Hexokinase 2‐dependent hyperglycolysis driving microglial activation contributes to ischemic brain injury

Abstract

Hyperglycolysis, observed within the penumbra zone during brain ischemia, was shown to be detrimental for tissue survival because of lactate accumulation and reactive oxygen species overproduction in clinical and experimental settings. Recently, mounting evidence suggests that glycolytic reprogramming and induced metabolic enzymes can fuel the activation of peripheral immune cells. However, the possible roles and details regarding hyperglycolysis in neuroinflammation during ischemia are relatively poorly understood. Here, we investigated whether overactivated glycolysis could activate microglia and identified the crucial regulators of neuroinflammatory responses in vitro and in vivo. Using BV 2 and primary microglial cultures, we found hyperglycolysis and induction of the key glycolytic enzyme hexokinase 2 (HK2) were essential for microglia-mediated neuroinflammation under hypoxia. Mechanistically, HK2 up-regulation led to accumulated acetyl-coenzyme A, which accounted for the subsequent histone acetylation and transcriptional activation of interleukin (IL)-1β. The inhibition and selective knockdown of HK2 in vivo significantly protected against ischemic brain injury by suppressing microglial activation and IL-1β production in male Sprague-Dawley rats subjected to transient middle cerebral artery occlusion (MCAo) surgery. We provide novel insights for HK2 specifically serving as a neuroinflammatory determinant, thus explaining the neurotoxic effect of hyperglycolysis and indicating the possibility of selectively targeting HK2 as a therapeutic strategy in acute ischemic stroke.

Metabolic Reprogramming during Microglia Activation

“…Additionally, in our study, for the first time, we demonstrated that not only murine, but also human microglia-like cells exhibit increased glycolysis in a pro-inflammatory setting, implying glycolysis as an M1 microglia feature. Importantly, several studies have already demonstrated that inhibition of glycolysis in microglia can prevent pro-inflammatory microglia activation both in vitro and in vivo, further supporting this notion [31,59,60]. For example, treatment of microglia with 2-deoxyglucose, a glycolytic inhibitor, is able to diminish the NO production in LPS-treated microglia, which could be useful for inhibiting neurotoxic microglia properties [59].…”

“…For example, treatment of microglia with 2-deoxyglucose, a glycolytic inhibitor, is able to diminish the NO production in LPS-treated microglia, which could be useful for inhibiting neurotoxic microglia properties [59]. Moreover, several studies have reported beneficial effects of 2-deoxyglucose in Alzheimer's disease (AD) [34], Parkinson's disease [35], epilepsy [36] and ischemic stroke [31]. However, all these studies involved systemic, nonmicroglia specific treatments, so the effect of such approaches could not be assigned directly or solely to microglia.…”

“…We clearly demonstrated that the most pronounced metabolic adaptation in pro-inflammatory microglia is the increase in glycolysis. Interestingly, several studies in rodents highlighted beneficial effects of suppressing glycolysis on the outcome of events such as stroke [31]. In order to potentially translate this to patients, an outstanding question is whether pro-inflammatory human microglia display similar metabolic adaptations.…”

“…In parallel, LPS-activated microglia exhibit decreased mitochondrial function evidenced by the reduction in the activity of respiratory chain enzymes and the reduction in mitochondrial OXPHOS [22,23,28,29]. However, despite the fact that metabolic alterations in microglia have been implicated in several disease models and in aging [25,[30][31][32][33], it remains largely unknown how most pathways are regulated. Moreover, metabolic approaches have already been applied in several CNS pathologies and had positive effects, although the cellular target was not defined [31,[34][35][36][37].…”

Hexokinase-2 Glycolytic Overload in Diabetes and Ischemia–Reperfusion Injury

“…HIF1 and related hypoxia-activated HIF2, however, also induce expression and activity of downstream glycolytic enzymes -PFK-muscle type (PFK-M), regulatory enzymes 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 and -4, aldolase, triosephosphate isomerase (TPI), and GA3PD [38]. This suggests that, unlike in glycolytic overload where only HK2 activity is increased, in hypoxia the flux of glucose metabolism may increase without an increase in G6P and other glycolytic intermediates because of a coordinated increased onward rate of metabolism of glycolytic intermediates [41,42]. A remaining potentially insidious effect, however, is the down regulation of glyoxalase (Glo)1 in hypoxia [43,44] the major enzyme that metabolizes and detoxifies MG [45].…”