Faculty Bibliography

Background: Cystinuria is a disease of impaired absorption of cystine and dibasic amino acids (DAA) from the intestine and renal tubule leading to formation of cystine kidney stones. However, the metabolic impact of reduced amino acid absorption and excessive loss in the urine is poorly understood. We measured endogenous, gut microbial, and xenobiotic metabolites, providing insight into consequences of the disease and its treatment.
Method(s): Urinary biochemicals were assayed using LC-MS in 293 urine specimens from patients with cystinuria or control urinary phenotypes. Multivariate statistical analyses were conducted to reveal statistically significant biochemical signatures of the disease and products of cysteine-binding thiol drugs (CBTDs). 16s rRNA gene sequencing was performed on fecal samples from 12 wildtype (WT) and 12 cystinuric (Slc3a1 knockout; KO) mice to evaluate their gut microbial composition.
Result(s): Cystinuric urine samples had elevated levels of cysteine-gamma-glutamyl cystine disulfide (glutathione precursor), indole-3-acetic acid (microbial tryptophan metabolism), and novel conjugated forms of putrescine (microbial DAA decomposition). Conversely, taurine (sulfur metabolism), indole-3-acetic acid-glucuronide, and novel urinary metabolite N-methyl pipecolic acid (lysine metabolism) were reduced in cystinuric urine. Where cysteine-bound CBTDs were observed, substantial amounts of "wasted" drug were also detected as CBTD homodimers, non-cysteine disulfides, and mixed drug disulfides. The differentiation of gut microbially-derived metabolites led us to evaluate the gut microbiome diversity and composition in a mouse model of cystinuria revealing clear beta diversity and taxa differentiation between WT and KO mice.
Conclusion(s): Cystinuria is associated with unique urinary metabolic profiles beyond hyperexcretion of cystine and DAA, indicating perturbed metabolic processes and potential gut microbial effects. Study of the gut microbiome of WT and KO mice provides the first evidence for them having distinct taxa, perhaps due to poorly absorbed DAA present in the intestinal lumen. Urinary profiles allow us to characterize the excretion profiles of CBTDs, providing insight which may be helpful to tailor treatment

Objective: To describe an unusual case of a young girl of Jewish Ashkenazi descent with two rare genetic disorders: familial dysautonomia and congenital adrenal hyperplasia.
Method(s): Case report.
Result(s): Female patient presenting with hypotonia, failure to thrive, recurrent vomiting and frequent lower respiratory tract infections during the first year of life. Her physical exam disclosed genital ambiguity and, because an older sister had a diagnosis of congenital adrenal hyperplasia, the diagnosis was suspected in this case, and confirmed by low levels of cortisol and aldosterone. Targeted genetic testing showed homozygosis for a pathogenic variant in the CYP21A2 gene (c.293-13C[G, aka I2G, well-described in Jewish Ashkenazi patients) and heterozygosis for 7 other variants in the same gene. She was started on fludrocortisone for mineralocorticoid replacement therapy. Additional signs and symptoms were identified including frequent aspiration pneumonias prompting a gastrostomy tube placement at 6 months of age, emotionally-induced episodes of face, hand and feet blotching, frequent falls, impaired sensitivity to pain, and lack of tears. Additional genetic testing at age 2 disclosed homozygous copies of the founder mutation variant of familial dysautonomia (variant IVS20?6 T[C) in the IKBKAP gene.
Conclusion(s): The presence of one rare genetic disorder does not preclude the presence of another rare genetic disorder. Signs and symptoms not consistent with one diagnosed genetic disorder should prompt suspicion of additional causes

Different strategies for treatment and prevention of Alzheimer's disease (AD) are currently under investigation, including passive immunization with anti-amyloid β (anti-Aβ) monoclonal antibodies (mAbs). Here, we investigate the therapeutic potential of a novel type of Aβ-targeting agent based on an affibody molecule with fundamentally different properties to mAbs. We generated a therapeutic candidate, denoted Z_SYM73-albumin-binding domain (ABD; 16.8 kDa), by genetic linkage of the dimeric Z_SYM73 affibody for sequestering of monomeric Aβ-peptides and an ABD for extension of its in vivo half-life. Amyloid precursor protein (APP)/PS1 transgenic AD mice were administered with Z_SYM73-ABD, followed by behavioral examination and immunohistochemistry. Results demonstrated rescued cognitive functions and significantly lower amyloid burden in the treated animals compared to controls. No toxicological symptoms or immunology-related side-effects were observed. To our knowledge, this is the first reported in vivo investigation of a systemically delivered scaffold protein against monomeric Aβ, demonstrating a therapeutic potential for prevention of AD.

Motion selectivity in primary visual cortex (V1) is approximately separable in orientation, spatial frequency, and temporal frequency ("frequency-separable"). Models for area MT neurons posit that their selectivity arises by combining direction-selective V1 afferents whose tuning is organized around a tilted plane in the frequency domain, specifying a particular direction and speed ("velocity-separable"). This construction explains "pattern direction selective" MT neurons, which are velocity-selective but relatively invariant to spatial structure, including spatial frequency, texture and shape. We designed a set of experiments to distinguish frequency- and velocity-separable models and executed them with single-unit recordings in macaque V1 and MT. Surprisingly, when tested with single drifting gratings, most MT neurons' responses are fit equally well by models with either form of separability. However, responses to plaids (sums of two moving gratings) tend to be better described as velocity-separable, especially for pattern neurons. We conclude that direction selectivity in MT is primarily computed by summing V1 afferents, but pattern-invariant velocity tuning for complex stimuli may arise from local, recurrent interactions.Significance Statement How do sensory systems build representations of complex features from simpler ones? Visual motion representation in cortex is a well-studied example: the direction and speed of moving objects, regardless of shape or texture, is computed from the local motion of oriented edges. Here we quantify tuning properties based on single-unit recordings in primate area MT, then fit a novel, generalized model of motion computation. The model reveals two core properties of MT neurons - speed tuning and invariance to local edge orientation - result from a single organizing principle: each MT neuron combines afferents that represent edge motions consistent with a common velocity, much as V1 simple cells combine thalamic inputs consistent with a common orientation.

Many brain functions frequently change across a life span in response to new experience, the rewiring of neural circuits, homeostatic factors, and environmental events. Extracellular signals can promote rapid responses in gene expression and protein synthesis that trigger growth and plasticity in the nervous system. A key component is activity-dependent events and their participation in synaptic function. These responses are required for long-lasting effects in synaptic plasticity associated with learning and memory. The neurotrophin brain-derived neurotrophic factor (BDNF), discovered in 1982, is well established as a prominent molecule responsible for inducing synaptogenesis, dendritic growth, and long-term potentiation. This volume of the Neuromethods Series is dedicated to the methods that have allowed to study the many potential mechanisms whereby BDNF signaling accounts for its many physiological effects.
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