David M. Holtzman
David M. Holtzman is an American neurologist and neuroscientist known for his work exploring the biological mechanisms underlying neurodegeneration, with a focus on Alzheimer's Disease. Holtzman is Professor and former Chair of the Department of Neurology, Scientific Director of the Hope Center for Neurological Disorders, and associate director of the Knight Alzheimer's Disease Research Center at Washington University School of Medicine in St. Louis, Missouri. Holtzman's lab is known for uncovering how apoE4 contributes to Alzheimer's disease as well as how sleep modulates amyloid beta in the brain. His work has also examined  the contributions of microglia to AD pathology. Early life and education. Holtzman was born in St. Louis, Missouri. Holtzman pursued a six-year combined Bachelor's and Medical Degree at Northwestern University in Evanston, Illinois. He obtained his Bachelors of Science in Medical Education in 1983 and his Medical Degree in 1985. After completing his MD, Holtzman pursued a residency in Neurology at the University of California, San Francisco (UCSF) from 1985 to 1989. Following his residency, he completed his postdoctoral research under the mentorship of William C. Mobley at UCSF from 1989 to 1994. His postdoctoral research focused on  developing mouse models of neonatal stroke and neurodegeneration as well as elucidating the role neurotrophins play in modulating neuronal activity. Career and research. In 1994, Holtzman became an assistant professor at Washington University in St. Louis. By 2002, Holtzman was promoted to Associate Professor of Neurology, and by 2003, he was promoted to Full Professor in the Departments of Neurology and Developmental Biology at Washington University. In 2003, he also became the Chairman of the Department of Neurology, and in 2015 he became the Scientific Director of the Hope Center for Neurological Disorders. Holtzman is currently Professor of Neurology, scientific  director of the Hope Center for Neurological Disorders, and associate director of the Knight Alzheimer's Disease Research Center at Washington University School of Medicine. He stepped down from his position as department chairman in 2021.  The Holtzman Lab is dedicated to exploring the biological mechanisms underlying neurodegeneration. Holtzman's work has studied mechanisms by which apoE, amyloid beta, and tau metabolism are implicated in neurodegeneration in the context of Alzheimer's disease. Holtzman is also a co-founder of C2N Diagnostics, LLC. Holtzman and his former trainee, Randall Bateman, developed C2N Diagnostics in 2007 with the goal of increasing  the understanding the molecular mechanisms underlying neurological diseases through measurements of concentration and metabolism of CNS-derived biomolecules. Apolipoprotein E and Alzheimer's disease. Holtzman and his lab have examined the role of apoE in AD pathogenesis. Both the ε4 and ε2 APOE alleles increase the risk of developing AD, with an approximately 12-fold AD risk for those with two copies of ε4 allele. Holtzman's Lab has shown that apoE contributes to AD susceptibility and pathogenesis by its modulation of Aβ clearance and aggregation. Specifically, they have found that different isoforms of apoE have differential effects on soluble  Aβ clearance. When apoE binding proteins, such as LDLR, are up-regulated to decrease apoE, they found enhanced Aβ clearance and decreased Aβ depositions in the brains of mice. They also found that apoE is implicated in neurodegeneration through aberrant activation of the brain's innate immune cells, microglia. Immunotherapeutic approaches for Alzheimer's disease. The Holtzman Lab has shown the therapeutic benefits of antibody therapies in the context of AD. In 2001, Holtzman and his team published a paper showing that administration of the anti-Aβ antibody (m266) in mice changes the equilibrium of Aβ across the CNS and  blood plasma leading to increased Aβ sequestration in plasma which reduces the burden of Aβ in the brain. This antibody, m266, was licensed to Eli Lilly and humanized.  Using the humanized anti-Aβ antibody, Solanezumab, Eli Lilly began a series of clinical trials to discern the therapeutic potential of anti-Aβ immunotherapy in humans with AD. Results of these trials were disappointing. Solanezunmab treatment did not meet the primary endpoint of the clinical trials in mild AD, however, a clinical trial known as A4 in “presymptomatic” AD is still ongoing. Holtzman's lab has also focused on anti-tau immunotherapeutic  approaches to treating AD, and this approach is now in phase II clinical trials following licensing of an anti-tau antibody his lab developed with AbbVie. Amyloid and Synaptic Activity. Using novel tools, such as in vivo microdialysis in combination with electrophysiology, Holtzman and his team were able to discern that synaptic activity influences Aβ levels in the brain. They also found that Aβ deposition is brain region dependent, specifically correlating with regions involved in the default mode network. These findings suggest that increased metabolic demands and activity levels lead to higher soluble Aβ loads in these brain regions involved  in the default mode network. Sleep and Alzheimer’s Disease. The Holtzman lab has made important advances in our understanding of how sleep cycles influence Aβ concentrations in the brain interstitial fluid and Cerebrospinal Fluid. They found that Aβ and tau are higher during wakefulness and lower during sleep, and that these differences in Aβ and tau dynamics are driven by synaptic activity differences and orexin signaling. Following this work, Holtzman and his team found that once Aβ has been deposited, it results in sleep disruptions and further Aβ aggregation in a positive feedback loop promoting increased pathology. They also  found that sleep cycles are implicated in the release of extracellular tau and that less NREM sleep is linked to increased tau pathology.