Biomedical subjects

Thomas Pannicke

Publications and source records attributed to Thomas Pannicke.

At least 19 recordsLinked to original sources

PubMed2007

Müller cells as players in retinal degeneration and edema.

BACKGROUND: Under normal conditions, Müller cells support neuronal activity and the integrity of the blood-retinal barrier, whereas gliotic alterations of Müller cells under pathological conditions may contribute to retinal degeneration and edema formation. A major function of Müller cells is the fluid absorption from the retinal tissue, which is mediated by transcellular water transport coupled to currents through potassium channels. METHODS: Alterations of retinal Müller cells under pathological conditions were investigated by immunohistochemistry and recording their behavior under osmotic stress. RESULTS: In animal models of various retinopathies, e.g., retinal ischemia, ocular inflammation, retinal detachment, and diabetes, it was found that Müller cells decrease the expression of their major potassium channel (Kir4.1). This alteration is associated with an impairment of the rapid water transport across Müller cell membranes, as recognizable in the induction of cellular swelling under hypoosmolar conditions. Osmotic swelling of Müller cells is also induced by oxidative stress and by inflammatory mediators such as arachidonic acid and prostaglandins. CONCLUSIONS: The data suggest that a disturbed fluid transport through Müller cells is (in addition to vascular leakage) a pathogenic factor contributing to the development of retinal edema. Pharmacological re-activation of the retinal water clearance by Müller cells may represent an approach to the development of new edema-resolving drugs. Triamcinolone acetonide, which is clinically used to resolve edema, prevents osmotic swelling of Müller cells as it induces the release of endogenous adenosine and subsequent A1 receptor activation which results in the opening of ion channels. Apparently, triamcinolone resolves edema by both inhibition of vascular leakage and stimulation of retinal fluid clearance by Müller cells.

Animals↗

PubMed2006

Ischemia-reperfusion alters the immunolocalization of glial aquaporins in rat retina.

Glial cells control the retinal osmohomeostasis, in part via mediation of water fluxes through aquaporin (AQP) water channels. By using immunohistochemical staining, we investigated whether ischemia-reperfusion of the rat retina causes alterations in the distribution of AQP1 and AQP4 proteins. Transient ischemia was induced in retinas of Long-Evans rats by elevation of the intraocular pressure for 60 min. In control retinas, immunoreactive AQP1 was expressed in the outer retina and by distinct amacrine cells, and AQP4 was expressed by glial cells (Müller cells and astrocytes) predominantly in the inner retina. After ischemia, retinal glial cells in the nerve fiber/ganglion cell layers strongly expressed AQP1. The perivascular staining around the superficial vessels altered from AQP4 in control retinas to AQP1 in postischemic retinas. The data suggest that the glial cell-mediated water transport in the retina is altered after ischemia especially at the superficial vessel plexus.

Animals↗

PubMed2006

Müller cells in the healthy and diseased retina.

Müller glial cells span the entire thickness of the tissue, and ensheath all retinal neurons, in vertebrate retinae of all species. This morphological relationship is reflected by a multitude of functional interactions between neurons and Müller cells, including a 'metabolic symbiosis' and the processing of visual information. Müller cells are also responsible for the maintenance of the homeostasis of the retinal extracellular milieu (ions, water, neurotransmitter molecules, and pH). In vascularized retinae, Müller cells may also be involved in the control of angiogenesis, and the regulation of retinal blood flow. Virtually every disease of the retina is associated with a reactive Müller cell gliosis which, on the one hand, supports the survival of retinal neurons but, on the other hand, may accelerate the progress of neuronal degeneration: Müller cells protect neurons via a release of neurotrophic factors, the uptake and degradation of the excitotoxin, glutamate, and the secretion of the antioxidant, glutathione. However, gliotic Müller cells display a dysregulation of various neuron-supportive functions. This contributes to a disturbance of retinal glutamate metabolism and ion homeostasis, and causes the development of retinal edema and neuronal cell death. Moreover, there are diseases evoking a primary Müller cell insufficiency, such as hepatic retinopathy and certain forms of glaucoma. Any impairment of supportive functions of Müller cells, primary or secondary, must cause and/or aggravate a dysfunction and loss of neurons, by increasing the susceptibility of neurons to stressful stimuli in the diseased retina. On the contrary, Müller cells may be used in the future for novel therapeutic strategies to protect neurons against apoptosis (somatic gene therapy), or to differentiate retinal neurons from Müller/stem cells. Meanwhile, a proper understanding of the gliotic responses of Müller cells in the diseased retina, and of their protective vs. detrimental effects, is essential for the development of efficient therapeutic strategies that use and stimulate the neuron-supportive/protective-and prevent the destructive-mechanisms of gliosis.

Animals↗

PubMed2006

The developmental expression of K+ channels in retinal glial cells is associated with a decrease of osmotic cell swelling.

A major function of glial cells is the control of osmotic and ionic homeostasis, mediated by K+ and water movements predominantly through inwardly rectifying K+ (Kir) and aquaporin water channels. It has been suggested that K+ currents through Kir channels are implicated in the regulation of glial cell volume. Here, we investigated whether the developmental increase in Kir channel expression in Müller glial cells of the rat retina is associated with an alteration of cell volume regulation under anisoosmotic conditions. Around the time of eye opening at postnatal day (P) 15, developing retinal glial cells fully alter the profile of their membrane conductances, from a current pattern with prominent fast transient K+ and Na+ currents to a pattern of noninactivating currents through Kir and delayed rectifier K+ channels. Concomitantly, aquaporins-1 and -4 are expressed in the developing retina. This is accompanied by a conspicuous alteration of the swelling characteristics of cells; somata of immature glial cells in early postnatal retinas (P5-P15) swell under hypotonic stress but no swelling is inducible in mature cells at P18 and thereafter. However, glial cells at all developmental stages swell when their Kir channels are blocked by Ba2+. The postnatal maturation of Kir channel currents and volume regulation in retinal glial cells is delayed by visual deprivation. The data suggest that Kir channels are crucially involved in osmotic volume homeostasis of mature glial cells, and that the absence of Kir channels in immature cells is a major cause of their insufficient volume regulation.

Animals↗

PubMed2006

Glial cell reactivity in a porcine model of retinal detachment.

PURPOSE: Detachment of the neural retina from the pigment epithelium causes, in addition to photoreceptor deconstruction and neuronal cell remodeling, an activation of glial cells. It has been suggested that gliosis contributes to the impaired recovery of vision after reattachment surgery that may involve both formerly detached and nondetached retinal areas. Müller and microglial cell reactivity was monitored in a porcine model of rhegmatogenous retinal detachment, to determine whether gliosis is present in detached and nondetached retinal areas. METHODS: Local detachment was created in the eyes of adult pigs by subretinal application of hyaluronate. Retinal slices were immunostained against glial intermediate filaments and K+ and water channel proteins (aquaporin-4, Kir4.1, Kir2.1), and P2Y receptor proteins. In retinal wholemounts, adenosine 5'-triphosphate (ATP)-induced intracellular Ca2+ responses of Müller cells were recorded, and microglial and immune cells were labeled with Griffonia simplicifolia agglutinin isolectin I-B4. K+ currents were recorded from isolated Müller cells. RESULTS: At 3 and 7 days after surgery, Müller cells in detached retinas showed a pronounced gliosis, as revealed by the increased expression of the intermediate filaments glial fibrillary acidic protein and vimentin, by the decrease of Kir4.1 immunoreactivity and of the whole-cell K+ currents, and by the increased incidence of cells that showed Ca2+ responses on stimulation of purinergic (P)2 receptors by ATP. By contrast, the immunohistochemical expression of Kir2.1 and aquaporin-4 were not altered after detachment. The increase in the expression of intermediate filaments, the decrease of the whole-cell K+ currents and of the Kir4.1 immunolabeling, and the increase in the Ca2+ responsiveness of Müller cells were also observed in attached retinal areas surrounding the focal detachment. The density of microglial-immune cells at the inner surface of the retinas increased in both detached and nondetached retinal areas. The immunoreactivities for P2Y1 and P2Y2 receptor proteins apparently increased only in detached areas. CONCLUSIONS: Reactive responses of Müller and microglial cells are not restricted to detached retinal areas but are also observed in nondetached regions of the porcine retina. The gliosis in the nondetached retina may reflect, or may contribute to, neuronal degeneration that may explain the impaired recovery of vision observed in human subjects after retinal reattachment surgery.

Animals↗

PubMed2006

Diabetes alters osmotic swelling characteristics and membrane conductance of glial cells in rat retina.

The development of edema in the diabetic retina may be caused by vascular leakage and glial cell swelling. To determine whether diabetic retinopathy alters the swelling characteristics of retinal glial cells and changes the properties of the glial membrane K+ conductance, isolated retinas and glial cells of rats were investigated at 4 and 6 months of chemical diabetes. After 6 months of hyperglycemia, application of a hypotonic solution to retinal slices induced swelling of glial cell bodies, a response not observed in control retinas. The osmotic glial cell swelling was blocked by inhibitors of phospholipase A2 or cyclooxygenase and by a thiol-reducing agent. Glial cells from diabetic retinas displayed a decrease of K+ currents that was associated with an altered subcellular distribution of the K+ conductance and a loss of perivascular Kir4.1 protein. The observation that swelling of cells in control retinas was inducible with K+ channel-blocking Ba2+ ions suggests a relationship between decreased K+ inward currents and osmotic cell swelling in diabetic retinas. The data show that glial cells in diabetic retinas are more sensitive to osmotic stress, which is associated with a decrease of K+ currents, than cells in control retinas. It is suggested that these alterations may be implicated in the development of diabetic retinal edema.

Animals↗

PubMed2006

Changes in membrane conductance play a pathogenic role in osmotic glial cell swelling in detached retinas.

Detachment of the neural retina from the pigment epithelium may be associated with tissue edema; however, the mechanisms of fluid accumulation are not understood. Because retinal detachment is usually not accompanied by vascular leakage, we investigated whether the osmotic swelling characteristics of retinal glial (Müller) cells are changed after experimental detachment of the porcine retina. Osmotic stress, induced by application of a hypotonic bath solution to retinal slices, caused swelling of Müller cell bodies in 7-day-detached retinas, but no swelling was inducible in slices of control retinas. Müller cell somata in slices of retinal areas that surround local detachment in situ also showed osmotic swelling, albeit at a smaller amplitude. The amplitude of osmotic Müller cell swelling correlated with the decrease in the K+ conductance, suggesting a causal relationship between both gliotic alterations. Further factors implicated in Müller cell swelling were inflammatory mediators and oxidative stress. We propose that a dysregulation of the ion and water transport through Müller cells may impair the fluid absorption from the retinal tissue, resulting in chronic fluid accumulation after detachment. This knowledge may lead to a better understanding of the mechanisms involved in retinal degeneration after detachment.

Animals↗

PubMed2005

Differential regulation of Kir4.1 and Kir2.1 expression in the ischemic rat retina.

Ischemia-reperfusion of the rat retina causes gliosis of Müller cells that is associated with a decrease of their K+ conductance. By using quantitative PCR and immunohistochemical staining of retinal slices, we investigated the effect of transient ischemia-reperfusion on retinal expression of two inward-rectifying K+ (Kir) channels, Kir4.1 and Kir2.1. In control retinas, Müller cells prominently expressed both Kir4.1 and Kir2.1 proteins. At 7 days after reperfusion, the expression of Kir4.1 protein was strongly downregulated, while the Kir2.1 protein expression remained unaltered. The expression of Kir4.1 mRNA was reduced by 55% after ischemia while the expression of Kir2.1 mRNA was not altered. The data suggest that the glial expression of distinct Kir channels is differentially regulated after retinal ischemia, with deletarious consequences for K+ ion and water homeostasis.

Animals↗

PubMed2005

Expression of aquaporin-1 immunoreactivity by photoreceptor cells in the mouse retina.

Aquaporin water channels play a crucial role in the maintenance of ionic and osmotic homeostasis in the neural tissue. In the sensory retina, aquaporin-4 is expressed by Müller glial cells, predominantly in the inner retina, while aquaporin-1 is expressed mainly in the outer retina. However, it is unknown whether aquaporin-1 expression occurs in Müller cells or photoreceptor cells. By using immunohistochemical staining of retinal slices from rds mice, we show that the immunoreactivity for aquaporin-1 disappears along with the photoreceptor cell degeneration. In suspensions of dissociated retinal cells from control mice, photoreceptor cells expressed aquaporin-1 immunoreactivity while Müller cells were largely devoid of staining. The data suggest that photoreceptor cells, but not Müller cells, express aquaporin-1 in the murine retina.

Animals↗

PubMed2005

Atypical gliosis in Müller cells of the slowly degenerating rds mutant mouse retina.

Retinal Müller glial cells are known to undergo reactive changes (gliosis) in various retinal diseases. In virtually all cases studied, an upregulation of glial fibrillary acidic protein (GFAP) and a hypertrophy can be observed. Physiological alterations, such as a strong downregulation of inwardly rectifying K+ (Kir) currents, were found after retinal detachment (man, rabbit) and after ischemia/reperfusion (rat) but not in more slowly progressing retinal degenerations (Borna Disease Virus-infected rats, RCS rats). This led us to hypothesize that Müller cells respond with 'typical' reactive gliosis only to rapid but not to slow retinal degeneration. To test this hypothesis, we studied Müller cells from rds mutant mice (PrphRd2), which show a retinal degeneration of early onset and slow progression, resulting in a complete loss of photoreceptors after 9-12 months. In Müller cells of rds mice, we found immunoreactivity for GFAP, a marker of gliosis in Müller cells, from postnatal day 21 on, accompanied by a moderately increased membrane capacitance (taken as an indicator of hypertrophy), whereas no change in the expression of the Kir4.1 protein occurred in adult rds mice. We failed to observe significant changes in the membrane resistance and the membrane potential of cells from rds mice from first week after birth until 1 year of age. Current densities were decreased in cells from 3- and 5-week old rds mice. Furthermore, as in control cells from wildtype animals, these cells displayed dominant Kir currents, voltage-dependent Na+ currents, and glutamate uptake currents. These data support the idea that in mice as well as previously shown in rats, slow retinal degeneration induces an atypical gliosis of Müller cells.

Animals↗

PubMed2005

The glucocorticoid triamcinolone acetonide inhibits osmotic swelling of retinal glial cells via stimulation of endogenous adenosine signaling.

The glucocorticoid triamcinolone acetonide is clinically used for the treatment of macular edema. However, the edema-resolving mechanisms of triamcinolone are incompletely understood. Since cell swelling is a central cause of cytotoxic edema in the brain and retina, we determined the effects of triamcinolone acetonide on the swelling of retinal ganglion and Müller glial cells in acutely isolated retinas from rats and guinea pigs in situ. Triamcinolone acetonide (100 microM) had no effect on the swelling of ganglion cells that was evoked in isolated whole mounts of the guinea pig retina by acute application of glutamate (1 mM) or high K+ (50 mM). However, triamcinolone reversed the osmotic swelling of Müller glial cells in retinas of the rat that was observed under various experimental conditions: in retinas isolated at 3 days after transient retinal ischemia, in retinas of eyes with lipopolysaccharide-induced ocular inflammation, and in control retinas in the presence of Ba2+ (1 mM), H2O2 (200 microM), arachidonic acid (10 microM), or prostaglandin E2 (30 nM). The inhibiting effect of triamcinolone on osmotic glial cell swelling was mediated by stimulation of transporter-mediated release of endogenous adenosine and subsequent A1 receptor activation, resulting in an elevation of the intracellular cAMP level and activation of the protein kinase A, and, finally, in an opening of extrusion pathways for K+ and Cl- ions. The inhibitory effect on the cytotoxic swelling of glial cells may contribute to the fast edema-resolving effect of vitreal triamcinolone observed in human patients.

Adenosine↗

PubMed2005

Glial cell-mediated spread of retinal degeneration during detachment: a hypothesis based upon studies in rabbits.

In human subjects with peripheral retinal detachments, visual deficits are not restricted to the detached retina but are also present in the non-detached tissue. Based upon studies on a rabbit model of rhegmatogenous retinal detachment, we propose a glial cell-mediated mechanism of spread of retinal degeneration into non-detached retinal areas which may also have importance for the understanding of alterations in the human retina. Both detached and attached portions of the rabbit retina display photoreceptor cell degeneration and cystic degeneration of the innermost layers. An inverse mode of photoreceptor cell degeneration in the attached tissue suggests a disturbed support of the photoreceptor cells by Müller cells which show various indications of gliosis (increased expression of intermediate filaments, cell hypertrophy, decreased plasma membrane K(+) conductance, increased Ca(2+) responsiveness to purinergic stimulation) in both detached and attached tissues. We propose that gliotic alterations of Müller cells contribute to the degeneration of the attached retina, via disturbance of glial homeostasis mechanisms. A down-regulation of the K(+) conductance of Müller cells may prevent effective retinal K(+) and water clearance, and may favor photoreceptor cell degeneration and edema development.

Adenosine Triphosphate↗

PubMed2005

Altered membrane physiology in Müller glial cells after transient ischemia of the rat retina.

Inwardly rectifying K+ (Kir) channels have been implicated in the mediation of retinal K+ homeostasis by Muller glial cells. To assess possible involvement of altered glial K+ channel expression in ischemia-reperfusion injury, transient retinal ischemia was induced in rat eyes. Acutely isolated Muller cells from postischemic retinae displayed a fast downregulation of their Kir currents, which began within 1 day and reached a maximum at 3 days of reperfusion, with a peak decrease to 20% as compared with control. This strong decrease of Kir currents was accompanied by an increase of the incidence of cells which displayed depolarization-evoked fast transient (A-type) K+ currents. While no cell from untreated control rats expressed A-type K+ currents, all cells investigated from 3- and 7-day postischemic retinae displayed such currents. An increased incidence of cells displaying fast transient Na+ currents was observed at 7 days after ischemia. These results suggest a role of altered glial Kir channel expression in postischemic neuronal degeneration via disturbance of retinal K+ siphoning.

Animals↗

PubMed2005

Glutamate transport by retinal Muller cells in glutamate/aspartate transporter-knockout mice.

Glutamate transporters are involved in maintaining extracellular glutamate at a low level to ensure a high signal-to-noise ratio for glutamatergic neurotransmission and to protect neurons from excitotoxic damage. The mammalian retina is known to express the excitatory amino acid transporters, EAAT1-5; however, their specific role in glutamate homeostasis is poorly understood. To examine the role of the glial glutamate/aspartate transporter (GLAST) in the retina, we have studied glutamate transport by Muller cells in GLAST-/- mice, using biochemical, electrophysiological, and immunocytochemical techniques. Glutamate uptake assays indicated that the Km value for glutamate uptake was similar in wild-type and GLAST-/- mouse retinas, but the Vmax was approximately 50% lower in the mutant. In Na+-free medium, the Vmax was further reduced by 40%. In patch-clamp recordings of dissociated Muller cells from GLAST-/- mice, application of 0.1 mM glutamate evoked no current showing that the cells lacked functional electrogenic glutamate transporters. The result also indicated that there was no compensatory upregulation of EAATs in Muller cells. [3H]D-Aspartate uptake autoradiography, however, showed that Na+-dependent, high-affinity transporters account for most of the glutamate uptake by Muller cells, and that Na+-independent glutamate transport is negligible. Additional experiments showed that the residual glutamate uptake in Muller cells in the GLAST-/- mouse retina is not due to known glutamate transporters-cystine-glutamate exchanger, ASCT-1, AGT-1, or other heteroexchangers. The present study shows that while several known glutamate transporters are expressed by mammalian Muller cells, new Na+-dependent, high-affinity glutamate transporters remain to be identified.

Amino Acid Transport System ASC↗

PubMed2005

Ocular inflammation alters swelling and membrane characteristics of rat Müller glial cells.

Ocular inflammation is a common cause of retinal edema that may involve swelling of Müller glial cells. In order to investigate whether endotoxin-induced ocular inflammation in rats alters the swelling and membrane characteristics of Müller cells, lipopolysaccharide (LPS; 0.5%) was intravitreally injected. At 3 and 7 days after treatment, hypotonic challenge induced swelling of Müller cell somata that was not observed in non-treated control eyes. Müller cells of LPS-treated eyes displayed a downregulation of inward K(+) currents and upregulation of A-type K(+) currents that was associated with a decreased expression of Kir4.1 protein in retinal slices. The data suggest that ocular inflammation induces alterations of both the swelling characteristics and the K(+) channel expression of Müller cells.

Analysis of Variance↗

PubMed2005

Physiological properties of retinal Muller glial cells from the cynomolgus monkey, Macaca fascicularis--a comparison to human Muller cells.

Retinae from rabbits and laboratory rodents are often used as 'models' of the human retina, although there are anatomical differences. To test whether monkey eyes provide a better model, a physiological study of Muller glial cells was performed comparing isolated cells and retinal wholemounts from the cynomolgus monkey, Macaca fascicularis and from man. The membrane conductance of Muller cells from both species was dominated by inward and outward K(+) currents. Cells displayed glutamate uptake currents and responded to nucleotides by intracellular Ca(2+) increases. However, there were also species differences, such as a lack of GABA(A) receptors and of Ca(2+)-dependent K(+) currents in monkey cells. Thus, the use of Muller cells from cynomolgus monkeys may be advantageous for investigating a few specific properties; in general, monkey cells are no more similar to human cells than those from standard laboratory animals.

Adult↗

PubMed2005

Triamcinolone does not alter glial cell activation in the experimentally detached rabbit retina.

AIMS: Retinal detachment induces neural and photoreceptor cell degeneration and fast activation of micro- (immune) and macroglial cells. Hypoxia caused by increased distance between the choriocapillaris and the neural retina, and retinal oedema during detachment, are factors causing gliotic responses and cell degeneration. Triamcinolone may inhibit some cellular responses that accompany hypoxia. Therefore, we investigated whether triamcinolone acetonide may be effective to reduce the gliotic alterations in the detached retina. METHODS: Local retinal detachment in rabbit eyes was created by subretinal injection of sodium hyaluronate, and triamcinolone acetonide (8 mg) was applied intravitreally. Wholecell patch-clamp records from Muller cells and Ca2+ imaging from retinal wholemounts were carried out. Microglial/immune cells in the nerve-fiber layer of retinal wholemounts were labeled with Griffonia simplicifolia agglutinin (GSA) isolectin. Additionally, two morphological parameters which characterize microglial activation/immune cell infiltration were estimated: the cross-sectional area of the somata of the cells in the nerve-fiber layer and the number of cell processes which evolve from the soma. RESULTS: Three days after detachment, gliotic alterations were apparent in Muller cells isolated from both detached and nondetached retinal areas, as indicated by the cellular hypertrophy, by the downregulation of the plasma membrane K+ conductance, and by the upregulation of intracellular Ca2+ responsiveness to stimulation of purinergic P2Y receptors. Intravitreal triamcinolone did not alter these gliotic alterations of Muller cells. Furthermore, triamcinolone could not inhibit the immune cell activation present in detached and attached retinal areas. However, intravitreal triamcinolone led to a strong decrease in the process number of GSA lectin-positive cells from detached retinas. CONCLUSIONS: The results suggest that triamcinolone is ineffective to inhibit gliotic responses in the detached retina. However, the immune cell activation after detachment was partially influenced by triamcinolone.

Animals↗

PubMed2005

Neuronal versus glial cell swelling in the ischaemic retina.

Under normal conditions, the pigment epithelium dehydrates the outer retina while Müller glial cells mediate the rapid water transport within the inner retina. Gliotic alterations of Müller cells may be implicated in the development of oedema in the post-ischaemic retina. Here, we suggest a mechanism of Müller cell-supported neuronal cell swelling and apoptosis in the ischaemic retina. During ischaemia, over-excitation of ionotropic glutamate receptors leads to neuronal cell depolarization that causes excess Ca(2+) influx into the cells, and to activation of the apoptosis machinery. The ion fluxes into the retinal neurons are associated with water movements that are mediated by aquaporin-4 water channels expressed by Müller cells and result in neuronal cell swelling. After reperfusion, the glial cells may swell due to the down-regulation of their K(+) conductance, which results in intracellular K(+) overload and water movements from the blood and vitreous into the cells. An inhibition of the glial cell-mediated water movements during ischaemic episodes should reduce the ion shifts at the neuronal synapses, resulting in decreased neuronal cell swelling and apoptosis. An inhibition of the water movements in the post-ischaemic phase may prevent cytotoxic Müller cell swelling but may impair the fluid clearance from retinal tissue in the presence of vasogenic oedema. Thus, pharmacological modification of the ion and fluid clearance functions of Müller cells may become a novel way to resolve both cytotoxic and vasogenic oedema in the retina.

Animals↗