Alzheimer's disease (AD) is the most common form of age-related dementia, characterized by progressive memory loss and cognitive disturbance. Mutations of presenilin 1 (PS1) and presenilin 2 (PS2) are causative factors for autosomal-dominant early-onset familial AD (FAD). Induced pluripotent stem cell (iPSC) technology can be used to model human disorders and provide novel opportunities to study cellular mechanisms and establish therapeutic strategies against various diseases, including neurodegenerative diseases. Here we generate iPSCs from fibroblasts of FAD patients with mutations in PS1 (A246E) and PS2 (N141I), and characterize the differentiation of these cells into neurons. We find that FAD–iPSC-derived differentiated neurons have increased amyloid β42 secretion, recapitulating the molecular pathogenesis of mutant presenilins. Furthermore, secretion of amyloid β42 from these neurons sharply responds to γ-secretase inhibitors and modulators, indicating the potential for identification and validation of candidate drugs. Our findings demonstrate that the FAD-iPSC-derived neuron is a valid model of AD and provides an innovative strategy for the study of age-related neurodegenerative diseases.

Background and Purpose —Iba1 is a novel calcium-binding protein and is specifically expressed in microglia in the brain. It has been suggested that Iba1 plays an important role in regulation of the function of microglia. In the present study we examined time-dependent Iba1 expression after transient middle cerebral artery occlusion and characterized microglial activation in various brain regions. Methods —Rat middle cerebral artery occlusion was induced by the intraluminal filament technique. After 1.5 hours of transient ischemia, Iba1 expression was examined by immunohistochemical and immunoblot analyses. The microglial activation in association with ischemic severity was characterized by double immunostaining with other specific markers. Results —In the peri-ischemic area, heavily Iba1 immunoreactive cells rapidly appeared at 3.5 hours after reperfusion. Immunoreactivity was further increased and peaked at 7 days. In the ischemic core, round Iba1-positive cells, which may be blood-borne monocytes, appeared from 24 hours and reached a peak at 4 to 7 days. Double immunostaining revealed that activated microglia in the peri-ischemic area upregulated Iba1 expression but were negative for the macrophage marker ED1. ED1-positive cells were clearly restricted to the ischemic core. Conclusions —These findings suggest the following: (1) Iba1 expression may be associated with microglial activation in ischemic brain, and Iba1 immunostaining can be useful to evaluate the pathophysiological roles of activated microglia in ischemic injury. (2) Expression of ED1 antigen is strictly restricted to severe ischemic damage, whereas activated microglia in the peri-ischemic area showed Iba1 upregulation without ED1. Therefore, microglia may exhibit difference of antigenicity in the severity of ischemic brain injury.

Background: Parkinson’s disease (PD) is a neurodegenerative disease characterized by selective degeneration of dopaminergic neurons in the substantia nigra (SN). The familial form of PD, PARK2, is caused by mutations in the parkin gene. parkin-knockout mouse models show some abnormalities, but they do not fully recapitulate the pathophysiology of human PARK2. Results: Here, we generated induced pluripotent stem cells (iPSCs) from two PARK2 patients. PARK2 iPSC-derived neurons showed increased oxidative stress and enhanced activity of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. iPSC-derived neurons, but not fibroblasts or iPSCs, exhibited abnormal mitochondrial morphology and impaired mitochondrial homeostasis. Although PARK2 patients rarely exhibit Lewy body (LB) formation with an accumulation of α-synuclein, α-synuclein accumulation was observed in the postmortem brain of one of the donor patients. This accumulation was also seen in the iPSC-derived neurons in the same patient. Conclusions: Thus, pathogenic changes in the brain of a PARK2 patient were recapitulated using iPSC technology. These novel findings reveal mechanistic insights into the onset of PARK2 and identify novel targets for drug screening and potential modified therapies for PD.

The tumor suppressor BRCA1 contains multiple functional domains that interact with many proteins. After DNA damage, BRCA1 is phosphorylated by CHK2 at serine 988, followed by a change in its intracellular location. To study the functions of CHK2-dependent phosphorylation of BRCA1, we generated a mouse model carrying the mutation S971A (S971 in mouse Brca1 corresponds to S988 in human BRCA1) by gene targeting. Brca1^S971A/S971A mice were born at the expected ratio without a developmental defect, unlike previously reported Brca1 mutant mice. However, Brca1^S971A/S971A mice suffered a moderately increased risk of spontaneous tumor formation, with a majority of females developing uterus hyperplasia and ovarian abnormalities by 2 years of age. After treatment with DNA-damaging agents, Brca1^S971A/S971A mice exhibited several abnormalities, including increased body weight, abnormal hair growth pattern, lymphoma, mammary tumors, and endometrial tumors. In addition, the onset of tumor formation became accelerated, and 80% of the mutant mice had developed tumors by 1 year of age. We demonstrated that the Brca1^S971A/S971A cells displayed reduced ability to activate the G₂/M cell cycle checkpoint upon γ-irradiation and to stabilize p53 following N-methyl-N′-nitro-N-nitrosoguanidine treatment. These observations suggest that Chk2 phosphorylation of S971 is involved in Brca1 function in modulating the DNA damage response and repressing tumor formation.