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Title: MicroRNA-184 : a multifaceted regulator of epidermal keratinocyte biology
Author: Richardson, A.
ISNI:       0000 0004 7657 1555
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2019
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The epidermis is vitally important in protecting the organism from environmental insults. Consisting of dynamic outer strata of keratinocytes that terminally differentiate from basal keratinocytes stem cells (KSC), the epidermis is maintained by constant spatial and temporal control. In psoriasis, a dysregulated and intensifying crosstalk between keratinocytes and immune cells disturbs epidermal homeostasis resulting in hyperproliferation and loss of differentiation. Recently, short (~22 nt) genetic molecules called microRNAs (miRNA) that regulate gene expression by repressing messenger RNA (mRNA) have gained attention as robust regulators of keratinocyte biology and key players in psoriasis. A specific miRNA elevated in psoriasis, miR-184, modulates the expression of Argonaute 2 (AGO2), an established effector of miRNA function. However, there is a paucity of research investigating miR-184 and the miR-184:AGO2 axis in epidermal keratinocyte biology. As such, the aim of this thesis was to delineate miR-184 expression and function during keratinocyte proliferation, differentiation and migration. Firstly, it was revealed that miR-184 was induced during keratinocyte differentiation in a process that relies exclusively on Ca2+ and the major keratinocyte Ca2+ entry pathway called store-operated calcium entry (SOCE). Furthermore, miR-184 was upregulated in a cohort of eight psoriasis patient samples. By modulating miR-184 expression it was elucidated that miR-184 promotes early keratinocyte differentiation through concomitant induction of factors related to DNA damage, growth arrest and terminal differentiation. In addition, this thesis reports the discovery of SOCE-dependent induction of miR-184 during keratinocyte migration as well as a long non-coding RNA, UCA1 that has been implicated in the regulation of miR-184. Importantly, ectopic miR-184 stimulated keratinocyte migration in scratched monolayers while inhibition of miR-184 reduced migration. Studies on AGO1-4 transcripts identified that AGO4 mRNA was the most abundant AGO in human epidermal keratinocytes and revealed no reduction of AGO2 expression in response to enhanced miR-184 levels during differentiation. Furthermore, both AGO1 and AGO4 were downregulated in psoriatic patients. Finally, it was established that AGO2 localises to the nucleus of terminally differentiated keratinocytes in a Ca2+-dependent mechanism, pointing to an apparent nuclear role for AGO2 during keratinocyte differentiation. In summary, the results reported in this thesis highlight an important role for miR-184 in the regulation of epidermal keratinocyte biology, reveal SOCE as a regulator of miRNA pathways in keratinocytes and show for the first time a role for miR-184 in epidermal keratinocyte migration. Together, these studies may facilitate the development of miRNA based dermaceuticals for cutaneous diseases.
Supervisor: Ross, K. ; Powell, A. ; Sexton, D. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: RM Therapeutics. Pharmacology