Identifying the molecular mechanisms leading to age-related chronic disease onset using an innovative in vivo setup

Diabetes is an umbrella term for a group of energy metabolism diseases defined by chronically increased blood sugar levels (hyperglycemia). Hyperglycemia is caused by the inability of the body to produce and/or use sufficient insulin, a hormone produced in the pancreatic islet by the beta-cells. The two most common forms of diabetes are characterized by a complex etiology, consequently making their study extremely difficult. The project addressed this challenge by studying the fate of the insulin-producing beta-cells fate in a group of monogenic disorders, termed MODY (Maturity Onset Diabetes of the Young). Briefly we first in vitro differentiated induced-pluripotent stem cells derived either from healthy subjects or MODY1 (HNF4A mutation) and MODY3 (HNF1A mutation) patients towards pancreatic endocrine islet cells fate. Dissociated pancreatic progenitors or immature islet cells were encapsulated in alginate and further xenotransplanted in either normoglycemic or genetically induced humanized diabetic mice. At different time points after transplantation the beads were retrieved and analyzed by large-scale microscopy, next generation sequencing and proteomics. By using this approach, we established that: (1) encapsulation promotes the islet cell differentiation potential (Legøy*, Vethe* et al. [Chera], Sci Reports, 2020), (2) hyperglycemia impacts the cell identity restriction, causing either mixed cell identity or death according to the exposure time (Legøy et al. [Chera], Acta Physiol, 2019), (3) transplanting the cells into the in vivo environment improves cell identity and this effect is dependent on the induction of HNF1A and HNF4A factors. Both HNF4A and HNF1A mutations affect the restriction and maintenance of the hormone expression choice (Legøy et al., [Chera], Frontiers in Cell and Developmental Biology). Based on this study, we advance a model in which immediately after transplantation the in vivo environment promotes the islet profile in the differentiating pancreas progenitor cells, manifested by ameliorating their hormone expression phenotype. This probably occurs via an improved energy metabolism, influencing the activity of specific epigenetic modifiers, such as MECP2. The underlying mechanism is at least partially dependent on the optimal levels of HNF1A and HNF4A, as decreased expression of these transcription factors (as observed in MODY1 and MODY3 patients) not only cancel the observed confinement towards single hormone expression, but also triggers an accumulation of immature bihormonal cells. Another important conclusion of this study is that the effects of the HNF factor mutations characterizing MODY1 or MODY3 cells are revealed only after being exposed to the in vivo environment and impact the pancreatic progenitor recruitment as well as the cell identity restriction (i.e. cell fate selection).

6 different datasets obtained in this study are publicly available to be accessed and reused by the scientific community. The datasets are uploaded to ProteomeXchange Consortium via the PRIDE partner repository (http://www.proteomexchange.org) with the dataset identifier PXD012081; PXD012704; PXD015071; PXD015955; or to NCBI Gene Expression Omnibus accessible through GEO Series accession number GSE141891 and GSE141309.

Diabetes is characterized by hyperglycaemia resulted from the impaired ability of the body to produce or respond to insulin. This group of energy metabolism diseases is showing an alarming increase in the incidence rate, the worldwide prevalence being estimated to rise from 2.8% in 2000 to 4.4% in 2030. The two prevailing forms of diabetes are exceedingly difficult to study due to their complex aetiology caused by an intricate genetic/environmental interaction (polygenic and multifactorial). Consequently, their exact causational factors and underlying mechanisms have not yet been defined. Here we propose a novel in vivo approach involving transplanted induced pluripotent stem cells (iPSCs) derived from monogenic diabetes (MODY) types identified in the unique patient collection available at the Norwegian MODY Registry. Upon transplantation into humanized diabetic mice, we will use the outcome of their age-related gradual decay in functionality as a direct in vivo readout signalizing the disorder onset. We will use this setup to address the following questions: What are the cellular processes and conserved molecular pathways characterizing the gradual failure of the iPSC-derived beta-like from MODY patients? Is there a general, potentially age-related mechanism contributing to MODY-iPSC-derived beta-like cell decay? By replying to these questions we will characterize the first dynamic cellular and molecular timeline of beta-cell failure in diabetic disorders, while also defining a general, potentially age-related, onset mechanism. Special emphasis will be given for generation of a short list of novel therapeutic targets for subsequent in vivo testing, which will allow a much more efficient clinical intervention with a greater gain in terms of functionality and healthspan.