Tissue dynamics: development, regeneration and failure in human disease
Since we started the lab in 2004, we have been interested in the basic problem of
organ size control and its implications on human health and disease: how is the proper size of organs determined and maintained? What are the cellular origins of tissues? What are the molecular signals that control tissue mass homeostasis and regeneration?
We study these problems in the context of the developing and adult pancreas, aiming to obtain insights of relevance for diabetes and pancreatic cancer. Most of our work focuses on the biology of insulin-producing beta cells. We wish to understand how beta cells are generated during embryonic development and in postnatal life, what controls beta cell mass in healthy and disease conditions and the mechanisms of beta cell failure in diabetes. Our work utilizes advanced transgenic mouse models allowing for tissue specific and conditional genetic manipulations in vivo, as well as cadaveric human material and human blood samples.
In the last decade we have established a
non-invasive assay for detecting tissue-specific cell death in the human body. Dying cells release DNA fragments into the circulatory system. The DNA of each type of dying cell carries a unique pattern of DNA methylation. By detecting the unique methylation signatures of the circulating DNA, we can indicate its source tissue and recognize multiple disease processes - including diabetes, cancer, traumatic injury, and neurodegeneration in a highly sensitive and specific manner.
We work in very close collaboration with Ben Glaser (Hadassah medical center, Endocrinology). Additional local collaborators include Ittai Ben-Porath, Aharon Razin and Ruth Shemer (our department), Amir Eden (Hebrew University, Life Sciences), and Gidi Zamir, Adi Vaknin, Marc Gotkine, Aviad Zick, David Planer, Giora Landesberg and Zvi Friedlender (Hadassah medical center).
Our work is generously funded by the Juvenile Diabetes Research Foundation (JDRF), the European Union, the NIH (Human Islet Research Network), the Dutch friends of Hebrew University / DON foundation and the Israel Science Foundation.
Circulating cell-free DNA
Non-invasive detection of cell death in the human body
When cells die in the human body, their broken DNA is released to the circulation. Since each human tissue has a unique DNA methylation signature, analysis of methylation patterns in circulating DNA can in principle identify the tissue origins of cell-free circulating DNA as an indicator of cell death in specific tissues. We have developed a method to identify circulating DNA derived from specific tissues, and applied it to detect tissue-specific cell death in multiple pathologies including type 1 diabetes, cancer, neurodegeneration and trauma. We are working to develop this approach into a universal, minimally invasive methodfor early diagnosis and monitoring of multiple human diseases (Lehmann-Werman et al.,
PNAS 2016; Gala-Lopez, Neiman, et al.,
AMJ 2018; Zemmour et al.,
Nature Communications 2018; Lehmann-Werman et al.,
JCI Insight 2018; Moss et al.,
Nature Communications, 2018).
DNA methylation in pancreas development
The insulin gene promoter is unmethylated in beta cells but is heavily methylated elsewhere, providing a classic example of gene regulation by DNA methylation. We are studying how this pattern of methylation is established and what are the implications for developmental biology of the pancreas and for cellular plasticity in islets (Neiman et al.,
Pancreas and Beta cells
Glucose metabolism as a central regulator of beta cell biology
We have previously shown that glucose, acting via glucose metabolism, is a major physiological driver of beta cell replication and regeneration (Porat et al.,
Cell Metabolism 2011). More recently, we described how hyper-glycolysis may also be toxic to beta cells, and can specifically cause double strand breaks in the DNA and activation of the tumor suppressor p53 (Tornovsky-Babeay et al.,
Cell Metabolism 2014). Ongoing efforts are aimed at understanding the significance of DNA damage in beta cells and in diabetes, and the pathways mediating the toxic and mitogenic effects of glucose on beta cells.
Consequences of glucose metabolism in beta cells.The mitogenic effect of glucose mediated by classic GSIS pathway, specifically by calcineurin and insulin receptor controls replication.
The molecular signature of replicating beta cells
What does it mean to be a replicating beta cell in vivo? Which signaling pathways are active when quiescent beta cells enter the cell division cycle? Which genes are expressed in replicating beta cells? Are there any metabolic changes? Are there druggable targets? Answers to these questions require access to a pure population of replicating beta cells. However, beta cell replication is rare and current protocols for isolating these cells via FACS require fixation and processing that destroys sensitive biological material such as RNA. To overcome this problem we have developed a transgenic mouse strain that allows for the isolation of live replicating beta cells for global analysis of gene expression (Klochendler et al.,
Developmental Cell 2012; Klochendler et al.,
The Ccnb1-GFP transgene allows for the isolation of live replicating cells. Although GFP is expressed in all cells, it is rapidly degraded in quiescent (G0) and G1 cells (blue) and accumulates only in S/G2/M (green). In compound transgenic mice expressing Ccnb1-GFP and RipCre-RosaLSLTomato, quiescent (red) and replicating (yellow) beta-cells can be sorted live for RNA purification and transcriptome analysis.
Senescence in pancreas dynamics
We are studying in collaboration with Ittai Ben-Porath how cellular senescence affects the function and replication of pancreatic beta cells, and how this powerful tumor suppression mechanism affects tissue dynamics in the exocrine pancreas in the context of early stages of pancreatic cancer.
Effects of p16-induced senescence on beta cell function. Components of the senescence program that contribute to increased insulin secretion are highlighted in red (Helman et al.,
Nature Medicine 2016)