Protamine/DNA/Niosome Ternary Nonviral Vectors for Gene Delivery to the Retina: The Role of Protamine

The present study aimed to evaluate the incorporation of protamine into niosome/DNA vectors to analyze the potential application of this novel ternary formulation to deliver the pCMS-EGFP plasmid into the rat retina. Binary vectors based on niosome/DNA and ternary vectors based on protamine/DNA/niosomes were prepared and physicochemically characterized. In vitro experiments were performed in ARPE-19 cells. At 1:1:5 protamine/DNA/niosome mass ratio, the resulted ternary vectors had 150 nm size, positive charge, spherical morphology, and condensed, released, and protected the DNA against enzymatic digestion. The presence of protamine in the ternary vectors improved transfection efficiency, cell viability, and DNA condensation. After ocular administration, the EGFP expression was detected in different cell layers of the retina depending on the administration route without any sign of toxicity associated with the formulations. While subretinal administration transfected mainly photoreceptors and retinal pigment epithelial cells at the site of injection, intravitreal administration produced a more uniform distribution of the protein expression through the inner layers of the retina. The protein expression in the retina persisted for at least one month after both administrations. Our study highlights the flattering properties of protamine/DNA/niosome ternary vectors for efficient and safe gene delivery to the rat retina.

A novel cationic niosome formulation for gene delivery to the retina

Niosomes represent a recent promising approach for gene delivery purposes. We elaborated on a novel niosome formulation based on the 2,3-di(tetradecyloxy)propan-1-amine cationic lipid, combined with squalene and polysorbate 80 to evaluate the transfection efficiency in rat retinas. Niosomes prepared by the solvent emulsification-evaporation technique were mixed with the pCMSEGFP plasmid to form lipoplexes which were characterized in terms of morphology, size, surface charge, and DNA condensation, protection and release. In vitro studies were conducted to evaluate transfection efficiency, viability and internalization mechanism in HEK-293 and ARPE-19 cells. The efficacy of the most promising formulation was evaluated in rat eyes by monitoring the expression of the EGFP after intravitreal and subretinal injections. Lipoplexes at 15/1 ratio were 200nm in size, 25mV in zeta potential and exhibited spherical morphology. At this ratio, niosomes condensed and protected the DNA from enzymatic digestion. Lipoplexes successfully transfected HEK-293 and specially ARPE-19 cells, without affecting the viability. Whereas lipoplexes entered mainly retinal cells by clathrin-mediated endocytosis, HEK-293 cells showed a higher caveolae-dependent entry. After ocular administration, the expression of EGFP was detected in different cells of the retina depending on the administration route. This novel niosome formulation represents a promising approach to deliver genetic material into the retina to treat inherited retinal diseases.

Number and spatial distribution of intrinsically photosensitive retinal ganglion cells in the adult albino rat

Intrinsically photosensitive retinal ganglion cells (ipRGCs) respond directly to light and are responsible of the synchronization of the circadian rhythm with the photic stimulus and for the pupillary light reflex. To quantify the total population of rat-ipRGCs and to assess their spatial distribution we have developed an automated routine and used neighbour maps. Moreover, in all analysed retinas we have studied the general population of RGCs - identified by their Brn3a expression - and the population of ipRGCs - identified by melanopsin immunodetection - thus allowing the co-analysis of their topography. Our results show that the total mean number ± standard deviation of ipRGCs in the albino rat is 2047 ± 309. Their distribution in the retina seems to be complementary to that of Brn3a(+)RGCs, being denser in the periphery, especially in the superior retina where their highest densities are found in the temporal quadrant, above the visual streak. In addition, by tracing the retinas from both superior colliculi, we have also determined that 90.62% of the ipRGC project to these central targets.

Axotomy-induced retinal ganglion cell death in adult mice: quantitative and topographic time course analyses

The fate of retinal ganglion cells after optic nerve injury has been thoroughly described in rat, but not in mice, despite the fact that this species is amply used as a model to study different experimental paradigms that affect retinal ganglion cell population. Here we have analyzed, quantitatively and topographically, the course of mice retinal ganglion cells loss induced by intraorbital nerve transection. To do this, we have doubly identified retinal ganglion cells in all retinas by tracing them from their main retinorecipient area, the superior colliculi, and by their expression of BRN3A (product of Pou4f1 gene). In rat, this transcription factor is expressed by a majority of retinal ganglion cells; however in mice it is not known how many out of the whole population of these neurons express it. Thus, in this work we have assessed, as well, the total population of BRN3A positive retinal ganglion cells. These were automatically quantified in all whole-mounted retinas using a newly developed routine. In control retinas, traced-retinal ganglion cells were automatically quantified, using the previously reported method (Salinas-Navarro et al., 2009b). After optic nerve injury, though, traced-retinal ganglion cells had to be manually quantified by retinal sampling and their total population was afterwards inferred. In naïve whole-mounts, the mean (±standard deviation) total number of traced-retinal ganglion cells was 40,437(±3196) and of BRN3A positive ones was 34,697(±1821). Retinal ganglion cell loss was first significant for both markers 5 days post-axotomy and by day 21, the last time point analyzed, only 15% or 12% of traced or BRN3A positive retinal ganglion cells respectively, survived. Isodensity maps showed that, in control retinas, BRN3A and traced-retinal ganglion cells were distributed similarly, being densest in the dorsal retina along the naso-temporal axis. After axotomy the progressive loss of BRN3A positive retinal ganglion cells was diffuse and affected the entire retina. In conclusion, this is the first study assessing the values, in terms of total number and density, of the retinal ganglion cells surviving axotomy from 2 till 21 days post-lesion. Besides, we have demonstrated that BRN3A is expressed by 85.6% of the total retinal ganglion cell population, and because BRN3A positive retinal ganglion cells show the same spatial distribution and temporal course of degeneration than traced ones, BRN3A is a reliable marker to identify, quantify and assess, ex-vivo, retinal ganglion cell loss in this species.

Retinal ganglion cell population in adult albino and pigmented mice: a computerized analysis of the entire population and its spatial distribution

In adult Swiss albino and C57 pigmented mice, RGCs were identified with a retrogradely transported neuronal tracer applied to both optic nerves (ON) or superior colliculi (SCi). After histological processing, the retinas were prepared as whole-mounts, examined and photographed under a fluorescence microscope equipped with a motorized stage controlled by a commercial computer image analysis system: Image-Pro Plus((R)) (IPP). Retinas were imaged as a stack of 24-bit color images (140 frames per retina) using IPP with the Scope-Pro plug-in 5.0 and the images montaged to create a high-resolution composite of the retinal whole-mount when required. Single images were also processed by specific macros written in IPP that apply a sequence of filters and transformations in order to separate individual cells for automatic counting. Cell counts were later transferred to a spreadsheet for statistical analysis and used to generate a RGC density map for each retina.

RESULTS

The mean total numbers of RGCs labeled from the ON, in Swiss (49,493+/-3936; n=18) or C57 mice (42,658+/-1540; n=10) were slightly higher than the mean numbers of RGCs labeled from the SCi, in Swiss (48,733+/-3954; n=43) or C57 mice (41,192+/-2821; n=42), respectively. RGCs were distributed throughout the retina and density maps revealed a horizontal region in the superior retina near the optic disk with highest RGC densities. In conclusion, the population of mice RGCs may be counted automatically with a level of confidence comparable to manual counts. The distribution of RGCs adopts a form of regional specialization that resembles a horizontal visual streak.

A computerized analysis of the entire retinal ganglion cell population and its spatial distribution in adult rats

In adult albino (SD) and pigmented (PVG) rats the entire population of retinal ganglion cells (RGCs) was quantified and their spatial distribution analyzed using a computerized technique. RGCs were back-labelled from the optic nerves (ON) or the superior colliculi (SCi) with Fluorogold (FG). Numbers of RGCs labelled from the ON [SD: 82,818+/-3,949, n=27; PVG: 89,241+/-3,576, n=6) were comparable to those labelled from the SCi [SD: 81,486+/-4,340, n=37; PVG: 87,229+/-3,199; n=59]. Detailed methodology to provide cell density information at small scales demonstrated the presence of a horizontal region in the dorsal retina with highest densities, resembling a visual streak.

Selective innervation of retinorecipient brainstem nuclei by retinal ganglion cell axons regenerating through peripheral nerve grafts in adult rats

The pattern of axonal regeneration, specificity of reinnervation, and terminal arborization in the brainstem by axotomized retinal ganglion cell axons was studied in rats with peripheral nerve grafts linking the retina with ipsilateral regions of the brainstem, including dorsal and lateral aspects of the diencephalon and lateral aspect of the superior colliculus. Four to 13 months later, regenerated retinal projections were traced using intraocular injection of cholera toxin B subunit. In approximately one-third of the animals, regenerated retinal axons extended into the brainstem for distances of up to 6 mm. Although axons followed different patterns of ingrowth depending on their site of entry to the brainstem, within the pretectum, they innervated preferentially the nucleus of the optic tract and the olivary pretectal nucleus in which they formed two types of terminal arbors. Within the superior colliculus, axons extended laterally and formed a different terminal arbor type within the stratum griseum superficiale. In the remaining two-thirds of the animals, retinal fibers formed a neuroma-like structure at the site of entry into the brainstem, or a few fibers extended for very short distances within the neighboring neuropil. These experiments suggest that regenerated retinal axons are capable of a highly selective reinnervation pattern within adult denervated retinorecipient nuclei in which they form well defined terminal arbors that may persist for long periods of time. In addition, these studies provide the anatomical correlate for our previous functional study on the re-establishment of the pupillary light reflex in this experimental paradigm.

Extent and duration of recovered pupillary light reflex following retinal ganglion cell axon regeneration through peripheral nerve grafts directed to the pretectum in adult rats

The functional reinnervation of the olivary pretectal nucleus (OPN) was studied in adult rats with peripheral nerve (PN) grafts bridging the interrupted retinopretectal pathway. Functional recovery was assessed quantitatively using established pupillometry techniques. The effect of intravitreal tuftsin fragment 1-3 (tuftsin 1-3) injections during the grafting procedure was also studied. A total of 53 adult rats received autologous PN grafts connecting the ocular stump of the transected optic nerve to the ipsilateral OPN. The contralateral eye was enucleated to remove the input from that eye to the OPN. A pupillary light reflex was elicited from 35 of the 53 PN-grafted animals and in the best cases, a response was obtained which compared closely to that recorded from control animals. Tuftsin 1-3 was found to increase the rate of recovery of the response. The response amplitude of PN-grafted rats was generally found to diminish with repeated stimulus presentation and also appeared to deteriorate with age. This was in contrast to control animals' responses. However, a PLR could still be elicited in 3 of the 6 animals studied 15 months after PN-grafting. These findings indicate that a near-normal PLR function can be restored using a peripheral nerve graft, but there are a number of factors that are likely to compromise optimal outcome.

Myelopoiesis in the thymus of the sea bass, Dicentrarchus labrax L. (teleost)

BACKGROUND

In vertebrates the thymus is primarily regarded as a lymphoid organ whose importance lies in its capacity to produce a large number of lymphocytes that enter the circulation as T cells. In higher vertebrates the organ has also been regarded as a site for myelopoiesis, but this capacity has not been observed in fish. In this study we describe morphologically the presence of intrathymic developing myeloid cells in the sea bass.

METHODS

The thymus samples were morphologically studied by transmission electron microscopy.

RESULTS

We describe the coexistence of cells in different stages of erythropoiesis and granulopoiesis that appear to be developing in situ in some thymus lobes. Degenerated thymocytes and epithelial-reticular cells occur simultaneously in the same areas.

CONCLUSIONS

The coexistence of different cellular components of erythropoiesis and the heterophilic series of granulopoiesis with areas of necrosis suggests a relationship between both processes that is influenced by the microenvironment. Our observations also suggest that the presence of intrathymic developing myeloid cells may imply a nonimmunological role for the thymus.