Probing the potential of mucus permeability to signify preterm birth risk

Preterm birth is the leading cause of neonatal mortality, and is frequently associated with intra-amniotic infection hypothesized to arise from bacterial ascension across a dysfunctional cervical mucus plug. To study this dysfunction, we assessed the permeability of cervical mucus from non-pregnant ovulating (n = 20) and high-(n = 9) and low-risk (n = 16) pregnant women to probes of varying sizes and surface chemistries. We found that the motion of negatively charged, carboxylated microspheres in mucus from pregnant patients was significantly restricted compared to ovulating patients, but not significantly different between high-A nd low-risk pregnant women. In contrast, charged peptide probes small enough to avoid steric interactions, but sensitive to the biochemical modifications of mucus components exhibited significantly different transport profiles through mucus from high-A nd low-risk patients. Thus, although both microstructural rearrangements of the components of mucus as well as biochemical modifications to their adhesiveness may alter the overall permeability of the cervical mucus plug, our findings suggest that the latter mechanism plays a dominant role in the impairment of the function of this barrier during preterm birth. We expect that these probes may be readily adapted to study the mechanisms underlying disease progression on all mucosal epithelia, including those in the mouth, lungs, and gut.National Science Foundation (U.S.) (Award DMR-0819762)National Science Foundation (U.S.) (Award 1122374

Understanding the selective permeability of biological hydrogels

Thesis: Ph. D., Massachusetts Institute of Technology, Computational and Systems Biology Program, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 148-160).Biological hydrogels are fundamental to life, from microbial biofilms to mucus and the nuclear pore in humans. These hydrogels exhibit complex selective permeability behavior, allowing the passage of some particles while blocking the penetration of others. This selective permeability is critical for understanding the biological and medicinal impact of mucus, which coats all non-keratinized epithelia in the body. Mucus controls the penetration of microbes, pollutants, and nanoparticles through a combination of steric and interactive (binding-based) constraints. For small molecules, binding to mucus and in particular mucin, the main gel-forming component of mucus, affects diffusive permeability and may also affect a molecule's biological or therapeutic activity. However, the molecular characteristics leading to mucus binding are not well understood.I therefore developed a mucus binding assay with substantially greater throughput than any existing assay, and combined it with a mucin binding screen to identify a new motif as associated with binding to mucin. I also validate the link between binding to mucin and reduced activity in mucin for the antibiotic colistin. Next, I applied my binding technique to study the binding of a wide range of antibiotics and inhaled drugs to respiratory mucus, and identified previously unknown mucus binding interactions. These binding interactions could impact the activity of the drugs within the mucus or impact their lung residence time in the case of highly muco-obstructive lung diseases. The nuclear pore, which controls the passage of material between the nucleus and the cytoplasm, is similar to mucus in that it too is a selectively permeable network of disordered proteins.Passage through the nuclear pore requires interaction with the network that was initially thought to be purely hydrophobic in character. However, there is evidence that electrostatic interactions also partly govern nuclear pore transport. Here, we apply a peptide-based system to study the interplay of hydrophobic and electrostatic interactions to further dissect the biochemistry underlying nuclear pore function.by Jacob Julian Seid Witten.Ph. D.Ph.D. Massachusetts Institute of Technology, Computational and Systems Biology Progra

The particle in the spider's web: transport through biological hydrogels

Biological hydrogels such as mucus, extracellular matrix, biofilms, and the nuclear pore have diverse functions and compositions, but all act as selectively permeable barriers to the diffusion of particles. Each barrier has a crosslinked polymeric mesh that blocks penetration of large particles such as pathogens, nanotherapeutics, or macromolecules. These polymeric meshes also employ interactive filtering, in which affinity between solutes and the gel matrix controls permeability. Interactive filtering affects the transport of particles of all sizes including peptides, antibiotics, and nanoparticles and in many cases this filtering can be described in terms of the effects of charge and hydrophobicity. The concepts described in this review can guide strategies to exploit or overcome gel barriers, particularly for applications in diagnostics, pharmacology, biomaterials, and drug delivery.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DMR – 0819762)National Science Foundation (U.S.) (NSF R01 R01-EB017755)National Science Foundation (U.S.) (NSF Career PHY-1454673)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374