KT-5823

Inherited retinal degeneration (IRD) is a debilitating condition characterized by progressive loss of photoreceptor cells. However, the underlying mechanisms remain largely unclear. This study investigated the role of DNA topoisomerase II alpha (TOP2A) and its interplay with protein kinase G (PKG) and histone deacetylase (HDAC) in the rd1 mouse model for IRD. Immunofluorescence and quantitative western blotting analyses were performed to evaluate the expression of TOP2A, PKG1, PKG2, HDAC1, and other related markers. TSC24 and suberoylanilide hydroxamic acid were used to specifically inhibit TOP2A and HDAC, respectively, in organotypic retinal explant cultures derived from wild‐type or rd1 mice. Furthermore, we examined the effect of PKG activity on TOP2A phosphorylation using KT5823. Significant upregulation of TOP2A was observed in the rd1 mouse retina compared with wild‐type controls, especially in the outer nuclear layer. Phosphorylation levels of TOP2A strongly correlated with photoreceptor cell death. Treatment with TSC24 significantly reduced TOP2A‐positive and TUNEL‐positive cells. TOP2A phosphorylation was accompanied by HDAC activation, which was mitigated by TSC24. PKG inhibition by KT5823 reduced TOP2A phosphorylation at specific residues and photoreceptor HDAC activity. Our findings position TOP2A in the PKG‐TOP2A‐HDAC photoreceptor degenerative pathway, offering new potential therapeutic targets for combating IRD‐type diseases.image

Phosphodiesterase inhibitors regulate intracellular Ca2+ of cardiomyocytes through enhancing second messenger signalling. This study aimed to investigate whether TP‐10, a selective phosphodiesterase10A inhibitor, modulates Ca2+ cycling, attenuating arrhythmogenesis in the right ventricular outflow tract (RVOT). Right ventricular tissues from New Zealand white rabbits were harvested, and electromechanical analyses of ventricular tissues were conducted. Intracellular Ca2+ was monitored using Fluo‐3, and ionic current was recorded using patch‐clamp in isolated cardiomyocytes. Tissues from RVOT exhibited a reduction in action potential duration at both 50% and 90% repolarisation following treatment with TP‐10. This treatment also inhibited burst firing induced by isoproterenol (ISO) in RVOT tissues, an effect that was nullified by thapsigargin. The protein kinase G inhibitor KT5823, whether used alone or in conjunction with TP‐10, also suppressed ISO‐induced burst firing in these tissues. Compared to the control group, RVOT cardiomyocytes treated with TP‐10 demonstrated enhanced amplitudes of Ca2+ transients and increased stores of Ca2+ in the sarcoplasmic reticulum. Although the L‐type Ca2+ current was diminished in TP‐10‐treated cardiomyocytes, the current from the Na+‐Ca2+ exchanger was elevated. Furthermore, the density of late Na+ current was significantly reduced in these treated cardiomyocytes. TP‐10 administration also resulted in increased levels of calcium regulatory proteins, specifically phosphorylated phospholamban at Thr17 and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2a. Our findings indicate that TP‐10 attenuates ISO‐induced arrhythmic events in RVOT tissues via cGMP‐mediated modulation of intracellular Ca2+ regulation.