Meghan Hefferon

All Publications

• Juvenile Mice Develop Infarct-Induced Neurodegeneration and Emerging Cognitive Decline in a Model of Pediatric Stroke. Stroke Mayne, E. W., Vanden, K., Hefferon, M. E., Zera, K. A., Buckwalter, M. S. 2026

  Abstract

  Over half of pediatric stroke survivors have permanent cognitive deficits, which can emerge late after stroke. Mechanisms of cognitive decline after pediatric stroke may differ from those in adults because children's strokes occur while brain and immune development are still ongoing. We therefore aimed to develop a pediatric mouse model of infarct-induced delayed cognitive decline to define age-related differences in immune responses compared with adults.Male and female C57BL/6J mice were randomized to stroke or sham surgery at 28 days old to model stroke in late childhood. We used permanent distal middle cerebral artery occlusion followed by 60 minutes of hypoxia to induce an ischemic cortical stroke. Juvenile mice underwent behavioral testing at 1 and 7 weeks after surgery using Barnes maze and Novel Object Recognition tests. We quantified stroke size, atrophy, and neuroinflammation at 3 days and 7 weeks after surgery in juvenile and adult mice using immunostaining.One week after surgery, juvenile stroke and sham mice performed comparably on cognitive testing. However, by 7 weeks after surgery, stroke mice of both sexes performed significantly worse on reversal learning with the Barnes maze. Histologically, juvenile mice had greater innate immune activation at sites of secondary neurodegeneration in the corpus callosum, corticospinal tract, and thalamus at 3 days after stroke, while adults had greater chronic innate immune activity at these sites 7 weeks after stroke.In a model of childhood ischemic stroke, juvenile mice of both sexes developed an emerging cognitive deficit analogous to that seen in pediatric stroke survivors. It was associated with chronic neuroinflammation in uninjured subcortical structures that undergo secondary neurodegeneration. Our results suggest that infarct-induced neurodegeneration occurs after stroke in juvenile mice, and that there are age-related divergent trajectories in the innate immune response to stroke at sites of secondary neurodegeneration.

  View details for DOI 10.1161/STROKEAHA.125.054237

  View details for PubMedID 42220248

• Custom-engineered hydrogels for delivery of human iPSC-derived neurons into the injured cervical spinal cord. Biomaterials Doulames, V. M., Marquardt, L. M., Hefferon, M. E., Baugh, N. J., Suhar, R. A., Wang, A. T., Dubbin, K. R., Weimann, J. M., Palmer, T. D., Plant, G. W., Heilshorn, S. C. 2023; 305: 122400

  Abstract

  Cervical damage is the most prevalent type of spinal cord injury clinically, although few preclinical research studies focus on this anatomical region of injury. Here we present a combinatorial therapy composed of a custom-engineered, injectable hydrogel and human induced pluripotent stem cell (iPSC)-derived deep cortical neurons. The biomimetic hydrogel has a modular design that includes a protein-engineered component to allow customization of the cell-adhesive peptide sequence and a synthetic polymer component to allow customization of the gel mechanical properties. In vitro studies with encapsulated iPSC-neurons were used to select a bespoke hydrogel formulation that maintains cell viability and promotes neurite extension. Following injection into the injured cervical spinal cord in a rat contusion model, the hydrogel biodegraded over six weeks without causing any adverse reaction. Compared to cell delivery using saline, the hydrogel significantly improved the reproducibility of cell transplantation and integration into the host tissue. Across three metrics of animal behavior, this combinatorial therapy significantly improved sensorimotor function by six weeks post transplantation. Taken together, these findings demonstrate that design of a combinatorial therapy that includes a gel customized for a specific fate-restricted cell type can induce regeneration in the injured cervical spinal cord.

  View details for DOI 10.1016/j.biomaterials.2023.122400

  View details for PubMedID 38134472

• Cell Microencapsulation Within Engineered Hyaluronan Elastin-Like Protein (HELP) Hydrogels. Current protocols Hefferon, M. E., Huang, M. S., Liu, Y., Navarro, R. S., de Paiva Narciso, N., Zhang, D., Aviles-Rodriguez, G., Heilshorn, S. C. 2023; 3 (11): e917

  Abstract

  Three-dimensional cell encapsulation has rendered itself a staple in the tissue engineering field. Using recombinantly engineered, biopolymer-based hydrogels to encapsulate cells is especially promising due to the enhanced control and tunability it affords. Here, we describe in detail the synthesis of our hyaluronan (i.e., hyaluronic acid) and elastin-like protein (HELP) hydrogel system. In addition to validating the efficacy of our synthetic process, we also demonstrate the modularity of the HELP system. Finally, we show that cells can be encapsulated within HELP gels over a range of stiffnesses, exhibit strong viability, and respond to stiffness cues. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Elastin-like protein modification with hydrazine Basic Protocol 2: Nuclear magnetic resonance quantification of elastin-like protein modification with hydrazine Basic Protocol 3: Hyaluronic acid-benzaldehyde synthesis Basic Protocol 4: Nuclear magnetic resonance quantification of hyaluronic acid-benzaldehyde Basic Protocol 5: 3D cell encapsulation in hyaluronan elastin-like protein gels.

  View details for DOI 10.1002/cpz1.917

  View details for PubMedID 37929691

• Hyaluronan and elastin-like protein (HELP) gels significantly improve microsphere retention in the myocardium. Biomaterials science Suhar, R. A., Doulames, V. M., Liu, Y., Hefferon, M. E., Figueroa, O. 3., Buabbas, H., Heilshorn, S. C. 2022

  Abstract

  Heart disease is the leading cause of death globally, and delivery of therapeutic cargo (e.g., particles loaded with proteins, drugs, or genes and cells) through direct injection into the myocardium is a promising clinical intervention. However, retention of deliverables to the contracting myocardium is low, with as much as 60-90% of payload being lost within 24 hr. Commercially-available injectable hydrogels, including Matrigel, have been hypothesized to increase payload retention but have not yielded significant improvements in quantified analyses. Here, we assess a recombinant hydrogel composed of chemically modified hyaluronan and elastin-like protein (HELP) as an alternative injectable carrier to increase cargo retention. HELP is crosslinked using dynamic covalent bonds, and tuning the hyaluronan chemistry significantly alters hydrogel mechanical properties including stiffness, stress relaxation rate, and ease of injectability through a needle or catheter. These materials can be injected even after complete crosslinking, extending the time window for surgical delivery. We show that HELP gels significantly improve in vivo retention of microsphere cargo compared to Matrigel, both 1 day and 7 days post-injection directly into the rat myocardium. These data suggest that HELP gels may assist with the clinical translation of therapeutic cargo designed for delivery into the contracting myocardium by preventing acute cargo loss.

  View details for DOI 10.1039/d1bm01890f

  View details for PubMedID 35411353