A new rat model of creatine transporter deficiency reveals behavioral disorder and altered brain metabolism

Lara Duran-Trio,Jocelyn Grosse,Carmen Sandi,Stephen J Bruce,Gabriella Fernandes-Pires,Clothilde Roux-Petronelli,Dunja Simicic,Olivier Braissant,Cristina Cudalbu,Pierre-Alain Binz

doi:10.1038/s41598-020-80824-x

Abstract

Creatine is an organic compound used as fast phosphate energy buffer to recycle ATP, important in tissues with high energy demand such as muscle or brain. Creatine is taken from the diet or endogenously synthetized by the enzymes AGAT and GAMT, and specifically taken up by the transporter SLC6A8. Deficit in the endogenous synthesis or in the transport leads to Cerebral Creatine Deficiency Syndromes (CCDS). CCDS are characterized by brain creatine deficiency, intellectual disability with severe speech delay, behavioral troubles such as attention deficits and/or autistic features, and epilepsy. Among CCDS, the X-linked creatine transporter deficiency (CTD) is the most prevalent with no efficient treatment so far. Different mouse models of CTD were generated by doing long deletions in the Slc6a8 gene showing reduced brain creatine and cognitive deficiencies or impaired motor function. We present a new knock-in (KI) rat model of CTD holding an identical point mutation found in patients with reported lack of transporter activity. KI males showed brain creatine deficiency, increased urinary creatine/creatinine ratio, cognitive deficits and autistic-like traits. The Slc6a8Y389C KI rat fairly enriches the spectrum of CTD models and provides new data about the pathology, being the first animal model of CTD carrying a point mutation.

Highlights

Creatine is an organic compound used as fast phosphate energy buffer to recycle ATP, important in tissues with high energy demand such as muscle or brain
To obtain a model as near as possible of the human creatine transporter deficiency (CTD), a knock-in (KI) rat was generated with the SLC6A8 c.1166A > G; p.(Tyr389Cys) missense mutation found in human patients and reported with no functional activity of the transporter[17] (Fig. 1)
CTD patients are characterized by CNS Cr deficiency and are diagnosed, as all Creatine Deficiency Syndromes (CCDS) patients, using brain 1H-MRS

Summary

Introduction

Creatine is an organic compound used as fast phosphate energy buffer to recycle ATP, important in tissues with high energy demand such as muscle or brain. CCDS are characterized by brain creatine deficiency, intellectual disability with severe speech delay, behavioral troubles such as attention deficits and/or autistic features, and epilepsy. Different mouse models of CTD were generated by doing long deletions in the Slc6a8 gene showing reduced brain creatine and cognitive deficiencies or impaired motor function. CCDS are characterized by brain Cr deficiency, intellectual disability with severe speech delay, behavioral abnormalities such as attention deficits and/or autistic features, and seizures for GAMT and SLC6A8 d eficiencies[7]. 1H-MRS evaluates whether Cr is deficient in the brain, the common feature in all CCDS; urine analysis tests for the specific biochemical marker of CTD (increased urinary Cr/Crn ratio). CrT knock-out (KO) mouse males with ubiquitous deletions of the exons 2–49,16 or 5–712–14 showed brain creatine deficiency and decreased body weight, features present in CTD patients[17]. While ubiquitous deletion of the exons 2–4 after tamoxifen induction in neonatal and adult mice led to brain Cr deficiency and lower body weight, cognitive deficits were only present if the induction was during the neonatal period highlighting the important role of Cr during brain d evelopment[10]

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