Limits...
Loss of Ikbkap Causes Slow, Progressive Retinal Degeneration in a Mouse Model of Familial Dysautonomia

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy that is caused by a mutation in the gene for inhibitor of kappa B kinase complex-associated protein (IKBKAP). Although FD patients suffer from multiple neuropathies, a major debilitation that affects their quality of life is progressive blindness. To determine the requirement for Ikbkap in the developing and adult retina, we generated Ikbkap conditional knockout (CKO) mice using a TUBA1a promoter-Cre (Tα1-Cre). In the retina, Tα1-Cre expression is detected predominantly in retinal ganglion cells (RGCs). At 6 months, significant loss of RGCs had occurred in the CKO retinas, with the greatest loss in the temporal retina, which is the same spatial phenotype observed in FD, Leber hereditary optic neuropathy, and dominant optic atrophy. Interestingly, the melanopsin-positive RGCs were resistant to degeneration. By 9 months, signs of photoreceptor degeneration were observed, which later progressed to panretinal degeneration, including RGC and photoreceptor loss, optic nerve thinning, Müller glial activation, and disruption of layers. Taking these results together, we conclude that although Ikbkap is not required for normal development of RGCs, its loss causes a slow, progressive RGC degeneration most severely in the temporal retina, which is later followed by indirect photoreceptor loss and complete retinal disorganization. This mouse model of FD is not only useful for identifying the mechanisms mediating retinal degeneration, but also provides a model system in which to attempt to test therapeutics that may mitigate the loss of vision in FD patients.

No MeSH data available.


Related in: MedlinePlus

Photoreceptor degeneration was observed in Ikbkap CKO retinas. The number of rows of photoreceptor nuclei in the ONL was counted at 0.25 mm from the optic nerve in the temporal and nasal retinas at 6 months (A), 9 months (C), and 14 months (E). H&E-stained cross sections. A and B, At 6 months, no sign of photoreceptor degeneration was observed. C and D, At 9 months, significant loss of photoreceptors and disorganization of ONL (arrowheads) in the mutant temporal and peripheral retinas were observed. E and F, At 14 months, the number of rows of photoreceptor nuclei was clearly reduced across the retina. In addition, photoreceptor IS and OS were absent. Error bars in A, C, and E represent SEM (*p < 0.05 with t-test). Scale bars, 50 μm (B, D, and F).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5037323&req=5

Figure 8: Photoreceptor degeneration was observed in Ikbkap CKO retinas. The number of rows of photoreceptor nuclei in the ONL was counted at 0.25 mm from the optic nerve in the temporal and nasal retinas at 6 months (A), 9 months (C), and 14 months (E). H&E-stained cross sections. A and B, At 6 months, no sign of photoreceptor degeneration was observed. C and D, At 9 months, significant loss of photoreceptors and disorganization of ONL (arrowheads) in the mutant temporal and peripheral retinas were observed. E and F, At 14 months, the number of rows of photoreceptor nuclei was clearly reduced across the retina. In addition, photoreceptor IS and OS were absent. Error bars in A, C, and E represent SEM (*p < 0.05 with t-test). Scale bars, 50 μm (B, D, and F).

Mentions: Because older mutant retinas show clear signs of photoreceptor degeneration (Fig. 3), we quantified the number of photoreceptors in 6-, 9-, and 14-month mutant and control retinas (Fig. 8). The number of photoreceptors lying in a single column spanning the ONL was counted in H&E-stained retinal cross sections as described previously (LaVail et al., 1992; Ueki et al., 2008; Chollangi et al., 2009). Counts were made at 0.25-mm intervals beginning at the ONH and toward both the temporal and nasal retinal hemispheres (Fig. 8A, C, E). At 6 months, mutant retinas had similar numbers of rows of photoreceptor nuclei in the ONL across the retina, and photoreceptor IS and OS showed normal morphology (Fig. 8A, B). By 9 months, the temporal retina of the mutants showed slight but significant reduction in photoreceptor nuclei, indicative of photoreceptor degeneration (Fig. 8C). We also observed dyslamination of ONL at temporal peripheral (>1.5 mm from ONH) retinas of mutants, with the ectopic presence of photoreceptor nuclei in the outer plexiform layer (Fig. 8D, arrowheads). By 14 months, panretinal photoreceptor degeneration was observed: on average, the number of rows of photoreceptor nuclei was reduced by 30%–40% across mutant retinas compared with controls (Fig. 8E). The extent of photoreceptor loss varied between mutants, and some mutant retinas displayed severe photoreceptor degeneration with no IS and OS (Fig. 8F). We speculate that this photoreceptor degeneration in our Ikbkap CKO retinas is an indirect consequence of Ikbkap loss in cell types other than photoreceptors, since Tα1-Cre expression is nearly absent in photoreceptors in both young and older retinas (Fig. 2A, K).


Loss of Ikbkap Causes Slow, Progressive Retinal Degeneration in a Mouse Model of Familial Dysautonomia
Photoreceptor degeneration was observed in Ikbkap CKO retinas. The number of rows of photoreceptor nuclei in the ONL was counted at 0.25 mm from the optic nerve in the temporal and nasal retinas at 6 months (A), 9 months (C), and 14 months (E). H&E-stained cross sections. A and B, At 6 months, no sign of photoreceptor degeneration was observed. C and D, At 9 months, significant loss of photoreceptors and disorganization of ONL (arrowheads) in the mutant temporal and peripheral retinas were observed. E and F, At 14 months, the number of rows of photoreceptor nuclei was clearly reduced across the retina. In addition, photoreceptor IS and OS were absent. Error bars in A, C, and E represent SEM (*p < 0.05 with t-test). Scale bars, 50 μm (B, D, and F).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037323&req=5

Figure 8: Photoreceptor degeneration was observed in Ikbkap CKO retinas. The number of rows of photoreceptor nuclei in the ONL was counted at 0.25 mm from the optic nerve in the temporal and nasal retinas at 6 months (A), 9 months (C), and 14 months (E). H&E-stained cross sections. A and B, At 6 months, no sign of photoreceptor degeneration was observed. C and D, At 9 months, significant loss of photoreceptors and disorganization of ONL (arrowheads) in the mutant temporal and peripheral retinas were observed. E and F, At 14 months, the number of rows of photoreceptor nuclei was clearly reduced across the retina. In addition, photoreceptor IS and OS were absent. Error bars in A, C, and E represent SEM (*p < 0.05 with t-test). Scale bars, 50 μm (B, D, and F).
Mentions: Because older mutant retinas show clear signs of photoreceptor degeneration (Fig. 3), we quantified the number of photoreceptors in 6-, 9-, and 14-month mutant and control retinas (Fig. 8). The number of photoreceptors lying in a single column spanning the ONL was counted in H&E-stained retinal cross sections as described previously (LaVail et al., 1992; Ueki et al., 2008; Chollangi et al., 2009). Counts were made at 0.25-mm intervals beginning at the ONH and toward both the temporal and nasal retinal hemispheres (Fig. 8A, C, E). At 6 months, mutant retinas had similar numbers of rows of photoreceptor nuclei in the ONL across the retina, and photoreceptor IS and OS showed normal morphology (Fig. 8A, B). By 9 months, the temporal retina of the mutants showed slight but significant reduction in photoreceptor nuclei, indicative of photoreceptor degeneration (Fig. 8C). We also observed dyslamination of ONL at temporal peripheral (>1.5 mm from ONH) retinas of mutants, with the ectopic presence of photoreceptor nuclei in the outer plexiform layer (Fig. 8D, arrowheads). By 14 months, panretinal photoreceptor degeneration was observed: on average, the number of rows of photoreceptor nuclei was reduced by 30%–40% across mutant retinas compared with controls (Fig. 8E). The extent of photoreceptor loss varied between mutants, and some mutant retinas displayed severe photoreceptor degeneration with no IS and OS (Fig. 8F). We speculate that this photoreceptor degeneration in our Ikbkap CKO retinas is an indirect consequence of Ikbkap loss in cell types other than photoreceptors, since Tα1-Cre expression is nearly absent in photoreceptors in both young and older retinas (Fig. 2A, K).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy that is caused by a mutation in the gene for inhibitor of kappa B kinase complex-associated protein (IKBKAP). Although FD patients suffer from multiple neuropathies, a major debilitation that affects their quality of life is progressive blindness. To determine the requirement for Ikbkap in the developing and adult retina, we generated Ikbkap conditional knockout (CKO) mice using a TUBA1a promoter-Cre (T&alpha;1-Cre). In the retina, T&alpha;1-Cre expression is detected predominantly in retinal ganglion cells (RGCs). At 6 months, significant loss of RGCs had occurred in the CKO retinas, with the greatest loss in the temporal retina, which is the same spatial phenotype observed in FD, Leber hereditary optic neuropathy, and dominant optic atrophy. Interestingly, the melanopsin-positive RGCs were resistant to degeneration. By 9 months, signs of photoreceptor degeneration were observed, which later progressed to panretinal degeneration, including RGC and photoreceptor loss, optic nerve thinning, M&uuml;ller glial activation, and disruption of layers. Taking these results together, we conclude that although Ikbkap is not required for normal development of RGCs, its loss causes a slow, progressive RGC degeneration most severely in the temporal retina, which is later followed by indirect photoreceptor loss and complete retinal disorganization. This mouse model of FD is not only useful for identifying the mechanisms mediating retinal degeneration, but also provides a model system in which to attempt to test therapeutics that may mitigate the loss of vision in FD patients.

No MeSH data available.


Related in: MedlinePlus