Why is there a higher incidence of AD in Black Populations, could Reelin be the key to a cure?
Five years ago, the Lieber Institute for Brain Development at Johns Hopkins University partnered with Morgan State University and the Black community of Baltimore to enhance the representation of African ancestry in genomic and neuroscience research. Recently, the inaugural paper from this partnership, the African Ancestry Neuroscience Research Initiative, was featured in Nature Neuroscience. It revealed that African ancestry correlates with a higher incidence of certain neurological conditions like Alzheimer's disease, but not with behavioral disorders like depression.
Contradicting some expectations, Black participants in Alzheimer's disease (AD) research studies were found to be 35% less likely to receive a diagnosis of Alzheimer's and related dementias compared to white participants. This is despite national statistics claiming that Black Americans are about twice as likely to develop these dementias as whites. Data analysis from the National Institute on Aging's Alzheimer's Disease Research Centers network also revealed that Black participants diagnosed with Alzheimer's and related dementias according to majority white doctors exhibited more risk factors, greater cognitive impairment, and more severe symptoms than their white counterparts. These findings were published in the journal Alzheimer's and Dementia.
New research has shown that the disparity is most likely caused by diet. Clinical results show that the western diet pattern is a risk factor for developing AD. In contrast, the Mediterranean diet, ketogenic diet, and supplementation with omega-3 fatty acids and probiotics are highly protective factors. But the most promising results have been seen by combining good diet with the supplement CoQ10. Coenzyme Q10 (CoQ10), a lipophilic substituted benzoquinone, is present in animal and plant cells. It is endogenously synthetized in every cell and involved in a variety of cellular processes.
CoQ10 is an essential component of the respiratory chain located within the inner mitochondrial membrane. It is also found in all cellular membranes and the bloodstream. As the only endogenous lipid antioxidant, CoQ10 serves as a fundamental building block for cells. It plays a critical role in uncoupling proteins and in regulating the mitochondrial permeability transition pore. Additionally, CoQ10 is involved in maintaining and regulating the physicochemical properties of membranes. Its effect on gene expression can influence overall metabolism. Changes in the tissue by enhancing concentration of CoQ10 during aging and under various pathophysiological conditions can positively impact cellular functions.
Primary changes in the energetic and antioxidant functions can explain its remedial effects. CoQ10 supplementation is safe and well-tolerated, even at high doses. CoQ10 does not cause any serious adverse effects in humans. CoQ10 supplementations are recommended in some neurological diseases such as migraine, Parkinson´s disease, Huntington´s disease, Alzheimer´s disease, amyotrophic lateral sclerosis, Friedreich´s ataxia or multiple sclerosis. Cardiovascular hypertension was included because of its central mechanisms controlling blood pressure in the brainstem rostral ventrolateral medulla and hypothalamic paraventricular nucleus. In conclusion, it seems reasonable to recommend CoQ10 as adjunct to conventional therapy in many cases especially as a preventative measure.
Decades of research have conclusively shown that genetic variation can affect cognitive function measures. However, the conclusions some have drawn about the implications of these findings for racial differences in cognitive ability are highly questionable. There is no strong scientific justification for prioritizing and investing significant resources in investigating average disparities in intelligence or other cognitive abilities among groups with unclear and ever-changing boundaries that cannot be definitively determined.
The loss of pigmented neurons from the human brain has long been the hallmark of Parkinson's disease (PD). Neuromelanin (NM) in the pre-synaptic terminal of dopamine neurons is emerging as a primary player in the etiology of neurodegenerative disorders including PD. A study of 48 post-mortem brains found a protein that appears to protect brain cells from Alzheimer's — even in people who had significant amounts of amyloid plaques in their brains. The protein is called reelin. A Colombian man who should have developed Alzheimer's in middle age but didn't was part of a large family in the area around Medellin that carries a very rare gene variant. Dr. Joseph Arboleda-Velasquez of Harvard Medical School says family members who inherit the gene are virtually certain to develop Alzheimer's.
Individuals carrying a certain gene typically begin to experience cognitive decline in their 40s, which can progress to full-blown dementia by their late 40s or early 50s. However, one man in his late 60s remained cognitively intact. Posthumously, scientists discovered his brain was filled with amyloid plaques, indicative of Alzheimer's disease. They also identified another Alzheimer's marker, tau tangles. Intriguingly, Arboleda-Velasquez noted that these tangles were largely absent from the entorhinal cortex. The entorhinal cortex is part of the brain's allocortex, situated in the medial temporal lobe, and is crucial for memory, navigation, and time perception.
Future research will concentrate on brain regions containing the substantia nigra (SN), locus coeruleus (LC), amygdala, hippocampus, and entorhinal cortex. Neuromelanin has the ability to reversibly bind and interact with neurotoxins containing amines, such as MPTP, enhancing their effects in the terminal and ultimately causing instability and degeneration of melanin-containing neurons due to oxidative stress and mitochondrial dysfunction. Notably, neuromelanin seems to increase susceptibility to chemical toxicity by providing a substantial reservoir of iron-bound, heme-like structures within a pi-conjugated system, which is designed for stabilizing interactions, including pi-stacking and ligand binding to iron. Considering the age-related increase in neuromelanin alongside a decrease in dopamine synthesis, it is pertinent to question whether neuromelanin can also bind dopamine, the primary functional monoamine in these neurons. Reelin, known as a critical neuron guidance molecule for brain development, is the next focus to understand its protective role against these diseases.
Throughout embryonic development and into adulthood, Reelin plays a crucial role in the brain by overseeing various key functions such as regulating neuronal migration, dendritic growth, dendritic spine formation, synaptogenesis, and synaptic plasticity. Currently, researchers are exploring the presence of Reelin in melanocytes. At the cellular level, Reelin triggers the clustering of apolipoprotein E receptor 2 (ApoER2) and very-low-density lipoprotein receptor (VLDLR). It is also implicated in synaptic plasticity and the modulation of higher brain functions. Consequently, a deficiency in Reelin signaling may be linked to the development of neuropsychiatric disorders like epilepsy, schizophrenia, and autism. Recent findings have also suggested that reduced Reelin signaling could exacerbate Alzheimer’s disease (AD).
Reelin is produced by lymphatic endothelial cells and appears pertinent for lymphatic system development. Reelin has not only been observed in lymphatic endothelial cells, but also in human umbilical vein endothelial cells, and human microvascular endothelial cells. Reelin may also mediate cell migration to sites of brain injury (Courtès et al. 2011; Massalini et al. 2009). Preliminary evidence supports that Reelin, in addition to regulating cell migration during development, may have a role in regulating cell migration in response to brain injury.
Recently identified ADAMTS-3 lowers levels of reelin (a disintegrin and metalloproteinase with thrombospondin motifs 3) it is the major protease that mediates N-t cleavage in the embryonic and early postnatal cerebral cortex and hippocampus. More importantly, the results from ADAMTS-3 indicated that N-t cleavage is the primary mechanism of Reelin inactivation in these tissues. However, ADAMTS-3 was not the only protease to inactivate Reelin; its cleavage still occurred in the cerebral cortex and hippocampus of ADAMTS-3 KO subjects. The neuronal dendrites contained more branches and were elongated in the cerebral cortex of ADAMTS-3 conditional subjects. ADAMTS is a family of zinc metalloproteases with a characteristic domain structure: a signal sequence, a propeptide sequence, a metalloprotease (M)-domain with zinc-binding.
Accumulating evidence has uncovered a crucial role for the matrix metalloproteinase (MMP) and adamalysin families of proteases in immune responses. MMP and disintegrin metalloproteinase (ADAM) expression is tightly regulated in immune and stromal cells during inflammation. Active metalloproteinases modify immune substrates or cleave transmembrane receptors, thereby affecting cell–cell communication and intracellular signalling.
Importantly, Fatemi et al. (2005b) found that Reelin deficits were not restricted to individuals with psychosis, but extended to non-psychotic subjects with bipolar disorder as well (Fatemi et al. 2000, 2005b). The observed reduction in Reelin expression may account for the multiple brain abnormalities associated schizophrenia. Less is known regarding other members of the Reelin signaling pathway.
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