Understanding the role of sialylation in MSC survival and behavior

The use of mesenchymal stromal cells (MSCs) has emerged as a promising therapeutic strategy to treat a variety of immune-mediated diseases, however, many clinical trials have failed to live up to the high expectations raised by encouraging preclinical data. This can be attributed to the inability of administered MSCs to target specific tissues, or survive long enough to promote therapeutic benefit. Recent reports have highlighted that N-linked glycans (N-glycans) may play a key role in MSC migration and survival, and are therefore a novel approach to current hurdles in MSC-based therapies.

Many studies within the field of oncology have linked sialic acid, a terminal glycan constituent, to increased cancer cell metastasis chemoresistance. Therefore, it is hypothesized that sialylation plays a key role in MSC migration and survival. This study aims to elucidate the role of sialic acid in MSCs, through an exploration of how culture conditions or added factors can be used to selectively alter surface sialylation, as well as exploring how directly inhibiting or upregulating sialylation effects MSC behavior. Cell surface sialylations can be measured using flow cytometry with a carbohydrate-binding protein (SNA) which has a specific affinity for sialic acid groups. This SNA lectin is conjugated to a FITC fluorophore, so sialylations can be detected as a proportional fluorescent readout. Expression of genes which are regulated by factors altering sialylations can be measured through RT-PCR to better understand the molecular mechanisms which govern sialylation.

Preliminary results show that preconditioning MSCs with an inhibitor of sialic acid, P-3FAX-Neu5Ac, promotes cell survival within an in vitro ischemia model. We have also found that MSCs increase their surface sialylations in response to treatment with the pro-inflammatory cytokine, IFN-γ, as well as being cultured in low serum media or plated at a high density. RT-PCR results show that these conditions increase cell sialylations through transcriptional regulation of different sialyltransferases, the enzymes responsible for adding sialic acid on to the glycan terminus (ST3Gal1 and ST6Gal1). Taken together, our results support the notion that sialylation may play a key role in MSC survival and behavior, however further work will be necessary to confirm these findings. This study highlights clinically relevant strategies for manipulating sialylations without the need for genetically modifying the cells, and is therefore a safe approach to inform MSC-based therapies for the improvement of cell retention and delivery.