Probes for INS

Chronic inflammation is frequently invoked as a mechanism of neurodegeneration and yet inflammatory cell infiltrates are seldom seen in brains of these disorders. Different disciplines utilize different technologies and methodologies to describe what is immunologically defined as the innate immune response (IIR). We examined murine models of the human neurodegenerative disease Aicardi-Goutières Syndrome, where an IIR is initiated by aberrant RNA metabolism secondary to a mutation in adenosine deaminase acting on RNA gene (ADAR1). We previously showed that these mice demonstrated a deficit in RNA editing that lead to MDA-5 mediated RNA sensing pathway activation of the IIR with massive interferon stimulated gene transcription and translation. As early as 2 weeks of age, in situ hybridization demonstrated that different central nervous system (CNS) cell lineages expressed very high levels of distinct interferon stimulated genes (ISGs) in the absence of interferon and absence of immune cell infiltrates. We have expanded these studies to more completely describe the breadth of ISG expression systemically and in CNS using double label in situ hybridization. Within the CNS aberrant ISG expression was mostly limited to neurons, microglia, ependyma, choroid plexus, and endothelial cells with little expression in oligodendroglia and astrocytes except for STAT1. Wild type controls showed a similar pattern of ISG expression but only in aged mice and at levels minimally detectable by in situ hybridization. Despite months of elevated ISG expression in mutant mice, there was essentially no inflammatory infiltrate, no interferon production and minimal glial reaction. Histomorphological neurodegenerative pathology of ventricular dilatation and deep gray matter mineralization were evident in mutant mice 8-13 months of age but this did not show a spatial relationship to ISG expression. This IIR without immune cell infiltration leads to neurodegeneration through non-canonical pathways that may accentuate normal aging pathways.

The brain plays a crucial role in maintaining the bodys energy needs, a process involving the activity of a group of hypothalamic neurons that express the neuropeptidergic marker pro-opiomelanocortin (POMC). POMC neuronal dysfunction can cause obesity and its associated metabolic sequelae. However, this population of neurons is highly diverse at a molecular and functional level, and whether or not such heterogeneity is implicated in disease establishment or progression has yet to be elucidated. Here, using a lineage-tracing approach in combination with histological and electrophysiological tools, we have characterized POMC neuronal cells at a single-cell resolution in control of lean and diet-induced obese (DIO) mice. Thanks to this genetic strategy, we traced with a reporter protein POMC neurons in adult mice, thus studying these neuronal cells independently from the expression of their main marker POMC. Different histological techniques, including immunohistochemistry, fluorescent in-situ hybridization, and RNAscope, have been used to cluster genetically traced POMC neuronal cells based on their expression of the main marker POMC. These different approaches consistently allowed the identification of a previously uncharacterized sub-population that expresses negligible POMC mRNA and protein levels, which we named Ghost-POMC neurons. We also observed that Ghost-POMC neurons are insensitive to acute nutritional cues (fasting and refeeding) relative to classic POMC positive neurons. Intriguingly, DIO mice presented an increased number of Ghost-POMC neurons relative to control animals. Furthermore, we developed an approach that combines whole-cell patch-clamp of traced POMC neurons with the subsequent molecular profiling of the patched cell by single-cell qPCR. Thanks to this approach, we observed that DIO leads to electrical alterations only in a fraction of POMC neurons expressing undetectable levels of POMC mRNA, which is reminiscent of the Ghost population previously identified by histological techniques. Thus, Ghost-POMC neurons might constitute a novel subpopulation of POMC neurons that undergo dysfunction in response to prolonged dietary cues, perhaps contributing to obesity establishment or progression.

Pleasant touch provides emotional and psychological support that helps mitigate social isolation and stress. However, the underlying mechanisms remain poorly understood. Using a pleasant touch-conditioned place preference (PT-CPP) test, we show that genetic ablation of spinal excitatory interneurons expressing prokineticin receptor 2 (PROKR2), or its ligand PROK2 in sensory neurons, abolishes PT-CPP without impairing pain and itch behaviors in mice. Mutant mice display profound impairments in stress response and prosocial behaviors. Moreover, PROKR2 neurons respond most vigorously to gentle stroking and encode reward value. Collectively, we identify PROK2 as a long-sought neuropeptide that encodes and transmits pleasant touch to spinal PROKR2 neurons. These findings may have important implications for elucidating mechanisms by which pleasant touch deprivation contributes to social avoidance behavior and mental disorders.

In mammals, chemoperception relies on a diverse set of neuronal sensors able to detect chemicals present in the environment, and to adapt to various levels of stimulation. The contribution of endogenous and external factors to these neuronal identities remains to be determined. Taking advantage of the parallel coding lines present in the olfactory system, we explored the potential variations of neuronal identities before and after olfactory experience. We found that at rest, the transcriptomic profiles of mouse olfactory sensory neuron populations are already divergent, specific to the olfactory receptor they express, and are associated with the sequence of these latter. These divergent profiles further evolve in response to the environment, as odorant exposure leads to reprogramming via the modulation of transcription. These findings highlight a broad range of sensory neuron identities that are present at rest and that adapt to the experience of the individual, thus adding to the complexity and flexibility of sensory coding.