Home   User Center   Featured   Recent   Search   Submission   Manuscripts  

Journal of Nature and Science (JNSCI), Vol.1, No.5, e103, 2015
Abstract  Full Text (PDF)  Cite this article

Neuroscience

 

Subtype-dependent Morphological and Functional Degeneration of Retinal Ganglion Cells in Mouse Models of Experimental Glaucoma

 

Zhen Puyang1,2, Hui Chen1, Xiaorong Liu1, 3,*

 

1Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA. 2School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. 3Department of Neurobiology, Weinberg College of Arts and Sciences, Northwestern University, Evanston, Illinois 60208, USA


In this short review, Puyang and her colleagues compared the results from three laboratories on the dendritic and functional degeneration of retinal ganglion cells (RGCs) in mouse models of experimental glaucoma [1-4].  Acute or chronic ocular hypertension was induced in mice, and different techniques were applied to identify RGC types. The dendritic alternations of RGCs were examined following the induction of ocular hypertension, and their light response properties were characterized by the multi-electrode array (MEA) recording. These studies support the notion that the morphological and functional degeneration of RGCs are subtype-dependent in experimental glaucoma. Journal of Nature and Science, 1(5):e103, 2015

 

Retinal Ganglion Cells (RGCs) | Experimental Glaucoma | Dendritic Degeneration | Multi-Electrode Array (MEA)

 

Many studies suggested that subtle changes in dendritic structure and synaptic functions of RGCs precede cell death in mice with experimental glaucoma [5, 6]. Therefore, characterization of morphological and functional degeneration of RGCs at early stages of glaucoma may open a time window for treatment to prevent subsequent vision loss. There are more than 20 distinct types of RGCs in mouse [7-11], which makes it challenging to profile how each RGC type degenerates with glaucoma progression. Combined mouse genetics, molecular biology, and physiology, studies began to reveal the effects of glaucomatous insult on different RGC types. In this review, we compared the results from three laboratories on the subtype-dependent degeneration of RGCs in mice with experimental glaucoma [1-4].

Because elevated intraocular pressure (IOP) is an important risk factor for the development of glaucoma, ocular hypertension is often induced in mice to mimic human high-tension glaucoma (Table 1). Injection of polystyrene microbeads into the anterior chamber, which occludes the aqueous outflow, induces acute IOP elevation [3, 12]. Repeated injections can be applied in order to maintain long-term IOP elevation [2, 12]. By comparison, laser illumination was applied to the corneal limbus to photocoagulate the aqueous outflow, which in turn induced IOP elevation for more than 2 months [1, 4, 13]. We further combined microbead injection and laser illumination into one procedure to achieve IOP elevation up to 5 months [4].

Different methods/techniques were applied to characterize RGC types. El-Danaf and his colleagues used two transgenic mouse lines which had OFF-α RGCs and direction-selective RGCs (DSGCs) labeled, respectively [3]. DSGCs filled with Alexa Fluor 555 hydrazide were separated into two groups: ON- and ON-OFF DSGCs [3]. Thy-1-YFP mice were also used which had a small number of RGCs labeled [1, 2, 9, 14]. Based on the signature laminar pattern of alpha-like RGCs,  they were classified into ON-sustained (A-Type ON-S), OFF-sustained (A-Type OFF-S), and OFF-transient (A-Type OFF-T) subtypes [2, 15]. We classified RGCs into ON, OFF, and ON-OFF types also based on the lamination pattern of dendrites in the inner plexiform layer (IPL) [1]. In addition, immunostaining with antibodies against melanopsin and SMI-32 were performed to label specific RGC types [1, 3, 9, 16].

As early as one week post IOP elevation, one of the major morphological changes is the dendritic alternation in the OFF sublaminar of the IPL [3]. At 2-4 weeks post IOP elevation, Della Santina and his colleagues showed that OFF-transient RGCs exhibited decreased dendritic coverage, dendritic length, and number of dendrites [2]. At 6-8 weeks post IOP elevation, we found that the dendritic coverage of mono-laminated ON but not bi-laminated ON-OFF cells decreased [1]. We further showed that the dendritic branching of a subtype of ON cells, the SMI-32-positive ON cells, was significantly reduced [1]. All these studies suggested that deterioration of dendritic morphology was detected at the very early stage of glaucoma and that the dendritic trees of RGCs continued to degenerate in a subtype-dependent manner.

Given that the dendritic structure of an RGC determines its function in visual information processing, the light response properties of an RGC may be altered correspondingly. Studies from two laboratories using the MEA recording demonstrated that the functional degeneration of RGCs is also subtype-dependent (Table 2) [2, 4]. Wong laboratory classified RGCs into ON and OFF cells based on their responses to a square-wave stimulus, then subgrouped them to sustained or transient types [2]. Spike-triggered average (STA) analysis was applied to characterize a neuron's receptive field (RF) properties [2]. By contrast, we applied the non-centered spike-triggered covariance (STC-NC) analysis to classify RGCs into ON, OFF, and ON-OFF three types [4, 17]. In both studies, the activity strength of RGCs were investigated [1, 2, 4]. Wong laboratory reported that, at 4 weeks post IOP elevation, the spontaneous activities and maximal spike rate of the light responses decreased for ON-sustained, OFF-sustained and OFF -transient RGCs, but not for ON-transient cells [2]. Our data showed that the average firing rates of all visually-responsive RGCs decreased after five weeks of IOP elevation [4]. Wong laboratory demonstrated that the RF sizes of OFF-transient RGCs significantly decreased [2], similar to our findings [4]. In addition, we showed that the RF sizes of ON RGCs, but not ON-OFF RGCs, were reduced [4]. Interestingly, the large ON and OFF RGCs were very sensitive to the hypertensive insult [4], consistent with the morphological studies in monkey and cat with experimental glaucoma [18, 19]. Together our studies as well as studies from other groups support the notion that the dendritic and functional degeneration of RGCs are subtype-dependent in experimental glaucoma.

Many important questions remain unanswered. For example, the dendritic degeneration of an RGC subtype does not always correlate with its functional changes as listed in Tables 1 and 2. Moreover, how do different RGC subtypes respond differently to the hypertensive insult?  Some studies suggested that the different susceptibility to pressure in RGCs could be due to the differential expression of transient receptor potential vanilloid (TRPV) channels [20-22]. The vasculature structure may also contribute to the dendritic degeneration of RGCs. For example, the OFF sublamina, unlike the ON sublamina of the IPL, is highly vascularized with capillaries, which makes the OFF sublamina more vulnerable than the ON sublamina at the early stage of IOP elevation [3]. Early signs of RGC damage have also been detected at the axon terminals [23-25]. Selective damage of axons may also contribute to the subtype-dependent RGC loss [4, 22-24]. Finally, during development, RGCs mature also in a subtype-dependent manner [9, 26, 27]. Misregulation of RGC structure and synaptic function during development leads to devastating vision losses such as in the childhood glaucoma. A new mouse model in which IOP was elevated dramatically during the first month after birth provides an opportunity to examine how development and function of RGCs are misregulated in the diseased condition [28]. More studies are needed to better understand the subtype-dependent RGC degeneration and its underlying mechanisms, which will add important insights on how to protect RGCs and vision in glaucoma.

 


Table 1. Morphological Degeneration of RGCs in Mouse Models of Experimental Glaucoma.

References

Mouse model

IOP

elevation

Duration of IOP elevation

Dendritic field size

Dendritic branching pattern

Parameters measured

Changes

El-Danaf and Huberman, 2014

Microbead injection

mild, acute

1 week

α OFF-transient ↓

ON, ON-OFF DSGC and M1 ipRGC ↔

dendritic complexity, number and total length of dendrites

OFF sublaminar ↓

ON sublaminar ↔

Della Santina, et al., 2013

Microbead

injections

modest, chronic

2 – 4 weeks

OFF-transient ↓

ON and OFF-sustained ↔

ON transient: not analyzed

dendritic complexity, number and total length of dendrites

OFF-transient ↓

ON and OFF-sustained ↔

Feng, et al., 2013

Laser illumination

modest, chronic

6 – 8 weeks

ON↓

ON-OFF↔

OFF: not analyzed.

total length of dendrites

SMI-32-positive ON ↓

Note 1. DSGC: direction-selective ganglion cell; ipRGC: intrinsically photosensitive retinal ganglion cells.

Note 2. ↓ significant decrease; ↔ No significant change (same for Table 2).

 

Table 2. Functional Degeneration of RGCs in Experimental Glaucoma.

References

Duration of IOP elevation

Subtypes

Spontaneous Activity

Spike Rate of the Light Responses

Receptive Field (RF) Size

Della Santina, et al., 2013

2 – 4 weeks

ON-sustained

ON-transient

OFF-sustained

OFF-transient

Chen, et al., 2015

5 – 6 weeks

ON

 

OFF

ON-OFF

 

Acknowledgments

This work was supported by the National Institutes of Health (NIH) grant R01EY019034 (to X.L.), the Dr. Douglas H. Johnson Award for Glaucoma Research from BrightFocus Foundation (to X.L.), Northwestern Memorial Foundation/Brinson Foundation (to X.L.), and the unrestricted RPB grant to the Department of Ophthalmology, Northwestern University.


 


This manuscript mainly reviewed the following 4 papers:

1.    Feng L, Zhao Y, Yoshida M, Chen H, Yang JF, Kim TS, Cang J, Troy JB, Liu X. Sustained ocular hypertension induces dendritic degeneration of mouse retinal ganglion cells that depends on cell type and location. Invest Ophthalmol Vis Sci, 2013. 54(2): 1106-1117.

2.    Della Santina L, Inman DM, Lupien CB, Horner PJ, Wong RO. Differential progression of structural and functional alterations in distinct retinal ganglion cell types in a mouse model of glaucoma. J Neurosci, 2013. 33(44): 17444-17457.

3.    El-Danaf RN, Huberman AD. Characteristic patterns of dendritic remodeling in early-stage glaucoma: evidence from genetically identified retinal ganglion cell types. J Neurosci, 2015. 35(6): 2329-2343.

4.    Chen H, Zhao Y, Liu M, Feng L, Puyang Z, Yi J, Liang P, Zhang HF, Cang J, Troy JB, Liu X. Progressive degeneration of retinal and superior collicular functions in mice with sustained ocular hypertension. Invest Ophthalmol Vis Sci, 2015. 56(3): 1971-1984.

 

Other References:

5.  Morgan JE. Retina ganglion cell degeneration in glaucoma: an opportunity missed? A review. Clin Experiment Ophthalmol, 2012. 40(4): 364-368.

6.  Calkins DJ. Critical pathogenic events underlying progression of neurodegeneration in glaucoma. Prog Retin Eye Res, 2012. 31(6): 702-719.

7.  Völgyi B, Chheda S, Bloomfield SA. Tracer coupling patterns of the ganglion cell subtypes in the mouse retina. J Comp Neurol, 2009. 512(5): 664-687.

8.  Sun W, Li N, He S. Largescale morphological survey of mouse retinal ganglion cells. J Comp Neurol, 2002. 451(2): 115-126.

9.  Liu X, Grishanin RN, Tolwani RJ, Rentería RC, Xu B, Reichardt LF, Copenhagen DR. Brain-derived neurotrophic factor and TrkB modulate visual experience-dependent refinement of neuronal pathways in retina. J Neurosci, 2007. 27(27): 7256-7267.

10.  Badea TC, Nathans J. Quantitative analysis of neuronal morphologies in the mouse retina visualized by using a genetically directed reporter. J Comp Neurol, 2004. 480(4): 331-351.

11.  Sanes JR, Masland RH. The types of retinal ganglion cells: current status and implications for neuronal classification. Annu Rev Neurosci, 2015. dio:10.1146/annurev-neuro-071714-034120.

12.  Sappington RM, Carlson BJ, Crish SD, Calkins DJ. The microbead occlusion model: a paradigm for induced ocular hypertension in rats and mice. Invest Ophthalmol Vis Sci, 2010. 51(1): 207-216.

13.  Feng L, Chen H, Suyeoka G, Liu X. A laser-induced mouse model of chronic ocular hypertension to characterize visual defects. J Vis Exp, 2013. 78: e50440. doi:10.3791/50440.

14.  Feng G, Mellor RH, Bernstein M, Keller-Peck C, Nguyen QT, Wallace M, Nerbonne JM, Lichtman JW, Sanes JR. Imaging neuronal subsets in transgenic mice expressing multiple spectral variants of GFP. Neuron, 2000. 28(1): 41-51.

15.  Margolis DJ, Detwiler PB. Different mechanisms generate maintained activity in ON and OFF retinal ganglion cells. J Neurosci, 2007. 27(22): 5994-6005.

16.  Coombs J, van der List D, Wang GY, Chalupa LM. Morphological properties of mouse retinal ganglion cells. Neuroscience, 2006. 140(1): 123-136.

17.  Cantrell DR, Cang J, Troy JB, Liu X. Non-centered spike-triggered covariance analysis reveals neurotrophin-3 as a developmental regulator of receptive field properties of ON-OFF retinal ganglion cells. PLoS Comput Biol, 2010. 6(10): e1000967. doi: 10.1371/journal.pcbi.1000967.

18.  Glovinsky Y, Quigley HA, Dunkelberger GR. Retinal ganglion cell loss is size dependent in experimental glaucoma. Invest Ophthalmol Vis Sci, 1991. 32(3): 484-491.

19.  Troy JB, Shou T. The receptive fields of cat retinal ganglion cells in physiological and pathological states: where we are after half a century of research. Prog Retin Eye Res, 2002. 21(3): 263-302.

20.  Sappington RM, Sidorova T, Long DJ, Calkins DJ. TRPV1: contribution to retinal ganglion cell apoptosis and increased intracellular Ca2+ with exposure to hydrostatic pressure. Invest Ophthalmol Vis Sci, 2009. 50(2): 717-728.

21.  Ward NJ, Ho KW, Lambert WS, Weitlauf C, Calkins DJ. Absence of transient receptor potential vanilloid-1 accelerates stress-induced axonopathy in the optic projection. J Neurosci, 2014. 34(9): 3161-3170.

22.  Weitlauf C, Ward NJ, Lambert WS, Sidorova TN, Ho KW, Sappington RM, Calkins DJ. Short-term increases in transient receptor potential vanilloid-1 mediate stress-induced enhancement of neuronal excitation. J Neurosci, 2014. 34(46): 15369-15381.

23.  Baltan S, Inman DM, Danilov CA, Morrison RS, Calkins DJ, Horner PJ. Metabolic vulnerability disposes retinal ganglion cell axons to dysfunction in a model of glaucomatous degeneration. J Neurosci, 2010. 30(16): 5644-5652.

24.  Crish SD, Sappington RM, Inman DM, Horner PJ, Calkins DJ. Distal axonopathy with structural persistence in glaucomatous neurodegeneration. Proc Natl Acad Sci U S A, 2010. 107(11): 5196-5201.

25.  Soto I, Oglesby E, Buckingham BP, Son JL, Roberson ED, Steele MR, Inman DM, Vetter ML, Horner PJ, Marsh-Armstrong N. Retinal ganglion cells downregulate gene expression and lose their axons within the optic nerve head in a mouse glaucoma model. J Neurosci, 2008. 28(2): 548-561.

26.  Liu X, Robinson ML, Schreiber AM, Wu V, Lavail MM, Cang J, Copenhagen DR. Regulation of neonatal development of retinal ganglion cell dendrites by neurotrophin-3 overexpression. J Comp Neurol, 2009. 514(5): 449-458.

27. Chen H, Liu X, Tian N. Subtype-dependent postnatal development of direction- and orientation-selective retinal ganglion cells in mice. J Neurophysiol, 2014. 112(9): 2092-2101.

28.  Thomson BR, Heinen S, Jeansson M, Ghosh AK, Fatima A, Sung HK, Onay T, Chen H, Yamaguchi S, Economides AN, Flenniken A, Gale NW, Hong YK, Fawzi A, Liu X, Kume T, Quaggin SE. A lymphatic defect causes ocular hypertension and glaucoma in mice. J Clin Invest, 2014. 124(10): 4320-4324.


____________

Conflict of interest: No conflicts declared.

* Corresponding Author. Xiaorong Liu: 847-467-0529; Hogan 2-160, 2205 Tech Drive, Northwestern University, Evanston, IL 60208, USA Email: xiaorong-liu@northwestern.edu

© 2015 by the Journal of Nature and Science (JNSCI).