Creatine transporter deficiency impairs stress adaptation and brain energetics homeostasis

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

Dodecyl creatine ester therapy: from promise to reality

Pathogenic variants in SLC6A8, the gene which encodes creatine transporter SLC6A8, prevent creatine uptake in the brain and result in a variable degree of intellectual disability, behavioral disorders (e.g., autism spectrum disorder), epilepsy, and severe speech and language delay. There are no treatments to improve neurodevelopmental outcomes for creatine transporter deficiency (CTD). In this spotlight, we summarize recent advances in innovative molecules to treat CTD, with a focus on dodecyl creatine ester, the most promising drug candidate.

Deciphering neuronal deficit and protein profile changes in human brain organoids from patients with creatine transporter deficiency

Creatine transporter deficiency (CTD) is an X-linked disease caused by mutations in the SLC6A8 gene. The impaired creatine uptake in the brain results in intellectual disability, behavioral disorders, language delay, and seizures. In this work, we generated human brain organoids from induced pluripotent stem cells of healthy subjects and CTD patients. Brain organoids from CTD donors had reduced creatine uptake compared with those from healthy donors. The expression of neural progenitor cell markers SOX2 and PAX6 was reduced in CTD-derived organoids, while GSK3β, a key regulator of neurogenesis, was up-regulated. Shotgun proteomics combined with integrative bioinformatic and statistical analysis identified changes in the abundance of proteins associated with intellectual disability, epilepsy, and autism. Re-establishment of the expression of a functional SLC6A8 in CTD-derived organoids restored creatine uptake and normalized the expression of SOX2, GSK3β, and other key proteins associated with clinical features of CTD patients. Our brain organoid model opens new avenues for further characterizing the CTD pathophysiology and supports the concept that reinstating creatine levels in patients with CTD could result in therapeutic efficacy.

Intranasal creatine administration increases brain creatine level and improves Barnes maze performance in rats

While skeletal muscle creatine levels can be enhanced by exogenous creatine supplementation, the elevation of brain creatine levels with oral creatine administration remains a challenge due to a lack of effective transportation of creatine through the blood-brain barrier. Intranasal administration can bypass the blood-brain barrier and deliver drugs directly to the brain. The purpose of this study was to assess the effect of intranasal administration of creatine on brain creatine level and cognitive performance. Rats were randomly assigned into three groups intranasal administration group, oral administration group, and control group. The intranasal group exhibited fewer errors and shorter primary latency compared to the control and oral groups, respectively, during the acquisition phase of the Barnes maze. The intranasal group spent a higher percentage of time in the target quadrant during the probe trial compared to the control group. Biochemical measurements showed that the concentration of creatine in the olfactory bulbs, medial prefrontal cortex, and hippocampus of the rats in the intranasal group was higher than in the oral, and control groups. These results indicate that intranasal administration of creatine hydrochloride increases the creatine level in the rat's brain's and improves their performance in the Barnes maze.

Creatine supplementation enhances anti-tumor immunity by promoting adenosine triphosphate production in macrophages

Creatine is an indispensable organic compound utilized in physiological environments; however, its role in immunity is still poorly understood. Here, we show that creatine supplementation enhances anti-tumor immunity through the functional upregulation of macrophages by increasing adenosine triphosphate (ATP) production. Creatine supplementation significantly suppressed B16-F10-originated tumor growth in mice compared with the control treatment. Under these conditions, intratumor macrophages polarized towards the M1 phenotype rather than the M2 phenotype, and there was an increase in tumor antigen-specific CD8+ T cells in the mice. The cytokine production and antigen-presenting activity in the macrophages were enhanced by creatine supplementation, resulting in a substantial increase in tumor antigen-specific CD8+ T cells. ATP upregulation was achieved through the cytosolic phosphocreatine (PCr) system via extracellular creatine uptake, rather than through glycolysis and mitochondrial oxidative phosphorylation in the macrophages. Blockade of the creatine transporter (CrT) failed to upregulate ATP and enhance the immunological activity of macrophages in creatine supplementation, which also impaired CD8+ T cell activity. Consequently, CrT blockade failed to suppress tumor growth in the creatine-supplemented mice. Thus, creatine is an important nutrient that promotes macrophage function by increasing ATP levels, ultimately contributing to enhanced anti-tumor immunity orchestrated by CD8+ T cells.

Dodecyl creatine ester improves cognitive function and identifies key protein drivers including KIF1A and PLCB1 in a mouse model of creatine transporter deficiency

Creatine transporter deficiency (CTD), a leading cause of intellectual disability is a result of the mutation in the gene encoding the creatine transporter SLC6A8, which prevents creatine uptake into the brain, causing mental retardation, expressive speech and language delay, autistic-like behavior and epilepsy. Preclinical in vitro and in vivo data indicate that dodecyl creatine ester (DCE) which increases the creatine brain content, might be a therapeutic option for CTD patients. To gain a better understanding of the pathophysiology and DCE treatment efficacy in CTD, this study focuses on the identification of biomarkers related to cognitive improvement in a Slc6a8 knockout mouse model (Slc6a8−/y) engineered to mimic the clinical features of CTD patients which have low brain creatine content. Shotgun proteomics analysis of 4,035 proteins in four different brain regions; the cerebellum, cortex, hippocampus (associated with cognitive functions) and brain stem, and muscle as a control, was performed in 24 mice. Comparison of the protein abundance in the four brain regions between DCE-treated intranasally Slc6a8−/y mice and wild type and DCE-treated Slc6a8−/y and vehicle group identified 14 biomarkers, shedding light on the mechanism of action of DCE. Integrative bioinformatics and statistical modeling identified key proteins in CTD, including KIF1A and PLCB1. The abundance of these proteins in the four brain regions was significantly correlated with both the object recognition and the Y-maze tests. Our findings suggest a major role for PLCB1, KIF1A, and associated molecules in the pathogenesis of CTD.

Cell-specific vulnerability to metabolic failure: the crucial role of parvalbumin expressing neurons in creatine transporter deficiency

Mutations in the solute carrier family 6-member 8 (Slc6a8) gene, encoding the protein responsible for cellular creatine (Cr) uptake, cause Creatine Transporter Deficiency (CTD), an X-linked neurometabolic disorder presenting with intellectual disability, autistic-like features, and epilepsy. The pathological determinants of CTD are still poorly understood, hindering the development of therapies. In this study, we generated an extensive transcriptomic profile of CTD showing that Cr deficiency causes perturbations of gene expression in excitatory neurons, inhibitory cells, and oligodendrocytes which result in remodeling of circuit excitability and synaptic wiring. We also identified specific alterations of parvalbumin-expressing (PV⁺) interneurons, exhibiting a reduction in cellular and synaptic density, and a hypofunctional electrophysiological phenotype. Mice lacking Slc6a8 only in PV⁺ interneurons recapitulated numerous CTD features, including cognitive deterioration, impaired cortical processing and hyperexcitability of brain circuits, demonstrating that Cr deficit in PV⁺ interneurons is sufficient to determine the neurological phenotype of CTD. Moreover, a pharmacological treatment targeted to restore the efficiency of PV⁺ synapses significantly improved cortical activity in Slc6a8 knock-out animals. Altogether, these data demonstrate that Slc6a8 is critical for the normal function of PV⁺ interneurons and that impairment of these cells is central in the disease pathogenesis, suggesting a novel therapeutic venue for CTD.