Pelargonidin protects retinal ganglion cells in a streptozotocin-induced diabetic rat model by reducing intraocular pressure, suppressing TGF-β and activating JAK2/STAT3 signalling pathway.

Diabetic retinopathy (DR) is one of the primary causes of vision impairment, affecting individuals with diabetes, and is marked by the neurodegeneration of the retina along with increased intraocular pressure (IOP). This study sought to determine the effects of pelargonidin on extracellular matrix (ECM) modulation and the inhibition of transforming growth factor-β (TGF-β) and Janus Kinase 2/Signal Transducer and Activator of Transcription 3 (JAK2/STAT3) pathway in retinal ganglion cells of streptozotocin-induced diabetic rats. Male Sprague-Dawley rats (180-200 g) were rendered diabetic by intraperitoneal administration of streptozotocin (STZ). The rats were divided into 5 groups: control, diabetic model (STZ), STZ + low dose pelargonidin (12.5 mg kg^-1 per day), STZ + medium dose pelargonidin (25 mg kg-1 per day) and STZ + high dose pelargonidin (50 mg kg^-1 per day). IOP was monitored using a tonometer. Whole-mount retinal immunofluorescence staining using RNA-binding protein with multiple splicing (RBPMS) was performed to assess retinal ganglion cell (RGC) density. Protein expression levels of apoptotic markers, ECM components, and TGF-β and JAK2/STAT3 signalling pathways were evaluated by Western blotting. Pelargonidin treatment dose-dependently reduced the elevated IOP. Importantly, immunofluorescence analysis revealed a marked dose-dependent preservation of retinal ganglion cell (RGC) density: STZ-induced RGC loss was significantly reversed by pelargonidin, with the highest dose restoring RGC density to near-control or higher levels in both the central and peripheral retina. This was achieved via modulation of apoptosis-related proteins through the upregulation of Bcl-xL, Bcl-2, and downregulation of Bad, Bax and cleaved caspase-3. Furthermore, pelargonidin modulated ECM remodelling protein expression in the RGC layer. In particular, TGF-β2/Smad2/3 signalling was downregulated, and the JAK2/STAT3 pathway was upregulated. By reducing IOP, preserving RGC density, modulating ECM deposition, inhibiting TGF-β and upregulating the JAK2/STAT3 pathway, pelargonidin exerts protective effects against diabetic retinal injury. The results of this study further confirm the pharmacological potential of pelargonidin as a therapeutic agent for diabetic retinopathy.