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The late stage of dry age-related macular degeneration (AMD), or geographic atrophy (GA), is characterized by extensive retinal pigment epithelial (RPE) cell death, and a cure is not available currently. We have recently demonstrated that RPE cells die from necrosis in response to oxidative stress, providing a potential novel mechanism for RPE death in AMD. In this study, we screened U.S. Food and Drug Administration-approved natural compounds and identified gossypol acetic acid (GAA) as a potent inhibitor of oxidative stress-induced RPE cell death. GAA induces antioxidative response and inhibits accumulation of excessive reactive oxygen species in cells, through which it prevents the activation of intrinsic necrotic pathway in response to oxidative stress. Sestrin2 (SESN2) is found to mediate GAA function in antioxidative response and RPE survival upon oxidative stress. Moreover, Forkhead box O3 transcription factor (FoxO3) is further found to be required for GAA-mediated SESN2 expression and RPE survival. Mechanistically, GAA promotes FoxO3 nuclear translocation and binding to the SESN2 enhancer, which in turn increases its transcriptional activity. Taken together, we have identified GAA as a potent inhibitor of oxidative stress-induced RPE necrosis by regulating the FoxO3/SESN2 pathway. This study may have significant implications in the therapeutics of age-related diseases, especially GA.A ge-related macular degeneration (AMD) is the leading cause of severe vision loss in people aged over 50, and its prevalence increases exponentially in people over the age of 70 (1). Currently, it is estimated that 1.75 million individuals suffer from this disease in the United States, and 7 million are said to be "at risk" (2). There are two types of AMD, the "dry" and "wet" forms, respectively. Dry AMD is a chronic disease that usually causes some degree of visual impairment and sometimes progresses to severe blindness. Dry AMD accounts for 90% of AMD cases and is currently without treatment available. The late stage of dry AMD, which is also knows as geographic atrophy (GA), is characterized by scattered or confluent areas of degeneration of retinal pigment epithelium (RPE) cells and the overlying photoreceptors that rely on the RPE for trophic support (3). AMD is a multifactorial disease with unclear etiology. Age is the most consistent risk factor associated with AMD, and genetic factors, oxidative stress, and inflammation also significantly contribute to AMD pathogenesis (4). Cigarette smoking, which induces systemic oxidative stress, has been proved to be a significant risk factor for AMD. Consistently, clinical studies have shown that the progression of AMD can be slowed with antioxidant vitamins and zinc supplements (5, 6). The retina is one of the highest oxygen-consuming tissues in the human body and, in particular, RPE is vulnerable to oxidative damage (7,8). The mechanism of RPE cell death in response to oxidative stress and in GA has been controversial. Apoptosis was suggested as a major mechanism of RPE cell ...

The cellular basis of immunity to sporozoites was investigated by examining the effect of immunization of T and B cell-deficient C57BL/6N × BALB/c AnN F1 (BLCF1) mice compared to immunocompetent controls. Immunization of T cell-deficient (ATX-BM-ATS) BLCF1 mice with x-irradiated sporozoites did not result in the generation of protective immunity. The same immunization protocols protected all immunocompetent controls. In contrast, B cell-deficient (μ-suppressed) BLCF1 mice were protected by immunization in the majority of cases. The absence of detectable serum circumsporozoite precipitins or sporozoite neutralizing activity in the μ-suppressed mice that resisted a sporozoite challenge suggests a minor role for these humoral factors in protection. These data demonstrate a preeminent role for T cells in the induction of protective immunity in BLCF1 mice against a P. berghei sporozoite infection.