4 Early PrPSc accumulation associated with cone photoreceptor damage. Previously, our group and others found that prion-induced retinal damage to photoreceptor cells in mice and humans resembled pathology of human retinitis pigmentosa caused by mutations in retinal proteins. Here, using confocal, epifluorescent and electron microscopy we followed deposition of disease-associated prion protein (PrPSc) and its association with damage to critical retinal structures following intracerebral prion inoculation. The earliest time and place of cIAP1 Ligand-Linker Conjugates 12 retinal PrPSc deposition was 67?days post-inoculation (dpi) on the inner segment (IS) of cone photoreceptors. At 104 and 118 dpi, PrPSc was associated with the base of cilia cIAP1 Ligand-Linker Conjugates 12 and swollen cone inner segments, suggesting ciliopathy as a pathogenic mechanism. By 118 dpi, PrPSc was deposited in both rods and cones which showed rootlet damage in the IS, and photoreceptor cell death was indicated by thinning of the outer nuclear layer. In the outer plexiform layer (OPL) in uninfected mice, normal host PrP (PrPC) was mainly associated with cone bipolar cell processes, but cIAP1 Ligand-Linker Conjugates 12 in infected mice, at 118 dpi, PrPSc was detected on cone and rod bipolar cell dendrites extending into ribbon synapses. Loss of ribbon synapses in cone pedicles and rod spherules in the OPL was observed to precede destruction of most rods and cones over the next 2C3?weeks. However, bipolar cells and horizontal cells were less damaged, indicating high selectivity among neurons for injury by prions. PrPSc deposition in cIAP1 Ligand-Linker Conjugates 12 cone and rod inner segments and on the bipolar cell processes participating in ribbon synapses appear to be critical early events leading to damage and death of photoreceptors after prion infection.?These mechanisms may also occur in human retinitis pigmentosa and prion-like diseases, such as AD. not done aTimepoints are shown in days post inoculation (dpi) with 79A mouse adapted scrapie. In the 79A mouse-adapted scrapie model, mice begin showing clinical signs consistent with scrapie around 105-120dpi and reach clinical endpoint disease at approximately 160dpi. Thinning of the retina begins around 118dpi and likely causes blindness by the disease endpoint. bAntigens detected with antibodies described in Table ?Table11 cNumber of mice tested with each antibody at timepoint range shown dData not shown Nomenclature and detection of PrP, PrPC and PrPSc Monoclonal antibody D13 was used in immunostaining of tissue sections to detect PrP. In tissues of uninfected mice, PrP detected was assumed to be the normal PrP isoform, PrPC. In infected tissues, PrP detected in locations different from those seen uninfected mice was assumed to be disease-associated PrPSc, and PrP detected in similar locations to those found in uninfected mice was assumed to be either or both isoforms. Quantification of bipolar and horizontal cells To quantify rod bipolar cells throughout the timecourse of disease, two sections of retina from a mouse at each timepoint were stained with DAPI, anti-PKC primary antibody and secondary antibody Alexa Fluor 488 as described above. The PKC-positive rod bipolar cell bodies were counted in four 20X fields per timepoint and averaged. Horizontal TNFSF11 cell numbers were determined by staining retinal sections with DAPI, anti-calbindin primary antibody and Alexa Fluor 488 secondary antibody as described above. Calbindin-positive cell bodies were counted along two entire retinal sections from one mouse per timepoint. Cone bipolar cells were counted by staining retinal sections with anti-secretagogin antibody, which labels 8 of the 12 types of cone bipolar cells [13, 42] and.