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Mammalian central nervous system has a limited ability for self-repair under diseased or injury conditions. Repair strategies focused on exogenously delivering autologous neural stem cells (NSCs) to replace lost neuronal populations and axonal pathways in situ, and promote endogenous repair mechanisms are gaining traction. Successful outcomes are contingent on selecting an appropriate delivery vehicle for injecting cells that promotes cell retention and survival, elicits differentiation to desired lineages, and enhances axonal outgrowth upon integration into the host tissue. Hydrogels made of varying compositions of collagen, laminin, hyaluronic acid (HA), and chondroitin sulfate proteoglycan (CSPG) were developed, with no external crosslinking agents, to mimic the native extracellular matrix composition. The physical (porosity, pore-size, gel integrity, swelling ratio, and enzymatic degradation), mechanical (viscosity, storage and loss moduli, Young's modulus, creep, and stress-relaxation), and biological (cell survival, differentiation, neurite outgrowth, and integrin expression) characteristics of these hydrogels were assessed. These hydrogels exhibited excellent injectability, retained gel integrity, and matched the mechanical moduli of native brain tissue, possibly due to natural collagen fibril polymerization and physical-crosslinking between HA molecules and collagen fibrils. Depending on the composition, these hydrogels promoted cell survival, neural differentiation, and neurite outgrowth, as evident from immunostaining and western blots. These cellular outcomes were facilitated by cellular binding via α

The microtubule associated protein tau plays a critical role in the pathogenesis of neurodegenerative disease. Recent studies suggest that tau also plays a role in disorders of neuronal connectivity, including epilepsy and post-traumatic stress disorder. Animal studies have shown that the MAPT gene, which codes for the tau protein, undergoes complex pre-mRNA alternative splicing to produce multiple isoforms during brain development. Human data, particularly on temporal and regional variation in tau splicing during development are however lacking. In this study, we present the first detailed examination of the temporal and regional sequence of MAPT alternative splicing in the developing human brain. We used a novel computational analysis of large transcriptomic datasets (total n = 502 patients), quantitative polymerase chain reaction (qPCR) and western blotting to examine tau expression and splicing in post-mortem human fetal, pediatric and adult brains. We found that MAPT exons 2 and 10 undergo abrupt shifts in expression during the perinatal period that are unique in the canonical human microtubule-associated protein family, while exon 3 showed small but significant temporal variation. Tau isoform expression may be a marker of neuronal maturation, temporally correlated with the onset of axonal growth. Immature brain regions such as the ganglionic eminence and rhombic lip had very low tau expression, but within more mature regions, there was little variation in tau expression or splicing. We thus demonstrate an abrupt, evolutionarily conserved shift in tau isoform expression during the human perinatal period that may be due to tau expression in maturing neurons. Alternative splicing of the MAPT pre-mRNA may play a vital role in normal brain development across multiple species and provides a basis for future investigations into the developmental and pathological functions of the tau protein.

A major onset of heart failure is myocardial infarction, which causes the myocardium to lose cardiomyocytes and transform into a scar tissue. Since mammalian infarcted cardiac tissue has a limited ability to regenerate, alternative strategies including implantation of tissue-engineered scaffolds at the site of damaged myocardium have been explored. The goal is to enable in situ cardiac reconstruction at the injured myocardium site, replace the lost cardiomyocytes, deliver the required biomolecules, and remodel the extracellular matrix (ECM). ECM synthesis and deposition by cardiomyocytes within such scaffolds remains categorically unexplored. Here, we investigated the survival, ECM synthesis and deposition, and matrix metalloproteinases (MMPs) release by cardiomyocytes within three-dimensional (3D) substrates. Rat cardiomyocytes were cultured for three weeks within two structurally different substrates: 3D collagen hydrogels or polycaprolactone (PCL) nanofibrous scaffolds. The concentration and composition of the hydrogels was varied, while PCL nanofibers were surface-modified with various ECM proteins. Results showed that myocyte attachment and survival was higher within collagen hydrogels, while myocyte alignment and beating was noted only within PCL scaffolds. Total protein synthesis by myocytes within PCL scaffolds was significantly higher compared to that within collagen hydrogels, although more protein was deposited as matrix within hydrogels. Significant ECM synthesis and matrix deposition, TIMP-1, and MMP release were noted within modified collagen hydrogels and PCL nanofiber scaffolds. These results were qualitatively confirmed by imaging techniques. Results attest to the prominent role of scaffold composition and architecture in influencing cardiomyocyte phenotype, matrix synthesis and cytokines release, with significant applications in cardiac tissue remodeling strategies.

Tissue Engineering Approaches for Motor Neuron Pathway Regeneration During fetal development, a tightly-regulated spatio-temporal pattern of guidance cues directs and maintains motor neuron axonal growth along specific pathways to reach the target cells and tissues. However, an inflammatory environment resulting from an injury (e.g., trauma, stroke) or disease [e.g., amyotrophic lateral sclerosis (ALS), primary lateral sclerosis (PLS), and hereditary spastic paraplegia (HSP)] leads to progressive degeneration of motor neurons and destruction of axonal tracts in the adult CNS.