Imbalance between the function of Na+-K+-2Cl and K+-Cl impairs Cl- homeostasis in human focal cortical dysplasia

Ru Liu; Yue Xing; Herui Zhang; Junling Wang; Huanling Lai; Lipeng Cheng; Donghong Li; Tao Yu; Xiaoming Yan; Cuiping Xu; Yueshan Piao; Linghui Zeng; Horace H Loh; Guojun Zhang; Xiaofeng Yang

doi:10.3389/fnmol.2022.954167

Imbalance between the function of Na⁺-K⁺-2Cl and K⁺-Cl impairs Cl^- homeostasis in human focal cortical dysplasia

Front Mol Neurosci. 2022 Oct 17:15:954167. doi: 10.3389/fnmol.2022.954167. eCollection 2022.

Authors

Ru Liu^{1

2

3

4}, Yue Xing¹, Herui Zhang¹, Junling Wang^{1

2

3

4}, Huanling Lai¹, Lipeng Cheng^{1

3

4}, Donghong Li⁵, Tao Yu⁶, Xiaoming Yan⁶, Cuiping Xu⁶, Yueshan Piao⁷, Linghui Zeng⁸, Horace H Loh¹, Guojun Zhang⁶, Xiaofeng Yang^{1

4}

Affiliations

¹ Guangzhou Laboratory, Guangzhou, China.
² Beijing Tiantan Hospital, Capital Medical University, Beijing, China.
³ Beijing Institute of Brain Disorders, Capital Medical University, Beijing, China.
⁴ Neuroelectrophysiological Laboratory, Xuanwu Hospital, Capital Medical University, Beijing, China.
⁵ Department of Neurology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China.
⁶ Department of Functional Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing, China.
⁷ Department of Pathology, Xuanwu Hospital, Capital Medical University, Beijing, China.
⁸ Department of Pharmacology, Zhejiang University City College, Hangzhou, China.

Abstract

Objective: Altered expression patterns of Na⁺-K⁺-2Cl^- (NKCC1) and K⁺-Cl^- (KCC2) co-transporters have been implicated in the pathogenesis of epilepsy. Here, we assessed the effects of imbalanced NKCC1 and KCC2 on γ-aminobutyric acidergic (GABAergic) neurotransmission in certain brain regions involved in human focal cortical dysplasia (FCD).

Materials and methods: We sought to map a micro-macro neuronal network to better understand the epileptogenesis mechanism. In patients with FCD, we resected cortical tissue from the seizure the onset zone (SOZ) and the non-seizure onset zone (non-SOZ) inside the epileptogenic zone (EZ). Additionally, we resected non-epileptic neocortical tissue from the patients with mesial temporal lobe epilepsy (MTLE) as control. All of tissues were analyzed using perforated patch recordings. NKCC1 and KCC2 co-transporters expression and distribution were analyzed by immunohistochemistry and western blotting.

Results: Results revealed that depolarized GABAergic signals were observed in pyramidal neurons in the SOZ and non-SOZ groups compared with the control group. The total number of pyramidal neurons showing GABAergic spontaneous postsynaptic currents was 11/14, 7/17, and 0/12 in the SOZ, non-SOZ, and control groups, respectively. The depolarizing GABAergic response was significantly dampened by the specific NKCC1 inhibitor bumetanide (BUM). Patients with FCD exhibited higher expression and internalized distribution of KCC2, particularly in the SOZ group.

Conclusion: Our results provide evidence of a potential neurocircuit underpinning SOZ epileptogenesis and non-SOZ seizure susceptibility. Imbalanced function of NKCC1 and KCC2 may affect chloride ion homeostasis in neurons and alter GABAergic inhibitory action, thereby contributing to epileptogenesis in FCDs. Maintaining chloride ion homeostasis in the neurons may represent a new avenue for the development of novel anti-seizure medications (ASMs).

Keywords: cation-chloride cotransporters; epilepsy; focal cortical dysplasia; pyramidal neurons; seizure onset zone.