4c2f3060f034557ee71efa88d3e2dec0 pmc_34944588.pdf 290ff738bd33a069473d5b6d1d953193cbb97716 pmc_34944588.pdf 30d60a04adc3ab1d426701dd98e0f0806d5ff4008f222d2246dfb2b263466e6b pmc_34944588.pdf Title: Neuromodulation Induced by Sitagliptin: A New Strategy for Treating Diabetic Retinopathy Subject: Diabetic retinopathy (DR) involves progressive neurovascular degeneration of the retina. Reduction in synaptic protein expression has been observed in retinas from several diabetic animal models and human retinas. We previously reported that the topical administration (eye drops) of sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, prevented retinal neurodegeneration induced by diabetes in db/db mice. The aim of the present study is to examine whether the modulation of presynaptic proteins is a mechanism involved in the neuroprotective effect of sitagliptin. For this purpose, 12 db/db mice, aged 12 weeks, received a topical administration of sitagliptin (5 L; concentration: 10 mg/mL) twice per day for 2 weeks, while other 12 db/db mice were treated with vehicle (5 L). Twelve non-diabetic mice (db/+) were used as a control group. Protein levels were assessed by western blot and immunohistochemistry (IHC), and mRNA levels were evaluated by reverse transcription polymerase chain reaction (RT-PCR). Our results revealed a downregulation (protein and mRNA levels) of several presynaptic proteins such as synapsin I (Syn1), synaptophysin (Syp), synaptotagmin (Syt1), syntaxin 1A (Stx1a), vesicle-associated membrane protein 2 (Vamp2), and synaptosomal-associated protein of 25 kDa (Snap25) in diabetic mice treated with vehicle in comparison with non-diabetic mice. These proteins are involved in vesicle biogenesis, mobilization and docking, membrane fusion and recycling, and synaptic neurotransmission. Sitagliptin was able to significantly prevent the downregulation of all these proteins. We conclude that sitagliptin exerts beneficial effects in the retinas of db/db mice by preventing the downregulation of crucial presynaptic proteins. These neuroprotective effects open a new avenue for treating DR as well other retinal diseases in which neurodegeneration/synaptic abnormalities play a relevant role. Keywords: diabetic retinopathy; retinal neurodegeneration; dipeptidyl peptidase 4 inhibitors; sitagliptin; presynaptic proteins; db/db mouse model Author: Hugo Ramos, Patricia Bogdanov, David Sabater, Jordi Huerta, Marta Valeri, Cristina Hernández and Rafael Simó Creator: LaTeX with hyperref Producer: pdfTeX-1.40.21 CreationDate: Fri Nov 26 07:35:22 2021 CET ModDate: Fri Nov 26 07:51:05 2021 CET Custom Metadata: no Metadata Stream: no Tagged: no UserProperties: no Suspects: no Form: none JavaScript: no Pages: 16 Encrypted: no Page size: 595.276 x 841.89 pts (A4) Page rot: 0 File size: 4984274 bytes Optimized: no PDF version: 1.7 name type encoding emb sub uni object ID ------------------------------------ ----------------- ---------------- --- --- --- --------- ENXZUH+VnURWPalladioL-Bold Type 1 Custom yes yes no 10 0 VJAUGW+VnURWPalladioL Type 1 Custom yes yes no 15 0 OVNEXW+EURM10 Type 1 Builtin yes yes no 19 0 OZJRTK+URWPalladioL-Ital Type 1 Custom yes yes no 23 0 QLJJIR+URWPalladioL-Bold Type 1 Custom yes yes no 28 0 IZSBAO+URWPalladioL-Roma Type 1 Custom yes yes no 32 0 EBFBTV+TimesNewRomanPS-BoldItalicMT Type 1C WinAnsi yes yes no 40 0 MCBCCI+SourceSansRoman-Regular Type 1C Custom yes yes no 62 0 MCBCCM+SourceSansRoman.613wght Type 1C Custom yes yes no 66 0 MCBCCO+SourceSansRoman-Bold Type 1C Custom yes yes no 70 0 YFFKLH+CMSY10 Type 1 Builtin yes yes no 82 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 107 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 110 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 116 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 119 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 134 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 137 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 143 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 146 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 162 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 165 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 171 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 174 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 191 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 194 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 200 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 203 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 221 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 224 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 230 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 233 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 248 0 KMPPJP+PalatinoLinotype CID TrueType Identity-H yes yes yes 251 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 257 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 260 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 276 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 279 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 282 0 KMPPJO+PalatinoLinotype,Bold TrueType WinAnsi yes yes no 296 0 KMPPKA+PalatinoLinotype TrueType WinAnsi yes yes no 299 0 KMPPKC+PalatinoLinotype,Italic TrueType WinAnsi yes yes no 302 0 KNALAN+Calibri,Bold CID TrueType Identity-H yes yes yes 305 0 Jhove (Rel. 1.28.0, 2023-05-18) Date: 2024-10-02 03:37:43 CEST RepresentationInformation: pmc_34944588.pdf ReportingModule: PDF-hul, Rel. 1.12.4 (2023-03-16) LastModified: 2023-03-31 12:06:33 CEST Size: 4984274 Format: PDF Version: 1.7 Status: Well-Formed and valid SignatureMatches: PDF-hul MIMEtype: application/pdf PDFMetadata: Objects: 449 FreeObjects: 1 IncrementalUpdates: 0 DocumentCatalog: PageLayout: SinglePage PageMode: UseNone Outlines: Item: Title: Introduction Destination: section.1 Item: Title: Materials and Methods Destination: section.2 Children: Item: Title: Animals Destination: subsection.2.1 Item: Title: Topical Ocular Treatment Destination: subsection.2.2 Item: Title: Electroretinogram (ERG) Destination: subsection.2.3 Item: Title: Retinal Tissue Processing Destination: subsection.2.4 Children: Item: Title: RNA Extraction and Quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) Assay Destination: subsubsection.2.4.1 Item: Title: Western Blotting Destination: subsubsection.2.4.2 Item: Title: Immunofluorescence Analysis Destination: subsubsection.2.4.3 Item: Title: Statistical Analysis Destination: subsubsection.2.4.4 Item: Title: Results Destination: section.3 Item: Title: Discussion Destination: section.4 Item: Title: References Destination: section.4 Info: Title: Neuromodulation Induced by Sitagliptin: A New Strategy for Treating Diabetic Retinopathy Author: Hugo Ramos, Patricia Bogdanov, David Sabater, Jordi Huerta, Marta Valeri, Cristina Hernández and Rafael Simó Subject: Diabetic retinopathy (DR) involves progressive neurovascular degeneration of the retina. Reduction in synaptic protein expression has been observed in retinas from several diabetic animal models and human retinas. We previously reported that the topical administration (eye drops) of sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, prevented retinal neurodegeneration induced by diabetes in db/db mice. The aim of the present study is to examine whether the modulation of presynaptic proteins is a mechanism involved in the neuroprotective effect of sitagliptin. For this purpose, 12 db/db mice, aged 12 weeks, received a topical administration of sitagliptin (5 L; concentration: 10 mg/mL) twice per day for 2 weeks, while other 12 db/db mice were treated with vehicle (5 L). Twelve non-diabetic mice (db/+) were used as a control group. Protein levels were assessed by western blot and immunohistochemistry (IHC), and mRNA levels were evaluated by reverse transcription polymerase chain reaction (RT-PCR). Our results revealed a downregulation (protein and mRNA levels) of several presynaptic proteins such as synapsin I (Syn1), synaptophysin (Syp), synaptotagmin (Syt1), syntaxin 1A (Stx1a), vesicle-associated membrane protein 2 (Vamp2), and synaptosomal-associated protein of 25 kDa (Snap25) in diabetic mice treated with vehicle in comparison with non-diabetic mice. These proteins are involved in vesicle biogenesis, mobilization and docking, membrane fusion and recycling, and synaptic neurotransmission. Sitagliptin was able to significantly prevent the downregulation of all these proteins. We conclude that sitagliptin exerts beneficial effects in the retinas of db/db mice by preventing the downregulation of crucial presynaptic proteins. These neuroprotective effects open a new avenue for treating DR as well other retinal diseases in which neurodegeneration/synaptic abnormalities play a relevant role. Keywords: diabetic retinopathy; retinal neurodegeneration; dipeptidyl peptidase 4 inhibitors; sitagliptin; presynaptic proteins; db/db mouse model Creator: LaTeX with hyperref Producer: pdfTeX-1.40.21 CreationDate: Fri Nov 26 07:35:22 CET 2021 ModDate: Fri Nov 26 07:51:05 CET 2021 ID: 0xb80c62f8fb8f7a2811716b869d7e1ce9, 0xb80c62f8fb8f7a2811716b869d7e1ce9 Filters: FilterPipeline: FlateDecode Fonts: Type1: Font: BaseFont: IZSBAO+URWPalladioL-Roma FontSubset: true FirstChar: 2 LastChar: 246 FontDescriptor: FontName: IZSBAO+URWPalladioL-Roma Flags: Symbolic FontBBox: -166, -283, 1021, 943 FontFile: true EncodingDictionary: Differences: true Font: BaseFont: YFFKLH+CMSY10 FontSubset: true FirstChar: 0 LastChar: 48 FontDescriptor: FontName: YFFKLH+CMSY10 Flags: Symbolic FontBBox: -29, -960, 1116, 775 FontFile: true Font: BaseFont: OVNEXW+EURM10 FontSubset: true FirstChar: 22 LastChar: 22 FontDescriptor: FontName: OVNEXW+EURM10 Flags: Symbolic FontBBox: -32, -243, 1060, 720 FontFile: true 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