Characterization of the high-affinity uptake of fructose-1,6-bisphosphate by cardiac myocytes

Fructose-2,6-bisphosphate restores DNA repair activity of PNKP and ameliorates neurodegenerative symptoms in Huntington's disease

Huntington's disease (HD) and spinocerebellar ataxia type 3 (SCA3) are the two most prevalent polyglutamine (polyQ) neurodegenerative diseases, caused by CAG (encoding glutamine) repeat expansion in the coding region of the huntingtin (HTT) and ataxin-3 (ATXN3) proteins, respectively. We have earlier reported that the activity, but not the protein level, of an essential DNA repair enzyme, polynucleotide kinase 3'-phosphatase (PNKP), is severely abrogated in both HD and SCA3 resulting in accumulation of double-strand breaks in patients' brain genome. While investigating the mechanistic basis for the loss of PNKP activity and accumulation of DNA double-strand breaks leading to neuronal death, we observed that PNKP interacts with the nuclear isoform of 6-phosphofructo-2-kinase fructose-2,6-bisphosphatase 3 (PFKFB3). Depletion of PFKFB3 markedly abrogates PNKP activity without changing its protein level. Notably, the levels of both PFKFB3 and its product fructose-2,6 bisphosphate (F2,6BP), an allosteric modulator of glycolysis, are significantly lower in the nuclear extracts of post-mortem brain tissues of HD and SCA3 patients. Supplementation of F2,6BP restored PNKP activity in the nuclear extracts of patients' brain. Moreover, intracellular delivery of F2,6BP restored both the activity of PNKP and the integrity of transcribed genome in neuronal cells derived from striatum of HD mouse. Importantly, supplementing F2,6BP rescued the HD phenotype in Drosophila, suggesting F2,6BP to serve in vivo as a cofactor for the proper functionality of PNKP and thereby, of brain health. Our results thus provide a compelling rationale for exploring the therapeutic use of F2,6BP and structurally related compounds for treating polyQ diseases.

Regulation of Glucose Metabolism for Cell Energy Supply In Situ via High-Energy Intermediate Fructose Hydrogels

The cellular functions, such as tissue-rebuilding ability, can be directly affected by the metabolism of cells. Moreover, the glucose metabolism is one of the most important processes of the metabolism. However, glucose cannot be efficiently converted into energy in cells under ischemia hypoxia conditions. In this study, a high-energy intermediate fructose hydrogel (HIFH) is developed by the dynamic coordination between sulfhydryl-functionalized bovine serum albumin (BSA-SH), the high-energy intermediate in glucose metabolism (fructose-1,6-bisphosphate, FBP), and copper ion (Cu2+). This hydrogel system is injectable, self-healing, and biocompatible, which can intracellularly convert energy with high efficacy by regulating the glucose metabolism in situ. Additionally, the HIFH can greatly boost cell antioxidant capacity and increase adenosine triphosphate (ATP) in the ischemia anoxic milieu by roughly 1.3 times, improving cell survival, proliferation and physiological functions in vitro. Furthermore, the ischemic skin tissue model is established in rats. The HIFH can speed up the healing of damaged tissue by promoting angiogenesis, lowering reactive oxygen species (ROS), and eventually expanding the healing area of the damaged tissue by roughly 1.4 times in vivo. Therefore, the HIFH can provide an impressive perspective on efficient in situ cell energy supply of damaged tissue.

Targeting a moonlighting function of aldolase induces apoptosis in cancer cells

Muscle fructose-1,6-bisphosphate aldolase (ALDOA) is among the most abundant glycolytic enzymes in all cancer cells. Here, we show that the enzyme plays a previously unknown and critical role in a cancer cell survival. Simultaneous inhibition of ALDOA activity and interaction with F-actin cytoskeleton using ALDOA slow-binding inhibitor UM0112176 leads to a rapid cofilin-dependent loss of F-actin stress fibers which is associated with elevated ROS production, inhibition of ATP synthesis, increase in calcium levels, caspase activation and arrested cellular proliferation. These effects can be reproduced by silencing of ALDOA. The mechanism of pharmacological action is, however, independent of the catalytic function of the enzyme, specific to cancer cells, and is most deleterious to cells undergoing the epithelial–mesenchymal transition, a process facilitating cancer cell invasion. Our results demonstrate that the overabundance of ALDOA in cancer cells is associated with its moonlighting rather than catalytic functions. This may have significant implications for development of novel broad-based anti-cancer therapies.

The Glycolytic Metabolite, Fructose-1,6-bisphosphate, Blocks Epileptiform Bursts by Attenuating Voltage-Activated Calcium Currents in Hippocampal Slices

Manipulation of metabolic pathways (e.g., ketogenic diet (KD), glycolytic inhibition) alters neural excitability and represents a novel strategy for treatment of drug-refractory seizures. We have previously shown that inhibition of glycolysis suppresses epileptiform activity in hippocampal slices. In the present study, we aimed to examine the role of a “branching” metabolic pathway stemming off glycolysis (i.e., the pentose-phosphate pathway, PPP) in regulating seizure activity, by using a potent PPP stimulator and glycolytic intermediate, fructose-1,6-bisphosphate (F1,6BP). Employing electrophysiological approaches, we investigated the action of F1,6BP on epileptiform population bursts, intrinsic neuronal firing, glutamatergic and GABAergic synaptic transmission and voltage-activated calcium currents (I_Ca) in the CA3 area of hippocampal slices. Bath application of F1,6BP (2.5–5 mM) blocked epileptiform population bursts induced in Mg²⁺-free medium containing 4-aminopyridine, in ~2/3 of the slices. The blockade occurred relatively rapidly (~4 min), suggesting an extracellular mechanism. However, F1,6BP did not block spontaneous intrinsic firing of the CA3 neurons (when synaptic transmission was eliminated with DNQX, AP-5 and SR95531), nor did it significantly reduce AMPA or NMDA receptor-mediated excitatory postsynaptic currents (EPSC_AMPA and EPSC_NMDA). In contrast, F1,6BP caused moderate reduction (~50%) in GABA_A receptor-mediated current, suggesting it affects excitatory and inhibitory synapses differently. Finally and unexpectedly, F1,6BP consistently attenuated I_Ca by ~40% without altering channel activation or inactivation kinetics, which may explain its anticonvulsant action, at least in this in vitro seizure model. Consistent with these results, epileptiform population bursts in CA3 were readily blocked by the nonspecific Ca²⁺ channel blocker, CdCl₂ (20 μM), suggesting that these bursts are calcium dependent. Altogether, these data demonstrate that the glycolytic metabolite, F1,6BP, blocks epileptiform activity via a previously unrecognized extracellular effect on I_Ca, which provides new insight into the metabolic control of neural excitability.