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Different effects of valproic acid on photoreceptor loss in Rd1 and Rd10 retinal degeneration mice.

Mitton KP, Guzman AE, Deshpande M, Byrd D, DeLooff C, Mkoyan K, Zlojutro P, Wallace A, Metcalf B, Laux K, Sotzen J, Tran T - Mol. Vis. (2014)

Bottom Line: Nrl gene expression was decreased by 50%, while Crx gene expression was not affected.Rod-specific expression of Mef2c and Nr2e3 was decreased substantially by VPA treatment, while Rhodopsin and Pde6b gene expression was normal at P28.While daily treatment with VPA could significantly reduce photoreceptor loss in the rd1 model, VPA treatment slightly accelerated photoreceptor loss in the rd10 model.

View Article: PubMed Central - PubMed

Affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.

ABSTRACT

Purpose: The histone-deacetylase inhibitor activity of valproic acid (VPA) was discovered after VPA's adoption as an anticonvulsant. This generated speculation for VPA's potential to increase the expression of neuroprotective genes. Clinical trials for retinitis pigmentosa (RP) are currently active, testing VPA's potential to reduce photoreceptor loss; however, we lack information regarding the effects of VPA on available mammalian models of retinal degeneration, nor do we know if retinal gene expression is perturbed by VPA in a predictable way. Thus, we examined the effects of systemic VPA on neurotrophic factor and Nrl-related gene expression in the mouse retina and compared VPA's effects on the rate of photoreceptor loss in two strains of mice, Pde6b(rd1/rd1) and Pde6b(rd10/rd10) .

Methods: The expression of Bdnf, Gdnf, Cntf, and Fgf2 was measured by quantitative PCR after single and multiple doses of VPA (intraperitoneal) in wild-type and Pde6b(rd1/rd1) mice. Pde6b(rd1/rd1) mice were treated with daily doses of VPA during the period of rapid photoreceptor loss. Pde6b(rd10/rd10) mice were also treated with systemic VPA to compare in a partial loss-of-function model. Retinal morphology was assessed by virtual microscopy or spectral-domain optical coherence tomography (SD-OCT). Full-field and focal electroretinography (ERG) analysis were employed with Pde6b(rd10/rd10) mice to measure retinal function.

Results: In wild-type postnatal mice, a single VPA dose increased the expression of Bdnf and Gdnf in the neural retina after 18 h, while the expression of Cntf was reduced by 70%. Daily dosing of wild-type mice from postnatal day P17 to P28 resulted in smaller increases in Bdnf and Gdnf expression, normal Cntf expression, and reduced Fgf2 expression (25%). Nrl gene expression was decreased by 50%, while Crx gene expression was not affected. Rod-specific expression of Mef2c and Nr2e3 was decreased substantially by VPA treatment, while Rhodopsin and Pde6b gene expression was normal at P28. Daily injections with VPA (P9-P21) dramatically slowed the loss of rod photoreceptors in Pde6b(rd1/rd1) mice. At age P21, VPA-treated mice had several extra rows of rod photoreceptor nuclei compared to PBS-injected littermates. Dosing started later (P14) or dosing every second day also rescued photoreceptors. In contrast, systemic VPA treatment of Pde6b(rd10/rd10) mice (P17-P28) reduced visual function that correlated with a slight increase in photoreceptor loss. Treating Pde6b(rd10/rd10) mice earlier (P9-P21) also failed to rescue photoreceptors. Treating wild-type mice earlier (P9-P21) reduced the number of photoreceptors in VPA-treated mice by 20% compared to PBS-treated animals.

Conclusions: A single systemic dose of VPA can change retinal neurotrophic factor and rod-specific gene expression in the immature retina. Daily VPA treatment from P17 to P28 can also alter gene expression in the mature neural retina. While daily treatment with VPA could significantly reduce photoreceptor loss in the rd1 model, VPA treatment slightly accelerated photoreceptor loss in the rd10 model. The apparent rescue of photoreceptors in the rd1 model was not the result of producing more photoreceptors before degeneration. In fact, daily systemic VPA was toxic to wild-type photoreceptors when started at P9. However, the effective treatment period for Pde6b(rd1/rd1) mice (P9-P21) has significant overlap with the photoreceptor maturation period, which complicates the use of the rd1 model for testing of VPA's efficacy. In contrast, VPA treatment started after P17 did not cause photoreceptor loss in wild-type mice. Thus, the acceleration of photoreceptor loss in the rd10 model may be more relevant where both photoreceptor loss and VPA treatment (P17-P28) started when the central retina was mature.

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Valproic acid (VPA) treatment using alternative dosing schedules started later or every second day reduced the rate of photoreceptor loss in Pde6brd1/rd1 mice. White arrows indicate the outer nuclear layer and regions shown at higher magnification (inserts). A: Daily VPA injections (350 mg/kg/day IP) started later from age P14 to P21. Two to three additional layers of photoreceptor cells (nuclei) remained in VPA-treated littermates compared to PBS-treated controls. B: VPA treatment with dosing every second day (350 mg/kg) and the treatment period starting later from age P14 to P21 also reduced the rate of photoreceptor loss (sections are paraffin, hematoxylin and eosin stained).
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f5: Valproic acid (VPA) treatment using alternative dosing schedules started later or every second day reduced the rate of photoreceptor loss in Pde6brd1/rd1 mice. White arrows indicate the outer nuclear layer and regions shown at higher magnification (inserts). A: Daily VPA injections (350 mg/kg/day IP) started later from age P14 to P21. Two to three additional layers of photoreceptor cells (nuclei) remained in VPA-treated littermates compared to PBS-treated controls. B: VPA treatment with dosing every second day (350 mg/kg) and the treatment period starting later from age P14 to P21 also reduced the rate of photoreceptor loss (sections are paraffin, hematoxylin and eosin stained).

Mentions: We also tested daily VPA treatment of Pde6brd1/rd1 mice starting later (P14 to P21), and dosing every second day (P14–P21). In both cases, we observed a reduction in photoreceptor loss for VPA-injected littermates compared to their PBS-injected littermates (Figure 5A,B), although these treatments were less effective than the daily VPA dosing from age P9 to P21.


Different effects of valproic acid on photoreceptor loss in Rd1 and Rd10 retinal degeneration mice.

Mitton KP, Guzman AE, Deshpande M, Byrd D, DeLooff C, Mkoyan K, Zlojutro P, Wallace A, Metcalf B, Laux K, Sotzen J, Tran T - Mol. Vis. (2014)

Valproic acid (VPA) treatment using alternative dosing schedules started later or every second day reduced the rate of photoreceptor loss in Pde6brd1/rd1 mice. White arrows indicate the outer nuclear layer and regions shown at higher magnification (inserts). A: Daily VPA injections (350 mg/kg/day IP) started later from age P14 to P21. Two to three additional layers of photoreceptor cells (nuclei) remained in VPA-treated littermates compared to PBS-treated controls. B: VPA treatment with dosing every second day (350 mg/kg) and the treatment period starting later from age P14 to P21 also reduced the rate of photoreceptor loss (sections are paraffin, hematoxylin and eosin stained).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4225157&req=5

f5: Valproic acid (VPA) treatment using alternative dosing schedules started later or every second day reduced the rate of photoreceptor loss in Pde6brd1/rd1 mice. White arrows indicate the outer nuclear layer and regions shown at higher magnification (inserts). A: Daily VPA injections (350 mg/kg/day IP) started later from age P14 to P21. Two to three additional layers of photoreceptor cells (nuclei) remained in VPA-treated littermates compared to PBS-treated controls. B: VPA treatment with dosing every second day (350 mg/kg) and the treatment period starting later from age P14 to P21 also reduced the rate of photoreceptor loss (sections are paraffin, hematoxylin and eosin stained).
Mentions: We also tested daily VPA treatment of Pde6brd1/rd1 mice starting later (P14 to P21), and dosing every second day (P14–P21). In both cases, we observed a reduction in photoreceptor loss for VPA-injected littermates compared to their PBS-injected littermates (Figure 5A,B), although these treatments were less effective than the daily VPA dosing from age P9 to P21.

Bottom Line: Nrl gene expression was decreased by 50%, while Crx gene expression was not affected.Rod-specific expression of Mef2c and Nr2e3 was decreased substantially by VPA treatment, while Rhodopsin and Pde6b gene expression was normal at P28.While daily treatment with VPA could significantly reduce photoreceptor loss in the rd1 model, VPA treatment slightly accelerated photoreceptor loss in the rd10 model.

View Article: PubMed Central - PubMed

Affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.

ABSTRACT

Purpose: The histone-deacetylase inhibitor activity of valproic acid (VPA) was discovered after VPA's adoption as an anticonvulsant. This generated speculation for VPA's potential to increase the expression of neuroprotective genes. Clinical trials for retinitis pigmentosa (RP) are currently active, testing VPA's potential to reduce photoreceptor loss; however, we lack information regarding the effects of VPA on available mammalian models of retinal degeneration, nor do we know if retinal gene expression is perturbed by VPA in a predictable way. Thus, we examined the effects of systemic VPA on neurotrophic factor and Nrl-related gene expression in the mouse retina and compared VPA's effects on the rate of photoreceptor loss in two strains of mice, Pde6b(rd1/rd1) and Pde6b(rd10/rd10) .

Methods: The expression of Bdnf, Gdnf, Cntf, and Fgf2 was measured by quantitative PCR after single and multiple doses of VPA (intraperitoneal) in wild-type and Pde6b(rd1/rd1) mice. Pde6b(rd1/rd1) mice were treated with daily doses of VPA during the period of rapid photoreceptor loss. Pde6b(rd10/rd10) mice were also treated with systemic VPA to compare in a partial loss-of-function model. Retinal morphology was assessed by virtual microscopy or spectral-domain optical coherence tomography (SD-OCT). Full-field and focal electroretinography (ERG) analysis were employed with Pde6b(rd10/rd10) mice to measure retinal function.

Results: In wild-type postnatal mice, a single VPA dose increased the expression of Bdnf and Gdnf in the neural retina after 18 h, while the expression of Cntf was reduced by 70%. Daily dosing of wild-type mice from postnatal day P17 to P28 resulted in smaller increases in Bdnf and Gdnf expression, normal Cntf expression, and reduced Fgf2 expression (25%). Nrl gene expression was decreased by 50%, while Crx gene expression was not affected. Rod-specific expression of Mef2c and Nr2e3 was decreased substantially by VPA treatment, while Rhodopsin and Pde6b gene expression was normal at P28. Daily injections with VPA (P9-P21) dramatically slowed the loss of rod photoreceptors in Pde6b(rd1/rd1) mice. At age P21, VPA-treated mice had several extra rows of rod photoreceptor nuclei compared to PBS-injected littermates. Dosing started later (P14) or dosing every second day also rescued photoreceptors. In contrast, systemic VPA treatment of Pde6b(rd10/rd10) mice (P17-P28) reduced visual function that correlated with a slight increase in photoreceptor loss. Treating Pde6b(rd10/rd10) mice earlier (P9-P21) also failed to rescue photoreceptors. Treating wild-type mice earlier (P9-P21) reduced the number of photoreceptors in VPA-treated mice by 20% compared to PBS-treated animals.

Conclusions: A single systemic dose of VPA can change retinal neurotrophic factor and rod-specific gene expression in the immature retina. Daily VPA treatment from P17 to P28 can also alter gene expression in the mature neural retina. While daily treatment with VPA could significantly reduce photoreceptor loss in the rd1 model, VPA treatment slightly accelerated photoreceptor loss in the rd10 model. The apparent rescue of photoreceptors in the rd1 model was not the result of producing more photoreceptors before degeneration. In fact, daily systemic VPA was toxic to wild-type photoreceptors when started at P9. However, the effective treatment period for Pde6b(rd1/rd1) mice (P9-P21) has significant overlap with the photoreceptor maturation period, which complicates the use of the rd1 model for testing of VPA's efficacy. In contrast, VPA treatment started after P17 did not cause photoreceptor loss in wild-type mice. Thus, the acceleration of photoreceptor loss in the rd10 model may be more relevant where both photoreceptor loss and VPA treatment (P17-P28) started when the central retina was mature.

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Related in: MedlinePlus