Expression and functional importance of microglial Kv1.3 channels in Alzheimer's Disease Open Access

Rangaraju, Srikant (2016)

Permanent URL: https://etd.library.emory.edu/concern/etds/rj4305338?locale=en
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Abstract

Alzheimer's disease (AD) is the commonest dementing illness worldwide but no disease-modifying therapy exists. Accumulation and aggregation of toxic amyloid beta (Aβ) result in neurotoxicity and neuroinflammation, both of which lead to neurodegeneration and disease progression. Recent genetic studies have suggested that the innate macrophages of the brain called microglia are the key mediators of neuroinflammation in AD. Kv1.3, a voltage-gated potassium channel expressed by microglia, is a key regulator of membrane potential, calcium signaling and neurotoxic effects of activated microglia in-vitro and may represent a therapeutic target for drugs that inhibit neurotoxic microglial functions in AD. However, Kv1.3 channel expression patterns in the human AD brain are currently unknown. The importance of Kv1.3 channels in Aβ-induced pro-inflammatory microglial responses is also unknown. We hypothesized that (1) Activated microglia in human AD express Kv1.3 potassium channels at higher levels than in non-AD brains, and (2) Kv1.3 channels regulate Aβ-included microglial activation and effector functions in-vitro. In a blinded post-mortem immunohistochemical semi-quantitative analysis performed on ten Alzheimer's disease patients and 10 non-disease controls, we observed a significantly higher Kv1.3 staining intensity (p=0.03) and Kv1.3-positive cell density (p=0.03) in the frontal cortex of AD brains, compared to controls. This paralleled an increased number of Iba1-positive microglia in AD brains. We further confirmed increased Kv1.3 expression in AD brain by an objective and quantitative image analysis approach in hippocampal cortical sections from an independent sample of 5 AD and 5 non-AD cases. Increased Kv1.3 expression was also confirmed by western blot analysis of AD brain samples. Kv1.3-positive cells had microglial morphology and were associated with amyloid-β plaques. In immunofluorescence studies, Kv1.3 channels co-localized with Iba1 but not with astrocyte marker GFAP, confirming that elevated Kv1.3 expression in AD is limited to microglia. Consistent with our hypotheses, Aβ-induced reactive oxygen species productions as well as Aβ-induced impairment of microglial chemotaxis were inhibited by Kv1.3 channel blockade in-vitro. Our results demonstrate that Kv1.3 channels are highly expressed by microglia in human AD and also confirm that Kv1.3 channel blockade represents a promising strategy to inhibit pro-inflammatory microglial functions in AD.

Table of Contents

(A) INTRODUCTION... 1-2

(B) BACKGROUND... 3-6

(C) METHODS... 7-14

(D) RESULTS

D1. Aim 1... 15-16 D2. Aim 2... 17-18

(E) DISCUSSION... 19-23

(F) REFERENCES... 24-26

(G) TABLES... 27-28

a. Table 1... 27 b. Table 2... 28

(H) FIGURES... 29-40

a. Figure 1... 29 b. Figure 2... 30-31 c. Figure 3... 32-33 d. Figure 4... 34 e. Figure 5... 35 f. Figure 6... 36 g. Figure 7... 37 h. Figure 8... 38

i. Figure 9... 39-40

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