Biology subjects

Sommer, L.

Publications and source records attributed to Sommer, L..

3 recordsLinked to original sources

bioRxiv2025

HydroMEA: A 3D Hydrogel Based Microfluidic Device to Study Electrophysiology for Myelinated Nerve-on-Chip

Engineered in vitro platforms are powerful systems to study information flow in the nervous system. While existing polydimethylsiloxane (PDMS)-based microfluidic platforms offer precise architectures, the cultured neurons grow on two-dimensional (2D) planar multielectrode arrays (MEA). To mimic the native microenvironment, where neurons grow in three-dimensional (3D) extracellular matrices (ECM), 3D hydrogels can be designed to encapsulate cells and enable physiologically-mimicked behaviors. Here, we describe hydroMEA, a 3D platform fabricated by placing PDMS microstructures on a high-density MEA and filled with a desired hydrogel, to offer controlled topologies, physiologically-relevant microenvironments, and real-time electrophysiological measurements. First, we developed a gelatin methacryloyl (GelMA) hydrogel with incorporated ECM components and tuned the mechanical properties to match those of nerve tissue. The hydrogel was able to support: 1) the growth of iPSC-derived sensory neurons (hSNs) for >100 days; 2) co-cultures of hSN with human embryonic stem cell-derived Schwann cells (hSCs), to enable reliable 3D myelination. Next, hydroMEA were prepared for topologically- defined 3D growth and myelination in designated compartments. Finally, electrophysiological evaluation of hSN-hSCs co-cultures revealed increased conduction speeds indicating functional myelin. This platform is a promising tool to study cell-cell interactions and to functionally evaluate the effect of pharmacological compounds in a more translational manner.

bioengineering↗

bioRxiv2024

Impaired erythroid maturation in murine embryos upon loss of the preeclampsia-associated serine protease prostasin

In humans, the membrane-bound serine protease prostasin encoded by Prss8 is associated with preeclampsia, a gestational hypertension disorder affecting blood supply of the placenta. Mice deficient in Prss8 resulted in the death of embryos at embryonic day (E) 14.5 and it was characterized by impaired placental labyrinth maturation and vascularization. A pale phenotype was observed in these embryos, suggesting ineffective erythropoiesis. Thus, in this study we analyzed this phenotype further in Prss8-/- embryos at E11.5 and E12.5. We found a reduced number of fetal erythroblasts in placenta, yolk sac and fetal liver of Prss8-/- embryos, while the reticulocyte number was increased, suggesting a defective terminal erythroid differentiation. Further, single-cell RNA sequencing (scRNA-seq) analyses of aorta-gonad-mesonephros (AGM) revealed an upregulation of several ribosomal genes associated with Diamond-Blackfan anemia in erythroid cells of Prss8-/- (KO) embryos. These cells showed a lower capacity to maturate into erythrocytes in vivo and in vitro, despite hematopoietic cells (HSCs) being produced normally. We suggested prostasin influenced erythropoiesis in a cell-extrinsic manner, since Prss8 expression was not detected in erythroid cells but highly expressed in ectoderm-like cells within the AGM. Congruently, while yolk sac-derived cells displayed no erythroid maturation defect in vitro, the yolk sac vascular remodeling in KO embryos was impaired as evidenced by reduced secondary branching likely as a consequence of the reduced blood flow. Our findings unveiled a novel role for this serine protease in terminal maturation of erythrocytes in the fetal liver and open new research avenues for understanding the physiological mechanism of prostasin and its pathological implications. Key PointsO_LIPrss8 deficiency causes transcriptional changes in erythroid progenitor cells in the AGM leading to impaired embryonic erythropoiesis C_LIO_LIOverexpression of Rpl and Rps genes by erythroid cells lacking Prss8 leads to defective erythropoiesis and embryonic lethality C_LI

developmental biology↗

bioRxiv2023

Extracellular sodium regulates fibroblast growth factor 23 (FGF23) formation.

Fibroblast growth factor-23 (FGF23) is a bone-derived hormone that has recently received much attention due to its association with the progression of chronic kidney disease, cardiovascular disease, and associated mortality. Extracellular sodium concentration ([Na+]) plays a significant role in bone metabolism. Hyponatremia (low serum [Na+]) has recently been shown to be independently associated with FGF23 levels in patients with chronic systolic heart failure. However, nothing is known about the direct impact of [Na+] on FGF23 production. Here, we show that an elevated [Na+] (+20 mM) suppressed FGF23 formation, whereas low [Na+] (-20 mM) increased FGF23 synthesis in the osteoblast-like cell line UMR-106. Similar bidirectional changes in FGF23 abundance were observed when osmolality was altered by mannitol but not by urea, suggesting a role of tonicity in FGF23 formation. Moreover, these changes in FGF23 were inversely proportional to the expression of NFAT5 (nuclear factor of activated T cells-5), a transcription factor responsible for tonicity-mediated cellular adaptations. On the other hand, arginine vasopressin (AVP), which is often responsible for hyponatremia, did not affect FGF23 production. Next, comprehensive and unbiased RNA-seq analysis of UMR-106 cells exposed to low vs. high [Na+] revealed several novel genes involved in cellular adaptation to altered tonicity. Additional analysis of cells with Crisp-Cas9 mediated NFAT5 deletion indicated that NFAT5 controls numerous genes associated with FGF23 synthesis, thereby confirming its role in [Na+]-mediated FGF23 regulation. In line with these in vitro observations, we found that human hyponatremia patients have higher FGF23 levels. Our results suggest that [Na+] is a critical regulator of FGF23 synthesis. SIGNIFICANCE STATEMENTFibroblast growth factor 23 (FGF23) is a bone-derived hormone that controls phosphate and vitamin D metabolism. Excess FGF23 is postulated to cause left ventricular hypertrophy, while FGF23 deficiency reduces life span and mimics age-related diseases in mice. FGF23 is also a potential biomarker for chronic kidney disease and cardiovascular disorders, but its role in disease progression is unclear. Therefore, it is important to explore the regulation of FGF23 production, which is incompletely understood. Our paper identifies extracellular-sodium-NFAT5 signaling as a key regulator of FGF23 formation.

physiology↗