Testosterone upregulates glial cell line-derived neurotrophic factor (GDNF) and promotes neuroinflammation to enhance glioma cell survival and proliferation

BACKGROUND

Testosterone contributes to male organism development, such as bone density, muscle development, and fat repartition. Estrogen (derived from testosterone) also contributes to female reproductive system development. Here, we investigated the effect of testosterone on glioma cells and brain neuron inflammation essential for cancer development and progression.

METHODS

The human astrocyte and glioma cell lines were treated with 6 ng/ml exogenous testosterone in vitro. We performed cell counting kit-8, transwell, and wound healing assays to determine the effect of testosterone on glioma cell proliferation, migration, and invasion. The glioma cells were injected into the xenograft and treated with 5 µl concentrated testosterone. Transcriptional suppression of glial cell line-derived neurotrophic factor (GDNF) was performed to evaluate brain neuron inflammation and survival. The tumor tissues were assessed by hematoxylin-eosin staining and immunohistochemistry.

RESULTS

Testosterone upregulates GDNF to stimulate proliferation, migration, and invasion of glioma cells. Pathologically, the augmentation of GDNF and cyclophilin A contributed to neuroprotection when treated with testosterone. Our investigation showed that testosterone contributes to brain neuron and astrocyte inflammation through the upregulation of nuclear factor erythroid 2-related factor 2 (NRF2), glial fibrillary acid protein (GFAP), and sirtuin 5 (SIRT5), resulting in pro-inflammatory macrophages recruitments into the neural microenvironment. Mechanically, testosterone treatment regulates GDNF translocation from the glioma cells and astrocyte nuclei to the cytoplasm.

CONCLUSION

Testosterone upregulates GDNF in glioma cells and astrocytes essential for microglial proliferation, migration, and invasion. Testosterone contributes to brain tumor growth via GDNF and inflammation. The contribution of testosterone, macrophages, and astrocytes, in old neuron rescue, survival, and proliferation. During brain neuron inflammation, the organism activates and stimulates the neuron rescue through the enrichment of the old neuron microenvironment with growth factors such as GDNF, BDNF, SOX1/2, and MAPK secreted by the surrounding neurons and glial cells to maintain the damaged neuron by inflammation alive even if the axon is dead. The immune response also contributes to brain cell survival through the secretion of proinflammatory cytokines, resulting in inflammation maintenance. The rescued old neuron interaction with infiltrated macrophages contributes to angiogenesis to supplement the old neuron with more nutrients leading to metabolism activation and surrounding cell uncontrollable cell growth.

Cancer Metabolism: The Role of Immune Cells Epigenetic Alteration in Tumorigenesis, Progression, and Metastasis of Glioma

Glioma is a type of brain and spinal cord tumor that begins in glial cells that support the nervous system neurons functions. Age, radiation exposure, and family background of glioma constitute are risk factors of glioma initiation. Gliomas are categorized on a scale of four grades according to their growth rate. Grades one and two grow slowly, while grades three and four grow faster. Glioblastoma is a grade four gliomas and the deadliest due to its aggressive nature (accelerated proliferation, invasion, and migration). As such, multiple therapeutic approaches are required to improve treatment outcomes. Recently, studies have implicated the significant roles of immune cells in tumorigenesis and the progression of glioma. The energy demands of gliomas alter their microenvironment quality, thereby inducing heterogeneity and plasticity change of stromal and immune cells via the PI3K/AKT/mTOR pathway, which ultimately results in epigenetic modifications that facilitates tumor growth. PI3K is utilized by many intracellular signaling pathways ensuring the proper functioning of the cell. The activation of PI3K/AKT/mTOR regulates the plasma membrane activities, contributing to the phosphorylation reaction necessary for transcription factors activities and oncogenes hyperactivation. The pleiotropic nature of PI3K/AKT/mTOR makes its activity unpredictable during altered cellular functions. Modification of cancer cell microenvironment affects many cell types, including immune cells that are the frontline cells involved in inflammatory cascades caused by cancer cells via high cytokines synthesis. Typically, the evasion of immunosurveillance by gliomas and their resistance to treatment has been attributed to epigenetic reprogramming of immune cells in the tumor microenvironment, which results from cancer metabolism. Hence, it is speculative that impeding cancer metabolism and/or circumventing the epigenetic alteration of immune cell functions in the tumor microenvironment might enhance treatment outcomes. Herein, from an oncological and immunological perspective, this review discusses the underlying pathomechanism of cell-cell interactions enhancing glioma initiation and metabolism activation and tumor microenvironment changes that affect epigenetic modifications in immune cells. Finally, prospects for therapeutic intervention were highlighted.

Extracellular and Intracellular Factors in Brain Cancer

The external and internal factors of the cell are critical to glioma initiation. Several factors and molecules have been reported to be implicated in the initiation and progression of brain cancer. However, the exact sequence of events responsible for glioma initiation is still unknown. Existing reports indicate that glioma stem cells are the cell of glioma origin. During cell division, chromosome breakage, DNA alteration increases the chance of cell genome modifications and oncogene overexpression. Although there is a high risk of gene alteration and oncogene overexpression, not everyone develops cancer. During embryogenesis, the same oncogenes that promote cancers have also been reported to be highly expressed, but this high expression which does not lead to carcinogenesis raises questions about the role of oncogenes in carcinogenesis. The resistance of cancer cells to drugs, apoptosis, and immune cells does not rely solely on oncogene overexpression but also on the defect in cell organelle machinery (mitochondria, endoplasmic reticulum, and cytoskeleton). This review discusses factors contributing to cancer; we report the dysfunction of the cell organelles and their contribution to carcinogenesis, while oncogene overexpression promotes tumorigenesis, maintenance, and progression through cell adhesion. All these factors together represent a fundamental requirement for cancer and its development.