified form of regulated cell death that has been implied in the pathology of myocardial infarction (MI). However, the regulation mechanisms of ferroptosis in cardiomyocyte are still elusive. MiRNAs are a group of small non-coding RNAs that play crucial roles in various biological activities. Till now, little is known about the role of miRNA in the ferroptosis of cardiomyocytes. In the current study, we found that miR-190a-5p negatively regulate ferroptosis via directly targeting GLS2 in rat cardiomyocyte H9c2 cells. Forced expression of miR-190a-5p inhibited GLS2, resulting in downregulation of ROS, MDA and Fe ²⁺ accumulation. Meanwhile, inhibition of miR-190a-5p caused upregulation of GLS2, resulting in opposite effects which could be blocked by GLS2 inhibitor compound 968. In summary, our findings suggest that miR-190a-5p plays an essential role in regulation of ferroptosis of cardiomyocytes and suggest a potential therapeutic target for MI.

Vitamin D regulation of energy metabolism in cancer

Vitamin D exerts anti-cancer effects in recent clinical trials and preclinical models. The actions of vitamin D are primarily mediated through its hormonal form, 1,25-dihydroxyvitamin D (1,25(OH)₂ D). Previous literature describing in vitro studies has predominantly focused on the anti-tumourigenic effects of the hormone, such as proliferation and apoptosis. However, recent evidence has identified 1,25(OH)₂ D as a regulator of energy metabolism in cancer cells, where requirements for specific energy sources at different stages of progression are dramatically altered. The literature suggests that 1,25(OH)₂ D regulates energy metabolism, including glucose, glutamine and lipid metabolism during cancer progression, as well as oxidative stress protection, as it is closely associated with energy metabolism. Mechanisms involved in energy metabolism regulation are an emerging area in which vitamin D may inhibit multiple stages of cancer progression.

Vitamin D regulation of HAS2, hyaluronan synthesis and metabolism in triple negative breast cancer cells

The vitamin D receptor (VDR) and its ligand 1,25(OH)₂D₃ (1,25D) exert anti-tumor effects, but considerable heterogeneity has been reported in different model systems. In general, cell lines derived from aggressive tumor subtypes such as Triple Negative Breast Cancer (TNBC) express low levels of VDR and are less sensitive to 1,25D than those derived from more differentiated tumor types. We have previously reported that 1,25D inhibits hyaluronic acid synthase 2 (HAS2) expression and hyaluronic acid (HA) synthesis in murine TNBC cells. Here we confirmed the inhibitory effect of 1,25D on HA synthesis in human Hs578T cells representative of the mesenchymal/stem-like (MSL) subtype of TNBC. Because HA synthesis requires the production of hexoses for incorporation into HA, we predicted that the high HA production characteristic of Hs578T cells would require sustained metabolic changes through the hexosamine biosynthetic pathway (HBP). We thus examined metabolic gene expression in Hs578T cell variants sorted for High (HA^High) and Low (HA^Low) HA production, and the ability of 1,25D to reverse these adaptive changes. HA^High populations exhibited elevated HA production, smaller size, increased proliferation and higher motility than HA^Low populations. Despite their more aggressive phenotype, HA^High populations retained expression of VDR protein at levels comparable to that of parental Hs578T cells and HA^Low subclones. Treatment with 1,25D decreased production of HA in both HA^High and HA^Low populations. We also found that multiple metabolic enzymes were aberrantly expressed in HA^High cells, especially those involved in glutamine and glucose metabolism. Notably, Glutaminase (GLS), a known oncogene for breast cancer, was strongly upregulated in HA^High vs. HA^Low cells and its expression was significantly reduced by 1,25D (100 nM, 24 h). Consistent with this finding, Seahorse extracellular flux analysis indicated that respiration in HA^High cells was significantly more dependent on exogenous glutamine than HA^Low cells, however, acute 1,25D exposure did not alter metabolic flux. In contrast to GLS, the glutamate transporter SLC1A7 was significantly reduced in HA^High cells compared to HA^Low cells and its expression was enhanced by 1,25D. These findings support the concept that 1,25D can reverse the metabolic gene expression changes associated with HA production in cancer cells with aggressive phenotypes.