Alzheimer’s disease (AD) is the most prevalent neurodegenerative dementia in older adults worldwide. Sadly, there are no disease-modifying therapies available for treatment due to the multifactorial complexity of the disease. AD is pathologically characterized by extracellular deposition of amyloid beta (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. Increasing evidence suggest that Aβ also accumulates intracellularly, which may contribute to the pathological mitochondrial dysfunction observed in AD. According with the mitochondrial cascade hypothesis, mitochondrial dysfunction precedes clinical decline and thus targeting mitochondria may result in new therapeutic strategies. Unfortunately, the precise mechanisms connecting mitochondrial dysfunction with AD are largely unknown. In this review, we will discuss how the fruit fly Drosophila melanogaster is contributing to answer mechanistic questions in the field, from mitochondrial oxidative stress and calcium dysregulation to mitophagy and mitochondrial fusion and fission. In particular, we will highlight specific mitochondrial insults caused by Aβ and tau in transgenic flies and will also discuss a variety of genetic tools and sensors available to study mitochondrial biology in this flexible organism. Areas of opportunity and future directions will be also considered.

Background Alzheimer’s disease (AD) is a multifactorial neurodegenerative disorder characterized by dementia and cognitive decline due to progressive cerebral cortical atrophy. Brains of AD patients are characterized by the accumulation of microscopic extracellular amyloid‐beta (Aβ) plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. The deposition of Aβ42, which is one of the fragments of amyloid precursor protein (APP), has been known to play a role in initiating the events leading to the formation of amyloid and subsequently hyperphosphorylation of tau. However, animal models expressing either Aβ42 or tau individually do not mimic the complexity of the human condition. Indeed, recent evidence suggests that Aβ42 and pathological tau interact synergistically to modulate neurotoxicity in AD. Method To shed light on their concerted roles in AD pathogenesis and to discover pathways mediating Aβ42 and tau interactions, we generated transgenic flies co‐expressing human Aβ42 fused to a signal peptide along with the longest wild‐type tau isoform. Result Overexpression of Aβ42 or tau in Drosophila using the UAS‐Gal4 system causes mild to the moderate rough eye. In comparison, co‐expression of Aβ42 with tau causes severe roughening and reduction of the eye size. The level of neuronal cell death in eye tissues was also significantly enhanced in flies co‐expressing Aβ42 and tau. To identify pathways mediating Aβ42+tau interactions, we are currently using the Aβ42+tau eye phenotype as platform to screen 1,500 UAS lines expressing a variety of human genes. Conclusion We have identified few enhancers and suppressors not previously known to be involved in AD pathogenesis, which will be helpful to uncover new molecular pathways and potential therapeutic targets. This work is supported by NIH grant R21AG069050 to DERL.