Effects of interferon-alpha on hippocampal neurogenesis and behavior in common marmosets

Exploring the origins of neurodevelopmental proteasomopathies associated with cardiac malformations: are neural crest cells central to certain pathological mechanisms?

Neurodevelopmental proteasomopathies constitute a recently defined class of rare Mendelian disorders, arising from genomic alterations in proteasome-related genes. These alterations result in the dysfunction of proteasomes, which are multi-subunit protein complexes essential for maintaining cellular protein homeostasis. The clinical phenotype of these diseases manifests as a syndromic association involving impaired neural development and multisystem abnormalities, notably craniofacial anomalies and malformations of the cardiac outflow tract (OFT). These observations suggest that proteasome loss-of-function variants primarily affect specific embryonic cell types which serve as origins for both craniofacial structures and the conotruncal portion of the heart. In this hypothesis article, we propose that neural crest cells (NCCs), a highly multipotent cell population, which generates craniofacial skeleton, mesenchyme as well as the OFT of the heart, in addition to many other derivatives, would exhibit a distinctive vulnerability to protein homeostasis perturbations. Herein, we introduce the diverse cellular compensatory pathways activated in response to protein homeostasis disruption and explore their potential implications for NCC physiology. Altogether, the paper advocates for investigating proteasome biology within NCCs and their early cranial and cardiac derivatives, offering a rationale for future exploration and laying the initial groundwork for therapeutic considerations.

Neurodevelopmental and Neuropsychiatric Disorders

This chapter will focus on microglial involvement in neurodevelopmental and neuropsychiatric disorders, particularly autism spectrum disorder (ASD), schizophrenia and major depressive disorder (MDD). We will describe the neuroimmune risk factors that contribute to the etiopathology of these disorders across the lifespan, including both in early life and adulthood. Microglia, being the resident immune cells of the central nervous system, could play a key role in triggering and determining the outcome of these disorders. This chapter will review preclinical and clinical findings where microglial morphology and function were examined in the contexts of ASD, schizophrenia and MDD. Clinical evidence points out to altered microglial morphology and reactivity, as well as increased expression of pro-inflammatory cytokines, supporting the idea that microglial abnormalities are involved in these disorders. Indeed, animal models for these disorders found altered microglial morphology and homeostatic functions which resulted in behaviours related to these disorders. Additionally, as microglia have emerged as promising therapeutic targets, we will also address in this chapter therapies involving microglial mechanisms for the treatment of neurodevelopmental and neuropsychiatric disorders.

Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models

Anhedonia, as evidenced by impaired pleasurable response to reward, reduced reward motivation, and/or deficits in reward-related learning, is a common feature of depression. Such deficits in reward processing are also an important clinical target as a risk factor for depression onset. Unfortunately, reward-related deficits remain difficult to treat. To address this gap and inform the development of effective prevention and treatment strategies, it is critical to understand the mechanisms that drive impairments in reward function. Stress-induced inflammation is a plausible mechanism of reward deficits. The purpose of this paper is to review evidence for two components of this psychobiological pathway: 1) the effects of stress on reward function; and 2) the effects of inflammation on reward function. Within these two areas, we draw upon preclinical and clinical models, distinguish between acute and chronic effects of stress and inflammation, and address specific domains of reward dysregulation. By addressing these contextual factors, the review reveals a nuanced literature which might be targeted for additional scientific inquiry to inform the development of precise interventions.

Maternal immune activation primes deficiencies in adult hippocampal neurogenesis

Neurogenesis, the process in which new neurons are generated, occurs throughout life in the mammalian hippocampus. Decreased adult hippocampal neurogenesis (AHN) is a common feature across psychiatric disorders, including schizophrenia, depression- and anxiety-related behaviours, and is highly regulated by environmental influences. Epidemiological studies have consistently implicated maternal immune activation (MIA) during neurodevelopment as a risk factor for psychiatric disorders in adulthood. The extent to which the reduction of hippocampal neurogenesis in adulthood may be driven by early life exposures, such as MIA, is however unclear. We therefore reviewed the literature for evidence of the involvement of MIA in disrupting AHN. Consistent with our hypothesis, data from both in vivo murine and in vitro human models of AHN provide evidence for key roles of specific cytokines induced by MIA in the foetal brain in disrupting hippocampal neural progenitor cell proliferation and differentiation early in development. The precise molecular mechanisms however remain unclear. Nonetheless, these data suggest a potential latent vulnerability mechanism, whereby MIA primes dysfunction in the unique hippocampal pool of neural stem/progenitor cells. This renders offspring potentially more susceptible to additional environmental exposures later in life, such as chronic stress, resulting in the unmasking of psychopathology. We highlight the need for studies to test this hypothesis using validated animal models of MIA, but also to test the relevance of such data for human pathology at a molecular basis through the use of patient-derived induced pluripotent stem cells (hiPSC) differentiated into hippocampal progenitor cells.