For most neurodegenerative diseases the precise duration of an individual cell's death is unknown, which is an obstacle when counteractive measures are being considered. To address this, we used the rd1 mouse model for retinal neurodegeneration, characterized by phosphodiesterase-6 (PDE6) dysfunction and photoreceptor death triggered by high cyclic guanosine-mono-phosphate (cGMP) levels. Using cellular data on cGMP accumulation, cell death, and survival, we created mathematical models to simulate the temporal development of the degeneration. We validated model predictions using organotypic retinal explant cultures derived from wild-type animals and exposed to the selective PDE6 inhibitor zaprinast. Together, photoreceptor data and modeling for the first time delineated three major cell death phases in a complex neuronal tissue: (1) initiation, taking up to 36 h, (2) execution, lasting another 40 h, and finally (3) clearance, lasting about 7 h. Surprisingly, photoreceptor neurodegeneration was noticeably slower than necrosis or apoptosis, suggesting a different mechanism of death for these neurons.

Inherited retinal degeneration affecting both rod and cone photoreceptors constitutes one of the leading causes of blindness in the developed world. Such degeneration is at present untreatable, and the underlying neurodegenerative mechanisms are unknown, even though certain genetic causes have been established. The rd1 mouse is one of the best characterized animal models for rod photoreceptor degeneration, whereas the cpfl1 mouse is a recently discovered model for cone cell death. Because both animal models are affected by functionally similar mutations in the rod and cone phosphodiesterase 6 genes, respectively, we asked whether the mechanisms of photoreceptor degeneration in these two mouse lines share common pathways. In the present study, we followed the temporal progression of photoreceptor degeneration in the cpfl1 retina, correlated it with specific metabolic markers, and compared it with the wild-type and the rd1 situation. Similar to corresponding rd1 observations, cpfl1 cone photoreceptor cell death was associated with an accumulation of cyclic guanosine monophosphate (cGMP), activity of calpains, and phosphorylation of vasodilator-stimulated protein (VASP). Cone degeneration progressed rapidly, with a peak in cell death around postnatal day 24. Furthermore, cpfl1 cone photoreceptor migration during early postnatal development was delayed significantly compared with the corresponding wild-type retina. The finding that rod and cone photoreceptor degeneration was associated with the same metabolic markers suggests that in both cell types similar degenerative mechanisms are active. This raises the possibility that equivalent neuroprotective strategies may be used to prevent both rod and cone photoreceptor degeneration.

Sulforaphane (SFN), an isothiocyanate, is part of an important group of naturally occurring small molecules with anti-inflammatory properties. The published reports are best conceivable with an inhibition of T cell function, but the mode of action remains unknown. We therefore analyzed the effect of SFN on T cell–mediated autoimmune disease. Feeding mice with SFN protected from severe experimental autoimmune encephalomyelitis. Disease amelioration was associated with reduced IL-17 and IFN-γ expression in draining lymph nodes. In vitro, SFN treatment of T cells did not directly alter T cell cytokine secretion. In contrast, SFN treatment of dendritic cells (DCs) inhibited TLR4-induced IL-12 and IL-23 production, and severely suppressed Th1 and Th17 development of T cells primed by SFN-treated DCs. SFN regulated the activity of the TLR4-induced transcription factor NF-κB, without affecting the degradation of its inhibitor IκB-α. Instead, SFN treatment of DCs resulted in strong expression of the stress response protein heme oxygenase-1 (HO-1), which interacts with and thereby inhibits NF-κB p65. Consistent with these findings, HO-1 bound to p65 and subsequently inhibited the p65 activity at the IL23a and IL12b promoters. Importantly, SFN suppressed Il23a and Il12b expression in vivo and silenced Th17/Th1 responses within the CNS. Thus, our data show that SFN improves Th17/Th1-mediated autoimmune disease by inducing HO-1 and inhibiting NF-κB p65-regulated IL-23 and IL-12 expression.

Small interfering RNA (siRNA)-based therapies allow targeted correction of molecular defects in distinct cell populations. Although efficient in multiple cell populations, dendritic cells (DCs) seem to resist siRNA delivery. Using fluorescence labeling and radiolabeling, we show that cholesterol modification enables siRNA uptake by DCs in vitro and in vivo. Delivery of cholesterol-modified p40 siRNA selectively abolished p40 transcription and suppressed TLR-triggered p40 production by DCs. During immunization with peptide in CFA, cholesterol-modified p40 siRNA generated p40-deficient, IL-10-producing DCs that prevented IL-17/Th17 and IFN-g/Th1 responses. Only cholesterol-modified p40-siRNA established protective immunity against experimental autoimmune encephalomyelitis and suppressed IFN-g and IL-17 expression by CNS-infiltrating mononuclear cells without inducing regulatory T cells. Because cholesterol-modified siRNA can thus modify selected DC functions in vivo, it is intriguing for targeted immune therapy of allergic, autoimmune, or neoplastic diseases. The Journal of Immunology, 2015Immunology, , 195: 2216Immunology, -2223 T he RNA interference (RNAi) technology is established as efficient treatment strategy for various gene-targeted therapies. Because RNAi delivery to target cells has to be effective and safe, nonviral delivery systems and biochemical modifications are coming into major focus for targeting gene expression in vivo. The in vivo application of small interfering RNA (siRNA) requires structural modifications to improve serum stability and target tissue delivery. For instance, siRNA encapsulated by lipid nanoparticles facilitates siRNA delivery to hepatocytes followed by sequence-specific knockdown. Recently published clinical trials demonstrated first results on the efficacy of RNAi therapy in humans to correct metabolic disorders (1, 2). In contrast, the in vivo use of RNAi technologies for the therapy of inflammatory autoimmune diseases still faces major hurdles. For the successful delivery of RNAi in autoimmunity, the constructs should preferentially target immune cells without inducing major off-target effects. In addition, the constructs should not be immunogenic to minimize the risk for activating TLR and to avoid the induction of proinflammatory responses. One possibility to minimize off-target effects is the selection of a target gene preferentially expressed by immune cells. Therefore, we decided to focus on sequences that silence p40 (Il12b). As part of IL-12 and IL-23, p40 is mainly produced by dendritic cells (DCs) (3). DCs producing IL-12 and IL-23 are of central importance for the activation of autoreactive Th cells toward pathogenic Th1 and Th17 cells (4). Both of these Th cell subsets are crucially involved in the pathogenesis of numerous autoimmune diseases such as multiple sclerosis or psoriasis (5,6). Notably, the spontaneous uptake of siRNA by DCs is very limited and typically requires the use of transfection reagents (7), which cannot be applied in vivo. Also, the use of ...