Environmental oxygen affects ex vivo growth and proliferation of mesenchymal progenitors by modulating mitogen-activated protein kinase and mammalian target of rapamycin signaling.

BACKGROUND AIMS: Stem and progenitor cells of hematopoietic and mesenchymal lineages reside in the bone marrow under low oxygen (O2) saturation. O2 levels used in ex vivo expansion of multipotent mesenchymal stromal cells (MSCs) affect proliferation, metabolism and differentiation. METHODS: Using cell-based assays and transcriptome and proteome data, the authors compared MSC cultures simultaneously grown under a conventional 19.95% O2 atmosphere or at 5% O2. RESULTS: In 5% O2, MSCs showed better proliferation and higher self-renewal ability, most probably sustained by enhanced signaling activity of mitogen-activated protein kinase and mammalian target of rapamycin pathways. Non-oxidative glycolysis-based energy metabolism supported growth and proliferation in 5% O2 cultures, whereas MSCs grown under 19.95% O2 also utilized oxidative phosphorylation. Cytoprotection mechanisms used by cells under 5% O2 differed from 19.95% O2  suggesting differences in the triggers of cell stress between these two O2  conditions. CONCLUSIONS: Based on the potential benefits for the growth and metabolism of MSCs, the authors propose the use of 5% O2 for MSC culture.

Red-shifted backbone N-H photocaging agents.

Light is a uniquely powerful tool for spatiotemporal control of molecular structure, necessitating the development of new photocaging approaches. This communication describes the design, synthesis, and reactivity of two new photoreactive boronic acid reagents for backbone N-H modification and subsequent photocleavage.

A Cell-Permeant Nanobody-Based Degrader That Induces Fetal Hemoglobin.

Proximity-based strategies to degrade proteins have enormous therapeutic potential in medicine, but the technologies are limited to proteins for which small molecule ligands exist. The identification of such ligands for therapeutically relevant but "undruggable" proteins remains challenging. Herein, we employed yeast surface display of synthetic nanobodies to identify a protein ligand selective for BCL11A, a critical repressor of fetal globin gene transcription. Fusion of the nanobody to a cell-permeant miniature protein and an E3 adaptor creates a degrader that depletes cellular BCL11A in differentiated primary erythroid precursor cells, thereby inducing the expression of fetal hemoglobin, a modifier of clinical severity of sickle cell disease and ß-thalassemia. Our strategy provides a means of fetal hemoglobin induction through reversible, temporal modulation of BCL11A. Additionally, it establishes a new paradigm for the targeted degradation of previously intractable proteins.