Wenzhang Wang, Ph.D. - US grants

Mitochondria are involved in key cellular processes such as energy supply and calcium buffering critical for neuronal function. It is known that mitochondria are constantly facing various stresses under both physiological and pathological conditions which pose great challenge for the maintenance of mitochondrial homeostasis. As dynamic organelles in cells, mitochondria are continually undergoing fusion and fission to maintain a healthy mitochondrial pool. In addition, mitochondria homeostasis also relies on quality control system of mitochondrial proteostasis. It is well established that mitochondrial chaperones and ATP-dependent proteases form a complex and functionally interconnected system to monitor damaged proteins: mitochondrial chaperones are involved in protein translocation and folding reactions while ATP-dependent proteases are responsible for directly removing misfolded proteins from mitochondria. Increasing evidence demonstrated that defects in mitochondrial protease and chaperones cause mitochondrial dysfunction and have been associated with human diseases especially neurological disorders. In this regard, it is of importance to note that mitochondrial abnormality is an early prominent feature in Alzheimer?s disease (AD) and increasing evidence suggest that mitochondrial dysfunction plays a critical role in the pathogenesis of AD. However, mechanisms underlying mitochondrial dysfunction in AD remain elusive. To explore the potential involvement of an altered mitochondrial quality control system in the pathogenesis of AD, we undertook a pilot study to determine whether there is any change in the expression of mitochondrial chaperones and proteases in AD. Indeed, we found significantly decreased expression of mitochondrial matrix proteases (i.e., CLLP and LONP1) in AD brain tissues. More importantly, ultrastructure analysis of biopsy human brain samples uncovered increased mitochondrial electron dense inclusions, likely aggregations of misfolded proteins, in mitochondria in the susceptible neurons of AD cortex. These data suggested an impaired mitochondrial quality control system in AD. Our in vitro experiments demonstrated that amyloid-beta (A?) inhibits the activity of mitochondrial protease complexes. Interestingly, overexpression of mitochondrial proteases could rescue mitochondrial respiration deficits in primary neuron from CRND8 mice, an APP transgenic mouse model for AD. Based on these exciting preliminary data, we hypothesize that A? induces abnormal mitochondrial proteostasis by impairing the activity of mitochondrial proteases and further causes mitochondrial dysfunction and neuronal loss in AD. To test this hypothesis, we will characterize the causal role of A?-induced abnormal mitochondrial proteostasis in the pathogenesis of AD both in vivo and in vitro which will likely provide novel therapeutic targets of the disease.

Abstract Neurodegeneration in brain with iron accumulation (NBIA) defines a group of rare hereditary diseases with prominent features of iron deposition and related neuronal loss in the nervous system. Although significant progress in the genetic studies uncovered the essential role of mitochondrial dysfunction in the pathogenesis of NBIA, the underlying mechanism of mitochondrial abnormality and metal dysregulation in NBIA remains elusive. In this regard, we focused on the mitochondrial membrane proteins associated iron accumulation (MPAN) that was caused by genetic mutations in C19orf12, a protein with unknown function. In the pilot study, we analyzed human biopsy of an MPAN case, mouse brain tissue and human neuroblastoma M17 cell lines with C19orf12 knock-out (KO) to explore the role of C19orf12 in the mitochondria of MPAN and also in the normal mitochondria. Indeed, our preliminary data of imaging investigation on brain biopsy of MPAN conditions suggested mitochondria are impaired in the surviving neurons, which underscored the mitochondrial dysfunction in MPAN. The exploration of C19orf12 in vivo showed the mitochondrial localization and protein expression of C19orf12 in mouse brain tissues. Importantly, we found that C19orf12 is associated with mitochondrial complex IV of the electron transfer chain in vivo. In vitro study of C19orf12, mitochondrial respiration analysis of C19orf12 KO M17 cells showed impaired mitochondrial oxygen consumption in vitro. Furthermore, trace metal analysis showed both iron and copper dysregulation in the mitochondria of C19orf12 KO cells. Taken together, this exciting data demonstrated that the critical role of C19orf12 in mitochondrial function and metal regulation in the physiological condition and the likely related disturbance of C19orf12 during the pathogenesis of MPAN. Therefore, the further study to explore the mechanism of metal regulation in MPAN and how C19orf12 mutants impair mitochondrial function is warranted. The current application will shed light on the novel mechanism of C19orf12 that is linking mitochondrial dysfunction and metal dysregulation in the MPAN pathology.

PROJECT SUMMARY/ABSTRACT Mitochondrial deficits is one of the early and prominent features of Alzheimer?s disease and a large body of studies suggest mitochondrial dysfunction could trigger the pathogenesis of AD. However, the underlying mechanism remains elusive. Recent progress in mitochondrial studies highlight the unique mitochondrial structural system and its implication under both physiological and pathological conditions. In particular, it is well known that mitochondrial inner membrane connects outer membrane by the individual contact site, which forms neck-like tubule to communicate inter-membrane space and intra-cristae space. A growing body of studies unveiled the molecular machinery in maintaining the integrity of mitochondria by the mitochondrial contact site and cristae organizing system (MICOS). It is not surprising that impaired MICOS greatly deteriorates mitochondrial morphology and function. Importantly, abnormal MICOS is associated with several human diseases including nervous diseases, which underscores the significance of analyzing the MICOS in the most prevalent neurodegenerative disease in the world. In this regard, we investigated the integrity of MICOS in human brains of AD and control cases. Our preliminary data suggest there were changes of MICOS related mitochondrial cristae structure in the cortical neurons of human AD brains by electron microscopy analysis. In addition, there were deficits in proteins levels, neuronal distributions of core MICSOS components and assembly of MICOS complex in human AD brains in the pilot study. Altogether, both structural and biochemical analysis suggested the impaired MICOS in AD brain. These exciting discoveries raised a critical question of whether and how impaired neuronal MICOS contributed to the mitochondrial dysfunction and neuronal loss in the AD. In this application, as the first step to characterize the potential role of abnormal MICOS changes in mitochondrial dysfunction and pathogenesis of AD, we will explore the changes of MICOS and its consequences and correlation with other mitochondrial/neuronal deficits in AD models both in vitro and in vivo. As the first study to specifically determine the potential involvement of MICOS abnormalities in causing mitochondrial dysfunction and pathogenesis of AD, our proposal will likely pave the road for larger studies to shed new light on a novel mechanism underlying mitochondrial dysfunction in the pathogenesis of AD and provide innovative therapeutic targets for future drug development to fight against AD.