The Merkle laboratory uses human pluripotent stem cell (hPSC)-derived culture systems to uncover the mechanistic basis of human neurological diseases. Our primary focus is obesity, which leads to millions of premature deaths each year and which lacks broadly effective treatments. Genetic studies demonstrate that obesity is largely a disease of the brain, and that neuron populations in the hypothalamus are essential regulators of food intake and energy expenditure. In order to study these cells, we have developed methods to differentiate hPSCs into functional hypothalamic neurons. We study their function in health and disease using genome engineering, single-cell transcriptomics, quantitative proteomics, high content imaging, calcium imaging, and xenotransplantation. Research in the Merkle laboratory is focused on three areas:
1) Models of hypothalamic development and obesity
Our differentiation protocols generate a broad array of behaviourally and physiologically relevant hypothalamic cell types that generate and secrete bioactive peptides in a manner consistent with what is observed in primary human brain in vivo. We study how these hPSC-derived hypothalamic neurons develop in vitro to provide molecular insights into brain patterning and neurogenesis. This culture system is also ideal for studying how hypothalamic neurons sense and functionally respond to hormones (e.g. leptin), nutrients and drugs. We hypothesize that primary cilia act as signalling platforms to mediate nutritional sensing, and are approaching this question using proteomic and histological methods. Finally, we are studying how obesity-associated mutations and environmental factors alters the function of hypothalamic neurons. In particular, we use CRISPR/Cas9 to introduce human obesity-associated mutations, and are developing co-culture systems and reduced cultures of purified neurons to examine the role of other cell types and secreted factors on hypothalamic neuron function. Together, these studies have the potential to provide molecular and cellular mechanisms that bridge the gulf between human genetic data and organismic phenotypes.
2) Therapeutic translation & in vivo models
Since the melanocortin system plays key roles in regulating energy homeostasis and since some anti-obesity drugs are known to act on these cells, we hypothesise that other drugs acting on these cells may more effectively reduce appetite and body weight. We are therefore screening for compounds that promote the activity and peptide secretion of target hypothalamic neuron populations in vitro to facilitate their testing in animal models of obesity. In addition, we have previously demonstrated that human hypothalamic neurons survive transplantation into the mouse brain, and are interested in extending these studies to test the functional effects of transplanted human neurons on feeding behaviour and body weight.
3) Genetic variants in human stem cells
Understanding the genetic background of hPSCs is essential for both correctly interpreting the results of in vitro disease models, and ensuring the safety of cellular products to be transplanted into humans in the context of regenerative medicine. For example, we recently showed that hPSCs recurrently acquire cancer-associated mutations in the tumour suppressor TP53 (p53) that confer strong selective advantage, but little is known about which genetic variants are present in which hPSC lines or their phenotypic consequences. We are pursuing these interests as part of the UK Regenerative Medicine platform using whole genome and exome sequencing, cellular competition assays, and live imaging with the aims of identifying phenotypically important genetic variants and identifying culture methods that reduce cellular stress and the acquisition or selection for mutations.
Outstanding graduate and postdoctoral candidates interested in joining our team are encouraged to write me directly.
Kirwan P, Kay RG, Brouwers B, Herranz-Pérez V, Jura M, Larraufie P, Jerber J, Pembroke J, Bartels T, White A, Gribble FM, Reimann F, Farooqi IS, O’Rahilly S, Merkle FT§. Quantitative mass spectrometry for human melanocortin peptides in vitro and in vivo suggests prominent roles for β-MSH and desacetyl α-MSH in energy homeostasis. Mol Metab. Mol Metab. Epub Aug21, 2018. DOI: 10.1016/j.molmet.2018.08.006. PMID:30201275.
Merkle FT*, Ghosh S*, Kamataki N, Mitchell J, Avior Y, Mello C, Kashin S, Mekhoubad S, Ilic D, Charlton M, Saphier G, Handsaker RE, Genovese G, Bar S, Benvenisty N, McCarroll S, Eggan K. Human pluripotent stem cells recurrently acquire and expand dominant negative P53 mutations. Nature, E-pub. 26 April 2017. DOI 10.1038/nature22312. PMID: 28445466 PMC5427175.
Merkle FT*, Neuhausser WM*, Santos D, Valen E, Gagnon JA, Maas K, Sandoe J, Schier AF, Eggan K. Efficient CRISPR-Cas9-mediated generation of knockin human pluripotent stem cells lacking undesired mutations at the targeted locus. Cell Rep. 2015 May 12;11(6):875-83. doi: 10.1016/j.celrep.2015.04.007. PMID: 25937281.PMCID:PMC5533178
Merkle FT, Maroof A, Wataya T, Sasai Y, Studer L, Eggan K, Schier AF. Generation of neuropeptidergic hypothalamic neurons from human pluripotent stem cells. Development. 2015 Feb 15;142(4):633-43. doi: 10.1242/dev.117978. PMID:25670790. PMCID:PMC4325380
Merkle FT, Eggan K. Modeling human disease with pluripotent stem cells: from genome association to function. Cell Stem Cell. 2013 Jun 6;12(6):656-68. doi: 10.1016/j.stem.2013.05.016. PMID:23746975.
Additional publications are available at: http://www.ncbi.nlm.nih.gov/pubmed/?term=merkle+ft