Divergent immune responses to synthetic and biological scaffolds.

The immune system plays a critical role in wound healing and the response to biomaterials. Biomaterials-directed regenerative immunology is an immunoengineering strategy that targets the immune system to promote tissue repair. Biomaterial scaffolds employed in regenerative medicine can be broadly classified as biological (such as those derived from the tissue extracellular matrix) or synthetic. Here, we show in depth the divergent myeloid response to biological versus synthetic biomaterial scaffolds. While neutrophil depletion and changes in physical properties such as shape and mechanics can modulate the pro-inflammatory myeloid immune response to synthetic materials to a degree, the overall general divergent myeloid responses persist. Biologic scaffolds elicit a type-2-like immune response with upregulation of genes such as Il4, Cd163, Mrc1 and Chil3, as well as genes associated with damage-associated molecular patterns providing another possible mechanism by which ECM scaffolds promote wound healing via amplification of endogenous wound-associated signaling pathways. Synthetic materials recruit a high proportion of neutrophils which is compounded by material stiffness and by the presence of an injury. Understanding the complex immune response to biomaterial classes will help in the efficient design of immunoengineering strategies and optimizing regenerative and reducing foreign body fibrotic responses to scaffolds.

HuR and GRSF1 modulate the nuclear export and mitochondrial localization of the lncRNA RMRP.

Some mitochondrial long noncoding RNAs (lncRNAs) are encoded by nuclear DNA, but the mechanisms that mediate their transport to mitochondria are poorly characterized. Using affinity RNA pull-down followed by mass spectrometry analysis, we found two RNA-binding proteins (RBPs), HuR (human antigen R) and GRSF1 (G-rich RNA sequence-binding factor 1), that associated with the nuclear DNA-encoded lncRNA RMRP and mobilized it to mitochondria. In cultured human cells, HuR bound RMRP in the nucleus and mediated its CRM1 (chromosome region maintenance 1)-dependent export to the cytosol. After RMRP was imported into mitochondria, GRSF1 bound RMRP and increased its abundance in the matrix. Loss of GRSF1 lowered the mitochondrial levels of RMRP, in turn suppressing oxygen consumption rates and modestly reducing mitochondrial DNA replication priming. Our findings indicate that RBPs HuR and GRSF1 govern the cytoplasmic and mitochondrial localization of the lncRNA RMRP, which is encoded by nuclear DNA but has key functions in mitochondria.

Induction of VEGFA mRNA translation by CoCl2 mediated by HuR.

Vascular endothelial growth factor (VEGF) A is a master regulator of neovascularization and angiogenesis. VEGFA is potently induced by hypoxia and by pathological conditions including diabetic retinopathy and tumorigenesis. Fine-tuning of VEGFA expression by different stimuli is important for maintaining tissue vascularization and organ homeostasis. Here, we tested the effect of the hypoxia mimetic cobalt chloride (CoCl2) on VEGFA expression in human cervical carcinoma HeLa cells. We found that CoCl2 increased the levels of VEGFA mRNA and VEGFA protein without affecting VEGFA mRNA stability. Biotin pulldown analysis to capture the RNA-binding proteins (RBPs) bound to VEGFA mRNA followed by mass spectrometry analysis revealed that the RBP HuR [human antigen R, a member of the embryonic lethal abnormal vision (ELAV) family of proteins], interacts with VEGFA mRNA. VEGFA mRNA-tagging experiments showed that exposure to CoCl2 increases the interaction of HuR with VEGFA mRNA and promoted the colocalization of HuR and the distal part of the VEGFA 3'-untranslated region (UTR) in the cytoplasm. We propose that under hypoxia-like conditions, HuR enhances VEGFA mRNA translation.