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Xingjian Jin 04.23.2014correctedtmg.pdf (4.03 MB)

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Regulation of Calcium Signaling by Primary Cilia and Its Role in Polycystic Kidney Disease Pathogenesis

Jin, Xingjian
http://rave.ohiolink.edu/etdc/view?acc_num=mco1396564595

Abstract Details

2014, Doctor of Medicine and Doctor of Philosophy, University of Toledo, College of Medicine.
The primary cilium is a solitary organelle present in the majority of mammalian cells. The cilium has been implicated in a variety of cellular events. By virtue of its structure and cellular location, the most important and well-known function of primary cilium is sensation. Projected from the apical membrane of a cell to extracellular environment, the cilium senses stimulations from the extracellular matrix and translates each cue into second messengers in intracellular signaling pathways. Among these messengers, calcium is proposed to be the most important. Thus, dysfunctional cilia might lead to abnormal calcium signaling and consequently, several diseases, collectively referred as “ciliopathies”. Our study has two goals. First, we aim to show that the cilium is an independent cellular compartment for calcium signaling evoked by both mechanical and chemical stimulation. To date, though many studies have related cilia to calcium signaling, there is no direct evidence showing where and how the calcium influx initially occurs. Without such evidence, the critical first step of cilia-mediated calcium signaling remains speculative. To test our hypothesis, we developed a novel imaging and cell culture system to visualize calcium signaling within an individual cilium. Then we apply different stimulations to cell and observe subsequent responses. Using this advanced system we show for the first time that following extracelluar stimulation, calcium flux into the cilia body, or cilioplasm. However, cells have different responses to different stimulations. When fluid shear-stress is applied, calcium enters into the cilioplasm and such calcium signals are further amplified in the cytoplasm. In contrast, in the case of chemical stimulation, such as fenoldopam, a dopamine receptor-type 5 (DR5) agonist, calcium signals are contained exclusively in the cilioplasm. Also, we examine the effects of different signaling pathway inhibitors or siRNA on ciliary calcium responses. Echoes to previous studies, we find that the flow-induced calcium signaling is dependent on polycystin-2 (PC2) calcium channel, whereas Fenoldopam-induced calcium influx is through L-type calcium channel (Cav1.2). Additionally, we find that the flow-induced calcium signaling cascade is regulated by ryanodine receptor through calcium induced calcium release. Our second aim is to identify the role of Cav1.2 inhibition in the pathogenesis and progression of polycystic kidney disease (PKD). Lower intracellular calcium level has been reported in cells isolated from cyst linings. However, if other calcium channels than PC2 can affect intracellular calcium level and implicate in PKD pathogenesis is unknown. In clinical practice, L-type calcium channel blockers have been well prescribed for hypertensive patients. It’s noteworthy that such drugs are generally avoided in hypertensive PKD patients for their putative adverse effects on PKD. However, how L-type calcium channel blockers accelerate cyst formation remains unclear. In our study, we observe significant decreases of already lowered intracellular calcium level in PKD cells with Cav1.2 knockdown. Such reduction further causes irregular AKT and ERK phosphorylation. As we expected, abnormal mitogenesis signaling leads to more severe mitosis catastrophe and higher proliferation rate. Consequently, when Cav1.2 is inhibited in PKD animal models, much larger cysts are observed at an earlier stage. We thus propose that Cav1.2 work in concert with PC2 as cilia related calcium channel to maintain intracellular calcium homeostasis and loss of Cav1.2 in PKD cells can lead to abnormal mitosis and cell division, which facilitate the formation of cysts.
Surya Nauli (Advisor)
107 p.
Biology
Cilia, PKD, calcium signaling

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Citations

  • Jin, X. (2014). Regulation of Calcium Signaling by Primary Cilia and Its Role in Polycystic Kidney Disease Pathogenesis [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=mco1396564595

    APA Style (7th edition)

  • Jin, Xingjian. Regulation of Calcium Signaling by Primary Cilia and Its Role in Polycystic Kidney Disease Pathogenesis. 2014. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=mco1396564595.

    MLA Style (8th edition)

  • Jin, Xingjian. "Regulation of Calcium Signaling by Primary Cilia and Its Role in Polycystic Kidney Disease Pathogenesis." Doctoral dissertation, University of Toledo, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=mco1396564595

    Chicago Manual of Style (17th edition)

mco1396564595
446
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This open access ETD is published by University of Toledo Health Science Campus and OhioLINK.