Dr Maria Fragiadaki

1) Which signalling pathways are critical in the development of Autosomal Dominant Polycystic Kidney Disease?

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a monogenic, multi-organ disease affecting both the kidneys and the vasculature, currently remaining without a cure. The molecular mechanisms leading to pathogenesis are poorly understood.
To address this, I have received funding from the Academy of Medical Sciences (Springboard Fellowship Award - 2018-2020) to combine RNAseq transcriptomics and functional siRNA screening technologies to identify and characterize key genes involved in cystogenesis (the generation of cysts).

2) How does Ankyrin Repeat and Single KH Domain 1 (ANKHD1) enhance cystic disease?

Ankyrin Repeat and Single KH Domain 1 (ANKHD1) is a protein first discovered in Drosophila as a regulator of photoreceptor development (https://www.ncbi.nlm.nih.gov/pubmed/11782402). Recently I uncovered that ANKHD1 controls cell proliferation by directly binding to and modulating a subset of tumour-suppressor microRNAs (https://www.ncbi.nlm.nih.gov/pubmed/29695508). microRNAs are involved in the pathology of polycystic kidney disease, which is also a condition characterized by increased proliferation and elevated JAK/STAT signalling. We have established models to study cyst progression both in vitro (Figure 1) and in vivo (Figure 2). I am currently investigating the molecular mechanism employed by ANKHD1 to control proliferation in ADPKD via JAK/STAT regulation. This work is funded by Kidney Research UK via my Intermediate Fellowship (2015-2019).

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Figure 1: We use human ADPKD-derived cells which grow in three-dimensional organotypic cultures. Microscopic cysts arise which grow in size over several days. With this model we can inhibit gene expression either pharmacologically or with gene silencing strategies. We can enhance gene expression by cytokine stimulation and/or gene editing. Growth of cysts is then measured over several days and therefore inform us if a novel gene or drug may affect in vitro cystogenesis. This approach is complementary to our mouse genetic models and studies of human samples.

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Figure 2: A Mouse model of polycystic kidney disease in the Fragiadaki Lab. Kidneys sections were stained with H&E. Right panel shows kidney section from mice where the Pkd1 gene was deleted in the kidney resulting in polycystic kidney disease; on the left the wild-type littermate control kidneys can be seen.

3) Can Growth-hormone antagonism prove beneficial in treating ADPKD?

I have recently made the novel observation that growth hormone is enhanced by 10-fold in mice with polycystic kidneys (https://www.ncbi.nlm.nih.gov/pubmed/28104302). Growth hormone (GH) can activate JAK/STAT signalling via engaging with growth hormone receptors, which are present in the kidney (figure 3). To study proof-of-principle whether GH is contributing to disease, I have received funding in the form of a PhD studentship (2017-2020; held by Ms Fiona MacLeod) to examine whether a novel GH antagonist can reduce cyst formation in mouse and human models of ADPKD.4) Is JAK2/STAT5 involved in the development of endothelial dysfunction?

A common symptom of ADPKD is the development of endothelial dysfunction and associated intracranial aneurysms. We have strong evidence that STAT5 is expressed in vascular endothelial cells where it regulates inflammation (figure 4). To explore the role of STAT5 in vascular inflammation further I initiated a collaboration with Prof Paul C Evans, together we received a British Heart Foundation project grant (2017-2020). Dr Hannah Roddie is currently performing RNA-seq to identify the repertoire of genes affected by STAT5 in the vasculature and perform studies in genetic mouse models of endothelial dysfunction.

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Figure 3: Confocal microscopy of renal kidney sections. Top panels show normal mouse kidney epithelial cells expressing GHR (left) and STAT5 (right), while the bottom panels show GHR (left) and STAT5 (right) distribution in polycystic kidneys. 

4) Is JAK2/STAT5 involved in the development of endothelial dysfunction?

A common symptom of ADPKD is the development of endothelial dysfunction and associated intracranial aneurysms. We have strong evidence that STAT5 is expressed in vascular endothelial cells where it regulates inflammation (figure 4). To explore the role of STAT5 in vascular inflammation further I initiated a collaboration with Prof Paul C Evans, together we received a British Heart Foundation project grant (2017-2020). Dr Hannah Roddie is currently performing RNA-seq to identify the repertoire of genes affected by STAT5 in the vasculature and perform studies in genetic mouse models of endothelial dysfunction.

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Figure 4: En face staining of STAT5 followed by confocal microscopy. STAT5 was deleted in endothelial cells by crossing the endothelial-SCL-Cre-ERT into the STAT5A/B fl/fl mouse, resulting in STAT5 deletion specifically in endothelial cells following tamoxifen injections.