Lisa Nivison-Smith

Substrate elasticity provides mechanical signals for the expansion of hemopoietic stem and progenitor cells.

Surprisingly little is known about the effects of the physical microenvironment on hemopoietic stem and progenitor cells. To explore the physical effects of matrix elasticity on well-characterized primitive hemopoietic cells, we made use of a uniquely elastic biomaterial, tropoelastin. Culturing mouse or human hemopoietic cells on a tropoelastin substrate led to a two- to threefold expansion of undifferentiated cells, including progenitors and mouse stem cells. Treatment with cytokines in the presence of tropoelastin had an additive effect on this expansion. These biological effects required substrate elasticity, as neither truncated nor cross-linked tropoelastin reproduced the phenomenon, and inhibition of mechanotransduction abrogated the effects. Our data suggest that substrate elasticity and tensegrity are important mechanisms influencing hemopoietic stem and progenitor cell subsets and could be exploited to facilitate cell culture.

Synthetic human elastin microfibers: Stable cross-linked tropoelastin and cell interactive constructs for tissue engineering applications

Elastin is a key extracellular matrix protein in a range of tissues and a viable candidate for elastic tissue engineering. Elastin is not typically incorporated into engineered scaffolds because of lack of access to pure, homogeneous human elastin. Recombinant human tropoelastin, the monomer precursor of elastin, can be chemically cross-linked to form a polymer and used to generate biomaterials with physical properties similar to native elastin. In this study, we use electrospinning to generate versatile tropoelastin microfibers. Tropoelastin retained structural and biological properties, including secondary structure and coacervation temperature, after fiber formation but was solubilized on exposure to an aqueous environment prior to cross-linking. Two cross-linking methods were utilized to generate synthetic elastin microfibers that were stable in aqueous environments. Microfibers stably persisted for up to 180 days at 37 degrees C. Three primary human cell types derived from elastic tissues were assessed and found to attach and proliferate on both types of microfibers.

Alignment of human vascular smooth muscle cells on parallel electrospun synthetic elastin fibers

We generated parallel elastic fibers from synthetic elastin (SE) as a model of the arterial media and assessed the alignment of smooth muscle cells (SMCs). SE utilized crosslinked electrospun human tropoelastin to form aligned fibers that mimicked the topography and elastin-rich content of the medial extracellular matrix. Bundled parallel fibers were anisotropically more elastic than randomly arranged scaffolds (111 ± 25 kPa vs. 265 ± 17 kPa) in the direction of the fibers. Aligned and random fiber scaffolds each supported SMC growth. Following attachment, SMCs proliferated longitudinally on the parallel fibers and expressed native α-smooth muscle actin.

Retinal amino acid neurochemistry in health and disease.

Advances in basic retinal anatomy, genetics, biochemical pathways and neurochemistry have not only provided a better understanding of retinal function but have also allowed us to link basic science to retinal disease. The link with disease allowed measures to be developed that now provide an opportunity to intervene and slow down or even restore sight in previously ‘untreatable’ retinal diseases. One of the critical advances has been the understanding of the retinal amino acid neurotransmitters, related amino acids, their metabolites and functional receptors. This review provides an overview of amino acid localisation in the retina and examples of how retinal anatomy and amino acid neurochemistry directly links to understanding retinal disease. Also, the implications of retinal remodelling involving amino acid (glutamate) receptors are outlined in this review and insights are presented on how understanding of detrimental and beneficial retinal remodelling will provide better outcomes for patients using strategies for the preservation or restoration of vision. An internet‐based database of retinal images of amino acid labelling patterns and other amino acid‐related images in health and disease is located at http://www.aminoacidimmunoreactivity.com.

Age-related macular degeneration: linking clinical presentation to pathology.

ABSTRACT Age-related macular degeneration (AMD) is one of the leading causes of blindness worldwide in the elderly population. Optometrists, as primary eye health care providers, require the skills and knowledge to accurately diagnose and manage AMD patients. There is an overwhelming body of research related to the clinical presentation, etiology, epidemiology, and pathology of this disease. Additionally, the evolution of new imaging modalities creates new opportunities to clinically detect and analyze previously uncharacterized and earlier changes in the retina. The challenge for optometrists is to combine all this information into an applicable knowledge base for use in everyday clinical assessment of AMD so that timely and accurate referrals can be made to retinal specialists. This review attempts to address this issue by linking the clinical presentation of AMD with the underlying disease biology. We emphasize the contribution of recent noninvasive imaging technologies to the clinical assessment of early and more advanced AMD including optical coherence tomography, fundus autofluorescence, and infrared reflectance.

Using the rd1 mouse to understand functional and anatomical retinal remodelling and treatment implications in retinitis pigmentosa: A review.

Retinitis Pigmentosa (RP) reflects a range of inherited retinal disorders which involve photoreceptor degeneration and retinal pigmented epithelium dysfunction. Despite the multitude of genetic mutations being associated with the RP phenotype, the clinical and functional manifestations of the disease remain the same: nyctalopia, visual field constriction (tunnel vision), photopsias and pigment proliferation. In this review, we describe the typical clinical phenotype of human RP and review the anatomical and functional remodelling which occurs in RP determined from studies in the rd/rd (rd1) mouse. We also review studies that report a slowing down or show an acceleration of retinal degeneration and finally we provide insights on the impact retinal remodelling may have in vision restoration strategies.

Mapping kainate activation of inner neurons in the rat retina

Kainate receptors mediate fast, excitatory synaptic transmission for a range of inner neurons in the mammalian retina. However, allocation of functional kainate receptors to known cell types and their sensitivity remains unresolved. Using the cation channel probe 1‐amino‐4‐guanidobutane agmatine (AGB), we investigated kainate sensitivity of neurochemically identified cell populations within the structurally intact rat retina. Most inner retinal neuron populations responded to kainate in a concentration‐dependent manner. OFF cone bipolar cells demonstrated the highest sensitivity of all inner neurons to kainate. Immunocytochemical localization of AGB and macromolecular markers confirmed that type 2 bipolar cells were part of this kainate‐sensitive population. The majority of amacrine (ACs) and ganglion cells (GCs) showed kainate responses with different sensitivities between major neurochemical classes (γ‐aminobutyric acid [GABA]/glycine ACs > glycine ACs > GABA ACs; glutamate [Glu]/weakly GABA GCs > Glu GCs). Conventional and displaced cholinergic ACs were highly responsive to kainate, whereas dopaminergic ACs do not appear to express functional kainate receptors. These findings further contribute to our understanding of neuronal networks in complex multicellular tissues. J. Comp. Neurol. 521:2416–2438, 2013.

Infrared reflectance imaging in age‐related macular degeneration

The purpose of this article is to describe the appearance of age‐related macular degeneration (AMD) phenotypes using infrared (IR) reflectance imaging. IR reflectance imaging of the retina has the potential to highlight specific sub‐retinal features and pathology. However, its role in macular disease, specifically AMD, is often underestimated and requires clarification.

Vinpocetine regulates cation channel permeability of inner retinal neurons in the ischaemic retina.

Vinpocetine is a natural drug which exerts neuroprotective effects in ischaemia of the brain through actions on cation channels, glutamate receptors and other pathways. This study investigated the effect of vinpocetine on cation channel permeability of inner retinal neurons after acute retinal metabolic insult. We focused on amacrine and ganglion cells immunoreactive for calretinin or parvalbumin due to their previously documented susceptibility to ischaemia. Using the probe, 1-amino-4-guanidobutane (AGB), we observed increased cation channel permeability across amacrine and ganglion cells under ischaemia and hypoglycaemia but not anoxia. Calretinin and parvalbumin immunoreactivity was also reduced during ischaemia and hypoglyacemia but not anoxia. Vinpocetine decreased AGB entry into ischaemic and hypoglycaemic ganglion cells indicating that the drug can modulate unregulated cation entry. In addition, vinpocetine prevented the loss of calretinin and parvalbumin immunoreactivity following ischaemia suggesting it may indirectly regulate intracellular calcium. Vinpocetine also reduced AGB permeability in selected amacrine and ganglion cell populations following N-methyl-D-aspartate (NMDA) but not kainate activation suggesting that vinpocetines regulation of cation channel permeability may partly involve NMDA sensitive glutamate receptors.

Sildenafil alters retinal function in mouse carriers of retinitis pigmentosa.

Sildenafil, the active ingredient in Viagra, has been reported to cause transient visual disturbance from inhibition of phosphodiesterase 6 (PDE6), a key enzyme in the visual phototransduction pathway. This study investigated the effects of sildenafil on the rd1(+/-) mouse, a model for carriers of Retinitis Pigmentosa which exhibit normal vision but may have a lower threshold for cellular stress caused by sildenafil due to a heterozygous mutation in PDE6. Sildenafil caused a dose-dependent decrease in electroretinogram (ERG) responses of normal mice which mostly recovered two days post administration. In contrast, rd1(+/-) mice exhibited a significantly reduced photoreceptor and a supernormal bipolar cell response to sildenafil within 1 h of treatment. Carrier mice retinae took two weeks to return to baseline levels suggesting sildenafil has direct effects on both the inner and outer retina and these effects differ significantly between normal and carrier mice. Anatomically, an increase in expression of the early apoptotic marker, cytochrome C in rd1(+/-) mice indicated that the effects of sildenafil on visual function may lead to degeneration. The results of this study are significant considering approximately 1 in 50 people are likely to be carriers of recessive traits leading to retinal degeneration.