The SSBP3 co-regulator is required for glucose homeostasis, pancreatic islet architecture, and beta-cell identity.

OBJECTIVE: Transcriptional complex activity drives the development and function of pancreatic islet cells to allow for proper glucose regulation. Prior studies from our lab and others highlighted that the LIM-homeodomain transcription factor (TF), Islet-1 (Isl1), and its interacting co-regulator, Ldb1, are vital effectors of developing and adult ß-cells. We further found that a member of the Single Stranded DNA-Binding Protein (SSBP) co-regulator family, SSBP3, interacts with Isl1 and Ldb1 in ß-cells and primary islets (mouse and human) to impact ß-cell target genes MafA and Glp1R in vitro. Members of the SSBP family stabilize TF complexes by binding directly to Ldb1 and protecting the complex from ubiquitin-mediated turnover. In this study, we hypothesized that SSBP3 has critical roles in pancreatic islet cell function in vivo, similar to the Isl1::Ldb1 complex. METHODS: We first developed a novel SSBP3 LoxP allele mouse line, where Cre-mediated recombination imparts a predicted early protein termination. We bred this mouse with constitutive Cre lines (Pdx1- and Pax6-driven) to recombine SSBP3 in the developing pancreas and islet (SSBP3ΔPanc and SSBP3ΔIslet), respectively. We assessed glucose tolerance and used immunofluorescence to detect changes in islet cell abundance and markers of ß-cell identity and function. Using an inducible Cre system, we also deleted SSBP3 in the adult ß-cell, a model termed SSBP3Δß-cell. We measured glucose tolerance as well as glucose-stimulated insulin secretion (GSIS), both in vivo and in isolated islets in vitro. Using islets from control and SSBP3Δß-cell we conducted RNA-Seq and compared our results to published datasets for similar ß-cell specific Ldb1 and Isl1 knockouts to identify commonly regulated target genes. RESULTS: SSBP3ΔPanc and SSBP3ΔIslet neonates present with hyperglycemia. SSBP3ΔIslet mice are glucose intolerant by P21 and exhibit a reduction of ß-cell maturity markers MafA, Pdx1, and UCN3. We observe disruptions in islet cell architecture with an increase in glucagon+ α-cells and ghrelin+ ε-cells at P10. Inducible loss of ß-cell SSBP3 in SSBP3Δß-cell causes hyperglycemia, glucose intolerance, and reduced GSIS. Transcriptomic analysis of 14-week-old SSBP3Δß-cell islets revealed a decrease in ß-cell function gene expression (Ins, MafA, Ucn3), increased stress and dedifferentiation markers (Neurogenin-3, Aldh1a3, Gastrin), and shared differentially expressed genes between SSBP3, Ldb1, and Isl1 in adult ß-cells. CONCLUSIONS: SSBP3 drives proper islet identity and function, where its loss causes altered islet-cell abundance and glucose homeostasis. ß-Cell SSBP3 is required for GSIS and glucose homeostasis, at least partially through shared regulation of Ldb1 and Isl1 target genes.

International study of 24-h movement behaviors of early years (SUNRISE): a pilot study from Bangladesh.

BACKGROUND: The World Health Organization (WHO) released guidelines for physical activity, sedentary behavior, and sleep for children under 5 years of age in 2019. In response to these guidelines, this pilot study aimed to (i) determine the proportion of preschool children (ages 3-4 years) who met the WHO guidelines; (ii) examine the feasibility of the proposed protocol for the SUNRISE study; and (iii) assess the impact of the COVID-19 pandemic on movement behaviors of preschool children in Bangladesh. METHODS: Time spent in physical activity, sedentary behavior and sleep were objectively measured using two types of accelerometers (ActiGraph wGT3x-BT and ActivPAL4). Screen time and sleep quality were assessed via parent questionnaire. Fine and gross motor skills were measured using the Ages and Stages Questionnaire (3rd edition). Three executive functions were assessed using the Early Years Toolbox. Focus groups were conducted with parents and childcare staff to determine the feasibility of the protocol. Follow-up data during COVID-19 pandemic was collected from parents over phone. RESULTS: Data from 63 preschool-aged children and their parents was analyzed in this pilot study. Only three children (4.7%) met all components of the WHO guidelines. Separately, children meeting physical activity, sedentary screen time and sleep guidelines were 71.9%, 17.5%, and 59.7% respectively. The proportion of all children who were developmentally on-track for the gross and fine motor skills was 58.7% and 50.8%, respectively. Parents and educators reported that the protocol was feasible except for the activPAL-4 accelerometer. Approximately, 39% of children (14 out of 37) who wore this device developed itchy skin and rashes resulting in the suspension of using this device mid-way through data collection. During COVID-19, there was a significant decrease in children's total physical activity (- 193 min/day), and time spent outside on weekdays (- 75 min/day) and weekend days (- 131 min/day) and a significant increase in sedentary screen time (+85 min/day). CONCLUSION: Only a low proportion of children met the WHO guidelines. Methods and devices (except ActivPAL4) used in this pilot study proved to be feasible and this has paved the way to conduct the main SUNRISE study in Bangladesh. Future measures should be taken to address the issue of movement behaviors of children during the time of pandemics like COVID-19.