Differential expression of receptors mediating receptor-mediated transcytosis (RMT) in brain microvessels, brain parenchyma and peripheral tissues of the mouse and the human

Receptor-mediated transcytosis (RMT) is a principal pathway for transport of macromolecules essential for brain function across the blood–brain barrier (BBB). Antibodies or peptide ligands which bind RMT receptors are often co-opted for brain delivery of biotherapeutics. Constitutively recycling transferrin receptor (TfR) is a prototype receptor utilized to shuttle therapeutic cargos across the BBB. Several other BBB-expressed receptors have been shown to mediate transcytosis of antibodies or protein ligands including insulin receptor (INSR) and insulin-like growth factor-1 receptor (IGF1R), lipid transporters LRP1, LDLR, LRP8 and TMEM30A, solute carrier family transporter SLC3A2/CD98hc and leptin receptor (LEPR). In this study, we analyzed expression patterns of genes encoding RMT receptors in isolated brain microvessels, brain parenchyma and peripheral organs of the mouse and the human using RNA-seq approach. IGF1R, INSR and LRP8 were highly enriched in mouse brain microvessels compared to peripheral tissues. In human brain microvessels only INSR was enriched compared to either the brain or the lung. The expression levels of SLC2A1, LRP1, IGF1R, LRP8 and TFRC were significantly higher in the mouse compared to human brain microvessels. The protein expression of these receptors analyzed by Western blot and immunofluorescent staining of the brain microvessels correlated with their transcript abundance. This study provides a molecular transcriptomics map of key RMT receptors in mouse and human brain microvessels and peripheral tissues, important to translational studies of biodistribution, efficacy and safety of antibodies developed against these receptors.

A comparative analysis of the structural, functional and biological differences between Mouse and Human Nerve Growth Factor

NGF is the prototype member of the neurotrophin family of proteins that promote the survival and growth of selected neurons in the central and peripheral nervous systems. As for all neurotrophins, NGF is translated as a pre-pro-protein. Over the years, NGF and proNGF of either human or mouse origin, given their high degree of homology, have been exploited for numerous applications in biomedical sciences. The mouse NGF has been considered the golden-standard for bioactivity. Indeed, due to evolutionary relatedness to human NGF and to its ready availability and by assuming identical properties to its human counterpart, the mouse NGF, isolated and purified from sub-maxillary glands, has been tested not only in laboratory practice and in preclinical models, but it has also been evaluated in several human clinical trials. Aiming to validate this assumption, widely believed, we performed a comparative study of the biochemical and biophysical properties of the mouse and human counterparts of NGF and proNGF. The mature and the precursor proteins of either species strikingly differ in their biophysical profiles and, when tested for ligand binding to their receptors, in their in vitro biological activities. We provide a structural rationale that accounts for their different functional behaviors. Despite being highly conserved during evolution, NGF and proNGF of mouse and human origins show distinct properties and therefore special care must be taken in performing experiments with cross-species systems in the laboratory practice, in developing immunoassays, in clinical trials and in pharmacological treatments.