Nikolay Ninov Group
In vivo regeneration of β-cells as a future therapy for T1D
The pancreatic β-cells are the key metabolic sensors and effectors of insulin release, which is the only hormone known to lower blood glucose concentrations. Restoring of functional β-cell mass is recognized as a promising therapeutic avenue towards normalizing glycemic control in diabetes. Thus, our research goal is to understand the molecular and cellular events required for pancreatic β-cell regeneration, and apply this knowledge towards the development of cell replacement therapies for diabetes. To advance our knowledge on β-cell regeneration, we focus on defining new signals that promote the formation of functional β-cells in the body via processes of cell-fate conversion, cell plasticity and integration of the regenerated cells into functional and coordinated networks.
Regeneration of β-cells via cell plasticity: We have shown that zebrafish can naturally recover from extreme β-cell destruction and hyperglycemia by regenerating de novo insulin-secreting β-cells. This unique ability makes the zebrafish an exciting model organism to uncover the secrets of β-cell regeneration. To understand the underlying molecular principles, we have applied single-cell transcriptomics, in vivo imaging and conditional models of diabetes to build a “β-cell regeneration atlas”. Our regeneration atlas spans the period from β-cell destruction to the emergence of new insulin-producing cells. This atlas helped us to uncover one of the secrets behind the outstanding regenerative ability of the zebrafish. We discovered a previously unknown population of differentiated but phenotypically plastic cells, which in response to β-cell loss, undergo a partial conversion into insulin-expressing hybrid cells. We have shown that the formation of hybrid cells enables the resolution of diabetes in zebrafish (Singh et al., 2022). Our atlas of regeneration provides a rich source of information on the signals that control cell plasticity and restoration of functional islet cells, which we aim to exploit in order to restore regenerative capacity of human β-cells.
Specific questions to be investigated: What are the evolutionary principles underlying the conservation of regenerative ability in zebrafish as compared to mammals? Are the stem cells we found in zebrafish also present in human islets and how can they be harnessed for regenerative purposes? What are the similarities and differences between developmental and regenerative cell plasticity? What is the role of the innate and adaptive immune system, responding to tissue injury, in activating the regenerative response? How do the metabolic changes occurring after β-cell loss, including alterations in sugar metabolism, insulin levels and lipids, impact on the epigenetic landscape to promote cell plasticity and regeneration?
Leader β-cells coordinate Ca2+ dynamics across species in vivo: We have identified a critical subpopulation of β-cells present in both the zebrafish and the mouse pancreas, called leader cells, which initiate glucose-stimulated Ca2+ waves and act as islet-pacemakers (Salem et al., 2019) (Video 1). We showed that when leader cells are selectively deactivated or ablated, the response of the whole β-cell population is abrogated, indicating that leader cells initiate insulin release in response to blood sugar. We are exploring the role of leader cells in diabetes progression and islet dysfunction in models of type 1 and type 2 diabetes. To this end, we combine novel Optogenetic systems with Ca2+ imaging in the intact pancreas of the translucent zebrafish. This technology allows to selectively activate or deactivate individual islet cells by shining light on them while studying the effects on the function of the whole network of cells, not only the β-cells but also the α-cells (glucagon-producing) and δ-cells (somatostatin-producing) (→ Figure 1)
Specific questions to be studied: What signaling mechanisms define which β-cells will become leaders and which ones followers? Are leader cells stable in time or do they alternate with non-leader cells? Can leader-cells undergo selective loss of dysfunction under conditions of T2D? Can leader cells regenerate and what are the molecular markers of a leader cell? How do leader cells communicate with the rest of the islet cells to control their activity?
Future Projects and Goals
- Exploring cell plasticity for tissue regeneration - from zebrafish to human
- Defining the role of pacemaker β-cells in establishing functional networks in health and disease
- Increasing the resilience of the islet cells to withstand and thrive under stressful conditions, such as immune attack and metabolic pressure
Methodological and Technical Expertise
- Single-cell genomics
- Optogenetics and Ca2+ imaging in vivo
- Drug discovery
- Zebrafish genetics
- Diabetes, metabolism and islet biology