Browsing by Subject "Kir4.1"

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    Tumor Necrosis Factor Alpha (TNF-α) Disrupts Kir4.1 Channel Expression Resulting in Müller Cell Dysfunction in the RetinaDiurnal Rhythm of Kir4.1 in the Retina
    (ARVO, 2017-05-01) Hassan, Iraj; Luo, Qianyi; Majumdar, Sreeparna; Dominguez, James M.; Busik, Julia V.; Bhatwadekar, Ashay D.; Department of Ophthalmology, IU School of Medicine
    Purpose: Diabetic patients often are affected by vision problems. We previously identified diabetic retinopathy (DR) as a disease of clock gene dysregulation. TNF-α, a proinflammatory cytokine, is known to be elevated in DR. Müller cells maintain retinal water homeostasis and K+ concentration via Kir4.1 channels. Notably, Kir4.1 expression is reduced in diabetes; however, the interplay of TNF-α, Kir4.1, and clock genes in Müller cells remains unknown. We hypothesize that the Kir4.1 in Müller cells is under clock regulation, and increase in TNF-α is detrimental to Kir4.1. Methods: Long-Evans rats were made diabetic using streptozotocin (STZ). Retinal Kir4.1 expression was determined at different time intervals. Rat Müller (rMC-1) cells were transfected with siRNA for Per2 or Bmal1 and in parallel treated with TNF-α (5–5000 pM) to determine Kir4.1 expression. Results: Kir4.1 expression exhibited a diurnal rhythm in the retina; however, with STZ-induced diabetes, Kir4.1 was reduced overall. Kir4.1 rhythm was maintained in vitro in clock synchronized rMC-1 cells. Clock gene siRNA-treated rMC-1 exhibited a decrease in Kir4.1 expression. TNF-α treatment of rMCs lead to a profound decrease in Kir4.1 due to reduced colocalization of Kir4.1 channels with synapse-associated protein (SAP97) and disorganization of the actin cytoskeleton. Conclusions: Our findings demonstrate that Kir4.1 channels possess a diurnal rhythm, and this rhythm is dampened with diabetes, thereby suggesting that the increase in TNF-α is detrimental to normal Kir4.1 rhythm and expression.
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    Type 2 diabetes disturbs Kir4.1 rhythm in retinal Müller cells
    (Office of the Vice Chancellor for Research, 2016-04-08) Luo, Qianyi; Bhatwadekar, Ashay
    The Müller cells function as a principal glia of the retina and maintain water homeostasis and K+ concentration via the specialized inwardly rectifying K+ (Kir) channels. About six to seven Kir channels have been found, among which Kir4.1 is expressed abundantly in Müller cells. Diabetes leads to a decrease in Kir4.1 expression and of potassium currents. For this study, we hypothesized that a diurnal change in Müller cell metabolism plays an important role in regulating the Kir4.1 expression. We tested our hypothesis using an animal model of type 2 diabetes (T2D;db/db mice) and in an in vitro study on the rat Müller (rMC-1) cells. The electroretinogram (ERG) assessment was performed on db/db mice to evaluate the Müller cell dysfunction. The rhythm of protein expression of Kir4.1 was examined in rMC-1 cells by western blot. The ‘b’ wave of an ERG, a characteristic of K+ ion distribution across the retina exhibited a diurnal rhythm in a mouse retina. The oscillatory pattern of ERG response was profoundly dampened in db/db mice. The clock synchronized rMC-1 cells in vitro exhibited a consistent oscillatory pattern for clock genes. The Kir4.1 protein in rMC-1 cells showed a regular pattern of the peak and troughs, consistent with the functional cock. Our studies suggest that Kir4.1 channels possess a diurnal rhythm and with T2D this rhythm is dampened.