Why tracing cyclosporiasis is so tough, and a digestible probe for the microbiome
Science journalists discuss why the food-borne illness cyclosporiasis is difficult to track and a new map of a major highway in the human nervous system. Leslie Chan then explains an ingestible metabolic probe that detects gut-microbiome enzyme activity from volatile signals in the breath.
Western diet consumption and memory impairment: what, when, and how?
Habitual consumption of a “Western diet”, containing higher than recommended levels of simple sugars and saturated fatty acids, is associated with cognitive impairments in humans and in various experimental animal models. Emerging findings reveal that the specific mnemonic processes that are disrupted by Western diet consumption are those that rely on the hippocampus, a brain region classically linked with memory control and more recently with the higher-order control of food intake. Our laboratory has established rat models in which excessive consumption of different components of a Western diet during the juvenile and adolescent periods of development yields long-term impairments in hippocampal-dependent memory function without concomitant increases in total caloric intake, body weight, or adiposity. Our ongoing work is investigating alterations in the gut microbiome as a potential underlying neurobiological mechanism linking early life unhealthy dietary factors to adverse neurocognitive outcomes.
Gestational exposure to environmental toxins, infections, and stressors are epidemiologically linked to neurodevelopmental disorders
Gestational exposure to environmental toxins, infections, and stressors are epidemiologically linked to neurodevelopmental disorders with strong male-bias, such as autism spectrum disorder. We modeled some of these prenatal risk factors in mice, by co-exposing pregnant dams to an environmental pollutant and limited-resource stress, which robustly dysregulated the maternal immune system. Male but not female offspring displayed long-lasting behavioral abnormalities and alterations in the activity of brain networks encoding social interactions, along with disruptions of gut structure and microbiome composition. Cellularly, prenatal stressors impaired microglial synaptic pruning in males during early postnatal development. Precise inhibition of microglial phagocytosis during the same critical period mimicked the impact of prenatal stressors on the male-specific social deficits. Conversely, modifying the gut microbiome rescued the social and cellular deficits, indicating that environmental stressors alter neural circuit formation in males via impairing microglia function during development, perhaps via a gut-brain disruption.
New Strategies and Approaches to Tackle and Understand Neurological Disorder
Broadly, the Mauro Costa-Mattioli laboratory (The MCM Lab) encompasses two complementary lines of research. The first one, more traditional but very important, aims at unraveling the molecular mechanisms underlying memory formation (e.g., using state-of-the-art molecular and cell-specific genetic approaches). Learning and memory disorders can strike the brain during development (e.g., Autism Spectrum Disorders and Down Syndrome), as well as during adulthood (e.g., Alzheimer’s disease). We are interested in understanding the specific circuits and molecular pathways that are primarily targeted in these disorders and how they can be restored. To tackle these questions, we use a multidisciplinary, convergent and cross-species approach that combines mouse and fly genetics, molecular biology, electrophysiology, stem cell biology, optogenetics and behavioral techniques. The second line of research, more recent and relatively unexplored, is focused on understanding how gut microbes control CNS driven-behavior and brain function. Our recent discoveries, that microbes in the gut could modulate brain function and behavior in a very powerful way, have added a whole new dimension to the classic view of how complex behaviors are controlled. The unexpected findings have opened new avenues of study for us and are currently driving my lab to answer a host of new and very interesting questions: - What are the gut microbes (and metabolites) that regulate CNS-driven behaviors? Would it be possible to develop an unbiased screening method to identify specific microbes that regulate different behaviors? - If this is the case, can we identify how members of the gut microbiome (and their metabolites) mechanistically influence brain function? - What is the communication channel between the gut microbiota and the brain? Do different gut microbes use different ways to interact with the brain? - Could disruption of the gut microbial ecology cause neurodevelopmental dysfunction? If so, what is the impact of disruption in young and adult animals? - More importantly, could specific restoration of selected bacterial strains (new generation probiotics) represent a novel therapeutic approach for the targeted treatment of neurodevelopmental disorders? - Finally, can we develop microbiota-directed therapeutic foods to repair brain dysfunction in a variety of neurological disorders?
Interactions between the microbiome and nervous system during early development
The gut microbiota is emerging as an important modulator of brain function and behavior, as several recent discoveries reveal substantial effects of the microbiome on neurophysiology, neuroimmunity and animal behavior. Despite these findings supporting a “microbiome-gut-brain axis”, the molecular and cellular mechanisms that underlie interactions between the gut microbiota and brain remain poorly understood. To uncover these, the Hsiao laboratory is mining the human microbiota for microbial modulators of host neuroactive molecules, investigating the impact of microbiota-immune system interactions on neurodevelopment and examining the microbiome as an interface between gene-environment interactions in neurological diseases. In particular, our research on effects of the maternal microbiome on offspring development in utero are revealing novel interactions between microbiome-dependent metabolites and fetal thalamocortical axonogenesis. Overall, we aim to dissect biological pathways for communication between the gut microbiota and nervous system, toward understanding fundamental interactions between physiological systems that impact brain and behavior.
Modulation of C. elegans behavior by gut microbes
We are interested in understanding how microbes impact the behavior of host animals. Animal nervous systems likely evolved in environments richly surrounded by microbes, yet the impact of bacteria on nervous system function has been relatively under-studied. A challenge has been to identify systems in which both host and microbe are amenable to genetic manipulation, and which enable high-throughput behavioral screening in response to defined and naturalistic conditions. To accomplish these goals, we use an animal host — the roundworm C. elegans, which feeds on bacteria — in combination with its natural gut microbiome to identify inter-organismal signals driving host-microbe interactions and decision-making. C. elegans has some of the most extensive molecular, neurobiological and genetic tools of any multicellular eukaryote, and, coupled with the ease of gnotobiotic culture in these worms, represents a highly attractive system in which to study microbial influence on host behavior. Using this system, we discovered that commensal bacterial metabolites directly modulate nervous system function of their host. Beneficial gut microbes of the genus Providencia produce the neuromodulator tyramine in the C. elegans intestine. Using a combination of behavioral analysis, neurogenetics, metabolomics and bacterial genetics we established that bacterially produced tyramine is converted to octopamine in C. elegans, which acts directly in sensory neurons to reduce odor aversion and increase sensory preference for Providencia. We think that this type of sensory modulation may increase association of C. elegans with these microbes, increasing availability of this nutrient-rich food source for the worm and its progeny, while facilitating dispersal of the bacteria.