Qingjun Lu

Optic Neuropathy Induced by Experimentally Reduced Cerebrospinal Fluid Pressure in Monkeys

PURPOSEnTo examine the influence of experimentally reduced cerebrospinal fluid pressure (CSFP) on retinal nerve fiber layer (RNFL) thickness and neuroretinal rim area of the optic nerve head.nnnMETHODSnThis experimental study included nine monkeys that underwent implantation of a lumbar-peritoneal cerebrospinal fluid (CSF) shunt. In the study group (n = 4 monkeys), the shunt was opened to achieve a CSF of approximately 40 mm H2O, while the shunt remained closed in the control group (n = 5 monkeys). At baseline and in monthly intervals thereafter, optical coherence tomographic and photographic images of the optic nerve head and RNFL were taken of all monkeys.nnnRESULTSnTwo out of four monkeys in the study group showed bilaterally a progressive reduction in RNFL thickness between 12% and 30%, reduction in neuroretinal rim area and volume, and increase in cup-to-disc area ratios. A third monkey developed a splinter-like disc hemorrhage in one eye. The fourth monkey in the study group did not develop morphologic changes during follow-up, nor did any monkey in the control group.nnnCONCLUSIONSnExperimental and chronic reduction in CSF in monkeys was associated with the development of an optic neuropathy in some monkeys.

Enhanced protein expressions of sortilin and p75NTR in retina of rat following elevated intraocular pressure-induced retinal ischemia.

Elevated introcular pressure (IOP)-induced retinal neuron ischemic death includes an early phase of necrosis and prolonged phase of apoptosis. We used this ischemic model to observe the changes of sortilin and p75(NTR) protein expressions in rat retina. The results of Western blot analysis showed the expression of p75(NTR) at the band of 75 (mature form), 60 (non-glycosylated pieces) and 50 kDa (ectodomain shedding pieces), and the expression of sortilin at the 95 and 90 kDa (the mature form). The protein expressions of p75(NTR) (60 and 50 kDa pieces) and sortilin (90 kDa) increased significantly (p < 0.05) at days 3, 5 and 7 after retinal ischemia. This effect was also confirmed by immunofluorescence staining. Sortilin was primarily present in cell membrane of the ganglion cells layer (GCL) and large ganglion cell bodies by immunofluorescence labeling. There was little expression of p75(NTR) in the normal retina, while expression increased extensively in GCL, inner plexiform layer (IPL) and inner nuclear layer (INL) after retinal ischemia. p75(NTR) was shown to co-localize with neurofilament in the axons of neuronal cells by double-labeling. These results suggested that the protein expressions of 60 and 50 kDa forms of p75(NTR), and the 90 kDa mature form of sortilin increased in ischemia-induced retinal neuron of rats.

Immunohistochemical localization of sortilin and p75NTR in normal and ischemic rat retina

In our previous study, we found the increased expression of p75(NTR) and sortilin by Western blotting in ischemic retina induced by elevated intraocular pressure (IOP). Cell specific expression of sortilin and p75 neurotrophin receptor (p75(NTR)) was now characterized in normal and ischemic rat retina induced by elevated IOP by double-labeling immunochemistry. Two patterns of sortilin staining in normal retina were identified: punctate and consistent. The former was seen in the retinal ganglion cell (RGC) bodies, probably in Golgi apparatus. The latter was found in astrocytes and Müller glial cells (MGCs). The expression pattern of sortilin did not change in ischemic state induced by elevated IOP. p75(NTR) was not found in RGCs, but in MGCs of most of the retinal layers, especially the inner plexiform layer (IPL), and outer plexiform layer (OPL) of normal retina. Taken together, the enhanced expression of sortilin in MGCs might be involved in the neuro-glial interactions in ischemic retina, but may not directly contribute to RGCs death through proNGF binding to complex receptor composed of sortilin and p75(NTR) in ischemic retina.

Axonal Transport in the Rat Optic Nerve Following Short-Term Reduction in Cerebrospinal Fluid Pressure or Elevation in Intraocular Pressure

PURPOSEnTo examine the influence of short-term reduction in cerebrospinal fluid pressure (CSFP) as compared with short-term elevation in IOP on axonal transport.nnnMETHODSnThe study included 111 adult Sprague-Dawley rats. For 6 hours, IOP was unilaterally elevated to 40 mm Hg (IOP40-group; n = 27), IOP was unilaterally increased to a value of 25 mm Hg below the mean blood pressure (PP25-group; n = 27), or CSFP was reduced by continuous aspiration of cerebrospinal fluid (Low-CSFP-group; n = 27). A sham control group (with a trocar in cisterna magna without cerebrospinal fluid release) included 24 rats. The left eyes of the IOP40 study group and PP25 study group served as additional contralateral control group. Orthograde axonal transport was examined by intravitreally injected rhodamine-β-isothiocyanate; retrograde axoplasmic flow was assessed by fluorogold injected into the superior colliculi.nnnRESULTSnAt 24 hours after baseline, rhodamine-β-isothiocyanate (RITC) staining intensity of the optic nerve was lower (P < 0.05) in the IOP40-group, PP25-group, and Low-CSFP-group than in the control groups. At 6 hours after the fluorogold injection, fluorogold fluorescence was significantly lower in the IOP40-group, the PP25-group, and the Low-CSFP-group than in the control groups. At 5 days after baseline, the fluorogold fluorescence no longer differed significantly between the IOP40-group or the Low-CSFP-group and the control groups. At 1 week after baseline, retinal ganglion cell density was markedly reduced only in the PP25-group.nnnCONCLUSIONSnBoth short-term lowering of CSFP and short-term rise in IOP were associated with a disturbance of both the orthograde and retrograde axonal transport. The findings support the notion of an association between abnormally low CSFP and optic nerve damage.

Determination of conventional protein kinase C isoforms involved in high intraocular pressure-induced retinal ischemic preconditioning of rats

Evidence indicates that conventional protein kinase C (cPKC) plays a pivotal role in the development of retinal ischemic preconditioning (IPC). In this study, the effect of high intraocular pressure (IOP)-induced retinal IPC on cPKC isoform-specific membrane translocation and protein expression were observed. We found that cPKCgamma membrane translocation increased significantly at the early stage (20min-1h), while the protein expression levels of cPKCalpha and gamma were markedly elevated in the delayed retinal IPC (12-168h) of rats. The increased protein expressions of cPKCalpha at 72h and cPKCgamma at 24h after IPC were further confirmed by immunofluorescence staining. In addition, we found that cPKCgamma co-localized with retinal ganglion cell (RGC)-specific marker, neurofilaments heavy chain (NF-H) by using double immunofluorescence labeling. These results suggest that increased cPKCgamma membrane translocation and up-regulated protein expressions of cPKCalpha and gamma are involved in the development of high IOP-induced rat retinal IPC.

Apr3 accelerates the senescence of human retinal pigment epithelial cells

Senescence of retinal pigment epithelium (RPE) cells is a major contributor to age‑related macular degeneration (AMD). However, the molecular mechanisms underlying RPE dysfunction are not well understood. Apoptosis related protein 3 (Apr3) was originally cloned from HL‑60 cells induced by all‑trans retinoic acid (ATRA). Preliminary data revealed elevated Apr3 expression in the tissues of aged mice, suggesting that it is involved in the aging process. The present study demonstrated that Apr3 mRNA and protein levels were markedly increased in aged mouse RPE cells. Elevated Apr3 expression was also observed during premature senescence induced by oxidative stress (H2O2 and tert‑BHP) in ARPE‑19 cells. Moreover, Apr3 overexpression promoted cellular senescence in ARPE‑19 cells, as characterized by enhanced senescence‑associated β‑galactosidase activity, reduced cell proliferation and increased expression of the senescence markers p53 and p21. In addition, it was demonstrated that overexpression of Apr3‑N, a truncated counterpart of Apr3, abrogated Apr3‑induced phenotypes. It was concluded that Apr3 expression was induced in replicative and premature senescence of RPE cells and its overexpression accelerated senescence of ARPE‑19 cells, which provides important insights into the function of Apr3 in senescence‑associated diseases.

Author Response: Optic Neuropathy Secondary to Spontaneous Intracranial Hypotension (SIH) as Related to Experimental Primate Model

We thank Groth and colleagues for their interest in our study. The clinical situation presented by Groth and colleagues illustrated an optic disk–related optic neuropathy that may be partially similar to the optic neuropathy observed in the monkeys with experimentally low cerebrospinal fluid (CSF) pressure. It may be another example showing the potential importance of the CSF pressure as one determinant of the translaminar cribrosa pressure difference.