Korean Red Ginseng-Induced SIRT3 Promotes the Tom22-HIF-1α Circuit in Normoxic Astrocytes.

Astrocytes play a key role in brain functioning by providing energy to neurons. Increased astrocytic mitochondrial functions by Korean red ginseng extract (KRGE) have been investigated in previous studies. KRGE administration induces hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in astrocytes in the adult mouse brain cortex. VEGF expression can be controlled by transcription factors, such as the HIF-1α and estrogen-related receptor α (ERRα). However, the expression of ERRα is unchanged by KRGE in astrocytes of the mouse brain cortex. Instead, sirtuin 3 (SIRT3) expression is induced by KRGE in astrocytes. SIRT3 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that resides in the mitochondria and maintains mitochondrial homeostasis. Mitochondrial maintenance requires oxygen, and active mitochondria enhance oxygen consumption, resulting in hypoxia. The effects of SIRT3 on HIF-1α-mediated mitochondria functions induced by KRGE are not well established. We aimed to investigate the relationship between SIRT3 and HIF-1α in KRGE-treated normoxic astrocyte cells. Without changing the expression of the ERRα, small interfering ribonucleic acid targeted for SIRT3 in astrocytes substantially lowers the amount of KRGE-induced HIF-1α proteins. Reduced proline hydroxylase 2 (PHD2) expression restores HIF-1α protein levels in SIRT3-depleted astrocytes in normoxic cells treated with KRGE. The translocation of outer mitochondrial membranes 22 (Tom22) and Tom20 is controlled by the SIRT3-HIF-1α axis, which is activated by KRGE. KRGE-induced Tom22 increased oxygen consumption and mitochondrial membrane potential, as well as HIF-1α stability through PHD2. Taken together, in normoxic astrocytes, KRGE-induced SIRT3 activated the Tom22-HIF-1α circuit by increasing oxygen consumption in an ERRα-independent manner.

Induction of BVR-A Expression by Korean Red Ginseng in Murine Hippocampal Astrocytes: Role of Bilirubin in Mitochondrial Function via the LKB1-SIRT1-ERRα Axis.

The beneficial effects of Korean red ginseng extract (KRGE) on the central nervous system (CNS) have been reported. Among the CNS cells, astrocytes possess robust antioxidative properties and regenerative potential. Under physiological conditions, biliverdin reductase A (BVR-A) converts biliverdin (a heme oxygenase metabolite) into bilirubin, a major natural and potent antioxidant. We found that KRGE enhanced BVR-A in astrocytes in the fimbria region of the adult mouse hippocampus under physiological conditions. KRGE-induced BVR-A expression and subsequent bilirubin production were required for changes in mitochondrial membrane potential, mitochondrial mass, and oxidative phosphorylation through liver kinase B1 (LKB1), estrogen-related receptor α (ERRα), and sirtuin (SIRT1 and SIRT5) in astrocytes. However, BVR-A did not affect the KRGE-induced expression of AMP-activated protein kinase α (AMPKα). The KRGE-stimulated BVR-A-LKB1-SIRT1-ERRα pathway regulates the levels of mitochondria-localized proteins such as SIRT5, translocase of the outer mitochondrial membrane 20 (Tom20), Tom22, cytochrome c (Cyt c), and superoxide dismutase 2 (SOD2). Increased Tom20 expression in astrocytes of the hippocampal fimbria region was observed in KRGE-treated mice. KRGE-induced expression of Cyt c and SOD2 was associated with the Tom20/Tom22 complex. Taken together, KRGE-induced bilirubin production is required for enhanced astrocytic mitochondrial function in an LKB1-dependent and AMPKα-independent manner under physiological conditions.

Prophylactic role of Korean Red Ginseng in astrocytic mitochondrial biogenesis through HIF-1α.

Background: Korean Red Ginseng extract (KRGE) has been used as a health supplement and herbal medicine. Astrocytes are one of the key cells in the central nervous system (CNS) and have bioenergetic potential as they stimulate mitochondrial biogenesis. They play a critical role in connecting the brain vasculature and nerves in the CNS. Methods: Brain samples from KRGE-administered mice were tested using immunohistochemistry. Treatment of human brain astrocytes with KRGE was subjected to assays such as proliferation, cytotoxicity, Mitotracker, ATP production, and O2 consumption rate as well as western blotting to demonstrate the expression of proteins related to mitochondria functions. The expression of hypoxia-inducible factor-1α (HIF-1α) was diminished utilizing siRNA transfection. Results: Brain samples from KRGE-administered mice harbored an increased number of GFAP-expressing astrocytes. KRGE triggered the proliferation of astrocytes in vitro. Enhanced mitochondrial biogenesis induced by KRGE was detected using Mitotracker staining, ATP production, and O2 consumption rate assays. The expression of proteins related to mitochondrial electron transport was increased in KRGE-treated astrocytes. These effects were blocked by HIF-1α knockdown. The factors secreted from KRGE-treated astrocytes were determined, revealing the expression of various cytokines and growth factors, especially those related to angiogenesis and neurogenesis. KRGE-treated astrocyte conditioned media enhanced the differentiation of adult neural stem cells into mature neurons, increasing the migration of endothelial cells, and these effects were reduced in the background of HIF-1α knockdown. Conclusion: Our findings suggest that KRGE exhibits prophylactic potential by stimulating astrocyte mitochondrial biogenesis through HIF-1α, resulting in improved neurovascular function.

Dual Effects of Korean Red Ginseng on Astrocytes and Neural Stem Cells in Traumatic Brain Injury: The HO-1-Tom20 Axis as a Putative Target for Mitochondrial Function.

Astrocytes display regenerative potential in pathophysiologic conditions. In our previous study, heme oxygenase-1 (HO-1) promoted astrocytic mitochondrial functions in mice via the peroxisome-proliferator-activating receptor-γ coactivator-1α (PGC-1α) pathway on administering Korean red ginseng extract (KRGE) after traumatic brain injury (TBI). In this study, KRGE promoted astrocytic mitochondrial functions, assessed with oxygen consumption and adenosine triphosphate (ATP) production, which could be regulated by the translocase of the outer membrane of mitochondria 20 (Tom20) pathway with a PGC-1α-independent pathway. The HO-1-Tom20 axis induced an increase in mitochondrial functions, detected with cytochrome c oxidase subunit 2 and cytochrome c. HO-1 crosstalk with nicotinamide phosphoribosyltransferase was concomitant with the upregulated nicotinamide adenine dinucleotide (NAD)/NADH ratio, thereby upregulating NAD-dependent class I sirtuins. In adult neural stem cells (NSCs), KRGE-treated, astrocyte-conditioned media increased oxygen consumption and Tom20 levels through astrocyte-derived HO-1. HO inactivation by Sn(IV) protoporphyrin IX dichloride in TBI mice administered KRGE decreased neuronal markers, together with Tom20. Thus, astrocytic HO-1 induced astrocytic mitochondrial functions. HO-1-related, astrocyte-derived factors may also induce neuronal differentiation and mitochondrial functions of adult NSCs after TBI. KRGE-mediated astrocytic HO-1 induction may have a key role in repairing neurovascular function post-TBI in peri-injured regions by boosting astrocytic and NSC mitochondrial functions.

Korean Red Ginseng Improves Astrocytic Mitochondrial Function by Upregulating HO-1-Mediated AMPKα-PGC-1α-ERRα Circuit after Traumatic Brain Injury.

Heme oxygenase-1 (HO-1) exerts beneficial effects, including angiogenesis and energy metabolism via the peroxisome proliferator-activating receptor-γ coactivator-1α (PGC-1α)-estrogen-related receptor α (ERRα) pathway in astrocytes. However, the role of Korean red ginseng extract (KRGE) in HO-1-mediated mitochondrial function in traumatic brain injury (TBI) is not well-elucidated. We found that HO-1 was upregulated in astrocytes located in peri-injured brain regions after a TBI, following exposure to KRGE. Experiments with pharmacological inhibitors and target-specific siRNAs revealed that HO-1 levels highly correlated with increased AMP-activated protein kinase α (AMPKα) activation, which led to the PGC-1α-ERRα axis-induced increases in mitochondrial functions (detected based on expression of cytochrome c oxidase subunit 2 (MTCO2) and cytochrome c as well as O2 consumption and ATP production). Knockdown of ERRα significantly reduced the p-AMPKα/AMPKα ratio and PGC-1α expression, leading to AMPKα-PGC-1α-ERRα circuit formation. Inactivation of HO by injecting the HO inhibitor Sn(IV) protoporphyrin IX dichloride diminished the expression of p-AMPKα, PGC-1α, ERRα, MTCO2, and cytochrome c in the KRGE-administered peri-injured region of a brain subjected to TBI. These data suggest that KRGE enhanced astrocytic mitochondrial function via a HO-1-mediated AMPKα-PGC-1α-ERRα circuit and consequent oxidative phosphorylation, O2 consumption, and ATP production. This circuit may play an important role in repairing neurovascular function after TBI in the peri-injured region by stimulating astrocytic mitochondrial biogenesis.

Repair Mechanisms of the Neurovascular Unit after Ischemic Stroke with a Focus on VEGF.

The functional neural circuits are partially repaired after an ischemic stroke in the central nervous system (CNS). In the CNS, neurovascular units, including neurons, endothelial cells, astrocytes, pericytes, microglia, and oligodendrocytes maintain homeostasis; however, these cellular networks are damaged after an ischemic stroke. The present review discusses the repair potential of stem cells (i.e., mesenchymal stem cells, endothelial precursor cells, and neural stem cells) and gaseous molecules (i.e., nitric oxide and carbon monoxide) with respect to neuroprotection in the acute phase and regeneration in the late phase after an ischemic stroke. Commonly shared molecular mechanisms in the neurovascular unit are associated with the vascular endothelial growth factor (VEGF) and its related factors. Stem cells and gaseous molecules may exert therapeutic effects by diminishing VEGF-mediated vascular leakage and facilitating VEGF-mediated regenerative capacity. This review presents an in-depth discussion of the regeneration ability by which endogenous neural stem cells and endothelial cells produce neurons and vessels capable of replacing injured neurons and vessels in the CNS.