Dynamin-Like Protein 1 Reduction Underlies Mitochondrial Morphology and Distribution Abnormalities in Fibroblasts from Sporadic Alzheimer's Disease Patients

Abstract

Mitochondrial function relies heavily on its morphology and distribution, alterations of which have been increasingly implicated in neurodegenerative diseases, such as Alzheimer's disease (AD). In this study, we found abnormal mitochondrial distribution characterized by elongated mitochondria that accumulated in perinuclear areas in 19.3% of sporadic AD (sAD) fibroblasts, which was in marked contrast to their normally even cytoplasmic distribution in the majority of human fibroblasts from normal subjects (>95%). Interestingly, levels of dynamin-like protein 1 (DLP1), a regulator of mitochondrial fission and distribution, were decreased significantly in sAD fibroblasts. To explore the potential role of DLP1 in mediating mitochondrial abnormalities in sAD fibroblasts, both the overexpression of a dominant negative DLP1 mutant and the reduced expression of DLP1 by miR RNAi in human fibroblasts from normal subjects significantly increased mitochondrial abnormalities. Moreover, overexpression of wild-type DLP1 in sAD fibroblasts rescued these mitochondrial abnormalities. Based on these data, we conclude that DLP1 reduction causes mitochondrial abnormalities in sAD fibroblasts. We further demonstrate that elevated oxidative stress and increased amyloid ␤ production are likely the potential pathogenic factors that cause DLP1 reduction and abnormal mitochondrial distribution in AD cells. Alzheimer's disease (AD) is the leading cause of dementia in the elderly, characterized by neurofibrillary tangles, senile plaques, and progressive loss of neuronal cells in selective brain regions.1 Whereas there are a myriad of striking alterations in the diseased brain, the pathogenesis of the disease is still currently poorly understood. Among these changes, oxidative stress is one of the earliest and may play a critical role in the disease. Mitochondria can be both targets of oxidative damage and sources of reactive oxygen species (ROS), and mitochondrial damage occurs during the aging process, 3 which is associated with memory loss. 4 In fact, damaged mitochondria are less efficient producers of ATP and more efficient producers of ROS. In AD, metabolic abnormalities 5 as well as damage to both the components and the structure of mitochondria are evident. 6 -8 Interestingly, quantitative morphometric studies not only confirm that neurons in AD demonstrate a higher percentage of damaged mitochondria but also reveal enlarged mitochondrial size with decreased mitochondria number in AD neurons. 2,9 The latter finding suggests that the normally strict regulation of mitochondria morphology is impaired, an assertion supported by work showing that AD cybrid cells also contain a significantly increased percentage of enlarged mitochondria. 10Mitochondrial morphology is dynamic and controlled by continual and balanced fission and fusion events that are regulated by a machinery involving large dynaminrelated GTPases that exert opposing effects, eg, dynamin-like protein 1 (DLP1, also referred to as Drp1, DVLP, dymple, HdynIV and DNM1P) [11][12...

Amyloid-β overproduction causes abnormal mitochondrial dynamics via differential modulation of mitochondrial fission/fusion proteins

“…However, suggestive of a dominant pathway, it is likely that DLP1 plays a major role in APP-induced abnormal mitochondrial distribution as the overexpression of DLP1, but not manipulations of OPA1 or Fis1, rescued perinuclear mitochondrial accumulation. Indeed, we recently reported a similar abnormal mitochondrial distribution as a prominent feature in AD fibroblasts that could also be rescued by overexpression of DLP1 (20). Because DLP1 failed to rescue APP-induced mitochondrial dysfunction (i.e., ROS, MMP, and ATP), it appears that the abnormal mitochondrial distribution had minimal impact on mitochondrial function parameters measured in this study; however, more subtle changes may not be ruled out.…”

“…However, as similar abnormalities in mitochondria are also evident features of fibroblasts from sporadic AD cases (20), it is likely that abnormal mitochondrial dynamics may be a feature of all AD cases, sporadic or familial. Such a notion is consistent with the decreased number but increased size of mitochondria in vulnerable neurons in the biopsied AD brain (9).…”

“…Human neuroblastoma M17 cells were grown as described before (36). Transfection was performed using Effectene (Qiagen) (20) and 300 g/ml geneticin (Invitrogen) or 400 g/ml of hygromycin B (Calbiochem) was included in the medium for stable cell line selection. Stable cell lines were maintained with 100 g/ml geneticin or 200 g/ml of hygromycin.…”

“…Impairments in mitochondrial dynamics are being increasingly implicated in neurodegenerative diseases (16). Very recently, we reported abnormal mitochondrial fission and fusion in AD fibroblasts (20). In this study, we aimed to determine whether APP and A␤ cause mitochondrial dysfunction and neuronal dysfunction through modulation of mitochondrial dynamics.…”

Altered mitochondrial dynamics as a consequence of Venezuelan Equine encephalitis virus infection

“…34 Interestingly, such a perinuclear clustering of mitochondria was also observed in fibroblasts obtained from Alzheimer's patients, suggestive of a relevance to neurodegenerative conditions. 35 We wanted to determine whether TC-83 infection led to alterations in the distribution of mitochondria in infected cells. TC-83 infected U87MG cells were processed for immunofluorescence analysis using anti-TOMM20 (mitochondrial membrane protein) and anti-VEEV capsid antibodies.…”