Electroretinography in congenital nystagmus patients with a normal fundus examination.

PURPOSE: To identify the ophthalmic causes of congenital nystagmus with normal eye examination by electroretinography (ERG). STUDY DESIGN: Retrospective observational study. METHODS: We reviewed the medical records of patients younger than 6 months of age who presented between June 2008 and November 2011 with nystagmus and no other neurological signs following an otherwise normal eye examination. A complete ophthalmic examination and ERG (Nicolet Bravo system; Nicolet Biomedial & RETIscan; Roland Instruments), fundus photography, and Ishihara color test were performed to identify any ophthalmic causes of congenital nystagmus. RESULTS: Thirty-three patients met the criteria. Rod dysfunction was diagnosed in 4 patients (12.1%), cone dysfunction in 2 patients (6.1%), and cone-rod dysfunction in 1 patient (3.0%). The results of ERG were negative in 2 patients (6.1%). Idiopathic infantile nystagmus was diagnosed in the remaining 24 patients (72.7%) based on their normal ERG examination. CONCLUSIONS: In Korean congenital nystagmus patients with a normal fundus examination, achromatopsia and Leber's congenital amaurosis are uncommon causes. ERG is needed to make a definite diagnosis and provide prognostic information in congenital idiopathic nystagmus patients with a normal fundus examination.

Photobiomodulation therapy activates YAP and triggers proliferation and dedifferentiation of Müller glia in mammalian retina.

Photobiomodulation therapy has been proposed as a promising therapeutic approach for retinal degenerative diseases. However, its effect on the regenerative capacity in mammalian retina and its intracellular signalling mechanisms remain unknown. Here, we show that photobiomodulation with 670 nm light stimulates Müller glia cell cycle re-entry and dedifferentiation into a progenitor-like state in both the uninjured and injured retina. We also find that 670 nm light treatment inhibits the Hippo pathway, which is activated in Müller glia following NaIO3-induced retinal injury. YAP, a major downstream effector of the Hippo signalling pathway was translocated into the nucleus of Müller glia along with YAP dephosphorylation in retina treated with 670 nm light. Deficiency of YAP attenuated Müller glia cell cycle re-entry and dedifferentiation. Our data reveal that the Hippo-YAP signalling pathway is associated with the photostimulatory effect on regenerative response in mammalian retina, and suggest a potential therapeutic strategy for retinal degenerative diseases. [BMB Reports 2023; 56(9): 502-507].

Asp664 cleavage of amyloid precursor protein induces tau phosphorylation by decreasing protein phosphatase 2A activity.

Caspase cleavage of amyloid precursor protein (APP) has been reported to be important in amyloid beta protein (Aß)-mediated neurotoxicity. However, the underlying mechanisms are not clearly understood. In this study, we explored the effect of caspase cleavage of APP on tau phosphorylation in relation to Aß. We found that Asp664 cleavage of APP increased tau phosphorylation at Thr212 and Ser262 in N2A cells and primary cultured hippocampal neurons. Compared with wild-type APP, protein phosphatase 2A (PP2A) activity was significantly increased when Asp664 cleavage was blocked by the D664A point mutation. Furthermore, we found that over-expression of C31 reduced PP2A activity. C31 binds directly to the PP2A catalytic subunit, through the asparagine, proline, threonine, tyrosine (NPTY) motif, which is essential for C31-induced tau hyperphosphorylation. However, it appears that the other fragment produced by Asp664 cleavage, Jcasp, modulates neither PP2A activity nor tau hyperphosphorylation. Asp664 cleavage and accompanying tau hyperphosphorylation were remarkably diminished by blockage of Aß production using a γ-secretase inhibitor. Taken together, our results suggest that Asp664 cleavage of APP leads to tau hyperphosphorylation at specific epitopes by modulating PP2A activity as a downstream of Aß. Direct binding of C31 to PP2A through the C31-NPTY domain was identified as a mechanism underlying this effect.