Functional characterisation of microRNA-125b in pancreatic β-cells
File(s)
Author(s)
Cheung, Rebecca
Type
Thesis
Abstract
Pancreatic β-cells in the islets of Langerhans regulate glucose homeostasis by secreting insulin in response to elevated levels of glucose in the circulation and impairment of their function can contribute to the development of type 2 diabetes (T2D). MicroRNAs (miRNAs) are short non-coding RNAs that silence gene expression post-transcriptionally and play a vital role in the development and function of endocrine cells. MiRNAs fine-tune the expression of β-cell genes to regulate glucose homeostasis whilst their own expression is altered in T2D. MiR-125b-5p (miR-125b) is a highly conserved miRNA that is ubiquitously expressed and targets
many genes in a cell-specific manner. Its role is well characterized in diseases such as cancer,
but in β-cells remains unclear. Islet miR-125b expression is upregulated by glucose through
the energy sensor, AMP-activated protein kinase (AMPK), and positively correlates with body mass index (BMI) in human islet donors. Thus, we hypothesized that miR-125b may contribute
to the deleterious effects of hyperglycaemia in β-cells and aimed to determine the function of miR-125b in these cells. Here, I show that CRISPR/Cas9 mediated knockout of miR-125b in
a human β-cell line (EndoCβ-H1) enhances glucose-stimulated insulin secretion (GSIS) and
results in shorter, more fragmented mitochondria, whilst overexpression of miR-125b in a mouse insulinoma cell line (MIN6) results in reduced insulin content, the appearance of
enlarged lysosomes and protects cells against cytokine-induced β-cell death. Importantly,
overexpression of miR-125b in β-cells of mice causes impairments in glucose tolerance due
to defects in insulin secretion, attributed to the strong reduction in mature insulin granule
content and crystallization and abnormally enlarged lysosomes. Furthermore, miR-125b has
a profound impact on the expression of genes involved in lysosomal and mitochondrial
function in β-cells. In summary, my study has shown that miR-125b is a negative regulator of insulin secretion and a potential fine-tuner of mitochondrial and lysosomal metabolism in β-cells. My findings provide new insights into the role of miR-125b in β-cell function and point towards the inhibition of this miRNA in these cells as a potential therapeutic approach for the treatment of T2D.
many genes in a cell-specific manner. Its role is well characterized in diseases such as cancer,
but in β-cells remains unclear. Islet miR-125b expression is upregulated by glucose through
the energy sensor, AMP-activated protein kinase (AMPK), and positively correlates with body mass index (BMI) in human islet donors. Thus, we hypothesized that miR-125b may contribute
to the deleterious effects of hyperglycaemia in β-cells and aimed to determine the function of miR-125b in these cells. Here, I show that CRISPR/Cas9 mediated knockout of miR-125b in
a human β-cell line (EndoCβ-H1) enhances glucose-stimulated insulin secretion (GSIS) and
results in shorter, more fragmented mitochondria, whilst overexpression of miR-125b in a mouse insulinoma cell line (MIN6) results in reduced insulin content, the appearance of
enlarged lysosomes and protects cells against cytokine-induced β-cell death. Importantly,
overexpression of miR-125b in β-cells of mice causes impairments in glucose tolerance due
to defects in insulin secretion, attributed to the strong reduction in mature insulin granule
content and crystallization and abnormally enlarged lysosomes. Furthermore, miR-125b has
a profound impact on the expression of genes involved in lysosomal and mitochondrial
function in β-cells. In summary, my study has shown that miR-125b is a negative regulator of insulin secretion and a potential fine-tuner of mitochondrial and lysosomal metabolism in β-cells. My findings provide new insights into the role of miR-125b in β-cell function and point towards the inhibition of this miRNA in these cells as a potential therapeutic approach for the treatment of T2D.
Version
Open Access
Date Issued
2021-06
Date Awarded
2021-12
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Martinez-Sanchez, Aida
Rutter, Guy
Sponsor
Medical Research Council (Great Britain)
Publisher Department
Department of Metabolism, Digestion and Reproduction
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)