Research

Overview

The lipid composition of neuronal membrane is crucial in regulating the ion gradients and the neurotransmission across membranes. During these events, the lipid composition changes so as to modulate the properties and the functions of the proteins embedded within the membrane. To facilitate these changes, key regulatory enzymes converge at cellular domains which act as functional platforms for the regulation of the cellular metabolism. One such regulatory platform consists of endoplasmic reticulum (ER)-membranes associated with mitochondria, or MAMs, which are responsible for communication between ER and mitochondria in regulating metabolic changes.

Alzheimer’s Disease

We have found that C99 is highly localized at MAMs. C99 is one of products of APP processed by beta-secretase and is downregulated by gamma-secretase, generating beta-amyloid. Our data indicates that elevated levels of C99 correlate with the dysregulation of cholesterol and sphingolipid regulation (Pera et al., 2017). We are currently researching how C99 contributes to the regulation of lipid homeostasis, and how the alteration in the level of C99 in MAMs plays a role in the pathogenesis of AD.

Representative electron micrographs of ER apposed to mitochondria (M) (i.e. MAM) in fibroblasts from a control subject, an FAD patient, and an SAD patient. Note the unusually large area of apposition in the FAD patient, extending for more than 1000 … — Representative electron micrographs of ER apposed to mitochondria (M) (i.e. MAM) in fibroblasts from a control subject, an FAD patient, and an SAD patient. Note the unusually large area of apposition in the FAD patient, extending for more than 1000 nm (arrowheads). (Area-Gomez et al., 2012)

Amyotrophic Lateral Sclerosis

Cells and animal models carrying ALS pathogenic mutations in superoxide dismutase 1 (SOD1) and FUS1 have shown significant alterations in MAM regulation in motor neurons. We are clarifying what aspects of MAM regulation are potentially affected in ALS and their influence on the early mitochondrial deficits seen in this disease. For that, using biochemical, molecular and imaging approaches, we are examining MAM dysregulation and its consequences in vivo using cultured motor neurons differentiated from human pluripotent stem cells derived from ALS patients and controls.

Parkinson’s Disease

We have recently shown that wild-type α-syn is not present in mitochondria as previously thought (Li et al., 2007: Cole et al., 2008: Devi et al., 2008: Parihar et al., 2008) but rather is in the MAM (Guardia-Laguarta et al., 2014). Remarkably, we found that PD-related mutated α-syn result in its reduced association with MAM, coincident with a lower degree of apposition of ER with mitochondria, and an increase in mitochondrial fragmentation, as compared to wild-type. This striking fragmentation phenotype could not be rescued by pharmacological or genetic interventions aimed at modulating the molecular machinery that controls mitochondrial shape and size, implying that α-syn operates downstream of it. However, overexpression of wild-type α-syn in mutant α-syn-expressing cells rescued the fragmented phenotype. These novel results indicate that wild-type α-syn localizes to the MAM and modulates mitochondrial morphology, and that these behaviors are impaired by pathogenic mutations in α-syn.

Example of colocalization of ER labeled with GFP-Sec61-Beta (green), and mitochondria labeled with pDsRed2-mito (red), in M17 dopaminergic cell expressing A30P- synculein mutation.

Traumatic Brain Injury

In collaboration with the labs of Dr. Richard Deckelbaum and Dr. Steven Kernie, our lab has recently begun studying traumatic brain injury (TBI) as an environmental cause of Alzheimer’s Disease (AD). The correlation between repeated brain injury and dementia later in life is well established, but the molecular mechanism that links the two diseases has not been determined. Our group has observed MAM functionality to be consistently altered in multiple cellular and animal models of AD (Area-Gomez et al., 2012). Of note, upregulated activity of MAM-resident enzymes occurs prior to the manifestation of canonical AD markers such as amyloid-β plaques and tau tangles. Given MAM’s role as a sensor of cellular lipid homeostasis and coordinator of cellular lipid metabolism, lipidomics analysis offers insight into MAM activity levels. Preliminary lipidomics studies in a mouse model of TBI point to an upregulation of MAM functions after brain injury. The goal of this project is to follow up on these studies and characterize MAM activity levels in TBI through biochemical activity assays and imaging-based approaches. We also have ongoing studies aiming to recapitulate alterations in APP metabolism observed in AD models. Eventually, we hope to determine whether genetic and environmental causes of AD converge on a mutual upregulation of MAM functions.