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Tau Tubulin Kinase TTBK2 Sensitivity of Glutamate Receptor GluK2
Kristina Nieding1, Veronika Matschke, Sven G Meuth
1Department of Cardiovascular Medicine, Institute for Genetics of Heart Diseases (IfGH), University Hospital Muenster, Muenster, Germany.
Background/Aims:
Inherited, autosomal dominant spinocerebellar ataxia type 11 (SCA11) is caused by loss of function mutations of TTBK2 (tau tubulin kinase 2). Mutations observed in patients with SCA11 include truncated TTBK2(450). The present study explored the possibility that TTBK2 influences the function of the glutamate receptor GluK2.
Methods:
GluK2 was expressed in Xenopus oocytes without and with additional expression of wild type TTBK2, the truncated mutant TTBK2(450), or the kinase dead mutants TTBK2(KD) and TTBK2(450/KD). GluK2 current was determined by dual electrode voltage clamp and GluK2 protein abundance in the cell membrane utilizing confocal microscopy.
Results:
Glutamate exposure of GluK2 expressing oocytes generated a current, which was significantly lower in oocytes expressing GluK2 together with TTBK2 wt or TTBK2(KD) than in oocytes expressing GluK2 alone or together with either TTBK2(450) or TTBK2(450/KD). According to confocal microscopy of EGFP-tagged GluK2, TTBK2 wt decreased the GluK2 protein abundance in the cell membrane. Overexpression of an inactive RAB5(N133I) mutant but not RAB5wt could reverse the TTBK2 effect on GluK2 suggesting that RAB5 function is required for the effect.
Conclusions:
TTBK2 down-regulates GluK2 activity by decreasing the receptor protein abundance in the cell membrane via RAB5-dependent endocytosis, an effect that may protect against neuroexcitotoxicity.
Insights
Tau tubulin kinase 2 (TTBK2) down-regulates glutamate receptor GluK2 activity by reducing its cell membrane abundance. This TTBK2-mediated process, involving RAB5-dependent endocytosis, may offer neuroprotection against excitotoxicity.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Spinocerebellar ataxia type 11 (SCA11) is an inherited disorder linked to loss-of-function mutations in TTBK2.
- Specific mutations, like the truncated TTBK2(450), are observed in SCA11 patients.
- The study investigates the potential role of TTBK2 in regulating the glutamate receptor GluK2.
Purpose of the Study:
- To determine if TTBK2 influences the function and cell surface expression of the glutamate receptor GluK2.
- To elucidate the mechanism by which TTBK2 might affect GluK2, particularly in the context of SCA11-associated mutations.
Main Methods:
- Expressed GluK2 in Xenopus oocytes alongside wild-type TTBK2, truncated TTBK2(450), or kinase-dead mutants.
- Measured GluK2 channel activity using dual electrode voltage clamp.
- Quantified GluK2 protein levels at the cell membrane via confocal microscopy.
Main Results:
- TTBK2 (wild-type and kinase-dead) significantly reduced GluK2-mediated current compared to GluK2 alone or with truncated/inactive mutants.
- Confocal microscopy revealed that wild-type TTBK2 decreases GluK2 protein abundance in the cell membrane.
- RAB5-dependent endocytosis, indicated by the effect of a RAB5(N133I) mutant, is implicated in TTBK2's regulation of GluK2.
Conclusions:
- TTBK2 down-regulates GluK2 activity by promoting its endocytosis and reducing cell membrane abundance.
- This mechanism is dependent on RAB5-mediated endocytosis.
- The findings suggest a potential protective role of TTBK2 against neuroexcitotoxicity.
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