title: Different effects of valproic acid on photoreceptor loss in Rd1 and Rd10 retinal degeneration mice.
abstract: OBJECTIVE
  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.
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Mitton
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Alvaro E
authors.initials: AE
authors.lastname: Guzman
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Mrinalini
authors.initials: M
authors.lastname: Deshpande
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: David
authors.initials: D
authors.lastname: Byrd
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Camryn
authors.initials: C
authors.lastname: DeLooff
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Kristina
authors.initials: K
authors.lastname: Mkoyan
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Paul
authors.initials: P
authors.lastname: Zlojutro
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Adrianne
authors.initials: A
authors.lastname: Wallace
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Brandon
authors.initials: B
authors.lastname: Metcalf
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Laux
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Jason
authors.initials: J
authors.lastname: Sotzen
authors.affiliation: Control of Gene Expression Laboratory and Pediatric Retinal Research Laboratory, Eye Research Institute, Oakland University, Rochester, MI.
authors.forename: Trung
authors.initials: T
authors.lastname: Tran
mesh_terms: D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics / Q000378:metabolism; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6 / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007274:Injections, Intraperitoneal; D064326:MEF2 Transcription Factors / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism; D057093:Orphan Nuclear Receptors / Q000235:genetics / Q000378:metabolism; D020011:Protective Agents / Q000494:pharmacology*; D012162:Retinal Degeneration / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014635:Valproic Acid / Q000494:pharmacology*
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D019208:Brain-Derived Neurotrophic Factor; D004791:Enzyme Inhibitors; D005136:Eye Proteins; D051100:Glial Cell Line-Derived Neurotrophic Factor; D018398:Homeodomain Proteins; D064326:MEF2 Transcription Factors; C578041:Mef2c protein, mouse; D009414:Nerve Growth Factors; C485736:Nr2e3 protein, mouse; C084884:Nrl protein, mouse; D057093:Orphan Nuclear Receptors; D020011:Protective Agents; D015534:Trans-Activators; C522218:cdnf protein, mouse; C109288:cone rod homeobox protein; D016222:Fibroblast Growth Factor 2; D014635:Valproic Acid; D012243:Rhodopsin; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; C517438:Pde6b protein, mouse