Endogenous but not sensory-driven activity controls migration, morphogenesis and survival of adult-born juxtaglomerular neurons in the mouse olfactory bulb

Cellular and Molecular Life Sciences (2023) 80:98 https://doi.org/10.1007/s00018-023-04753-4 Cellular and Molecular Life Sciences ORIGINAL ARTICLE Endogenous but not sensory‑driven activity controls migration, morphogenesis and survival of adult‑born juxtaglomerular neurons in the mouse olfactory bulb Kaizhen Li1,7 · Katherine Figarella1 · Xin Su1 · Yury Kovalchuk1 · Jessika Gorzolka1 · Jonas J. Neher2,3 · Nima Mojtahedi1 · Nicolas Casadei4,5 · Ulrike B. S. Hedrich6 · Olga Garaschuk1 Received: 25 August 2022 / Revised: 6 February 2023 / Accepted: 7 March 2023 © The Author(s) 2023 Abstract The development and survival of adult-born neurons are believed to be driven by sensory signaling. Here, in vivo analyses of motility, morphology and Ca2+ signaling, as well as transcriptome analyses of adult-born juxtaglomerular cells with reduced endogenous excitability (via cell-specific overexpression of either Kv1.2 or Kir2.1 K+ channels), revealed a pronounced impairment of migration, morphogenesis, survival, and functional integration of these cells into the mouse olfactory bulb, accompanied by a reduction in cytosolic Ca2+ fluctuations, phosphorylation of CREB and pCREB-mediated gene expression. Moreover, K+ channel overexpression strongly downregulated genes involved in neuronal migration, differentiation, and morphogenesis and upregulated apoptosis-related genes, thus locking adult-born cells in an immature and vulnerable state. Surprisingly, cells deprived of sensory-driven activity developed normally. Together, the data reveal signaling pathways connecting the endogenous intermittent neuronal activity/Ca2+ fluctuations as well as enhanced Kv1.2/Kir2.1 K+ channel function to migration, maturation, and survival of adult-born neurons. Keywords Adult neurogenesis · Potassium channels · Olfactory bulb · Neuronal development · Endogenous activity · Spontaneous calcium transients · pCREB · Migration · Differentiation · Survival Introduction Katherine Figarella and Xin Su contributed equally. * Olga Garaschuk 1 Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany 2 German Center for Neurodegenerative Diseases (DZNE), Tübingen, Germany 3 Department of Cellular Neurology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany 4 Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany 5 NGS Competence Center Tübingen, Tübingen, Germany 6 Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany 7 Present Address: Department of Physiology, University of Bern, Bern, Switzerland The rodent olfactory bulb (OB) is a highly plastic brain region receiving new neurons throughout life. Cumulative evidence revealed an important role of these cells for the fine-tuning of odor perception/discrimination, facilitation of task-dependent pattern separation, learning and memory [1–6]. Generated in the subventricular zone (SVZ) of the lateral ventricle [7, 8], adult-born cells migrate along the rostral migratory stream (RMS) into the OB and differentiate into local GABAergic interneurons: granule cells (GCs) and juxtaglomerular cells (JGCs) [9]. Many molecules including GABA, glutamate, dopamine, serotonin, BDNF, and cAMP response element-binding protein (CREB) influence adult OB neurogenesis [10–14]. Yet, the exact mechanisms underlying the migration, maturation, and incorporation of adultborn neurons into the existent OB circuitry remain unclear. Many studies point to the key role of sensory experience [15–18]. Indeed, adult-born cells respond to odorants right after their appearance in the OB [19, 20], develop larger and more complex dendritic trees in the odor-enriched environment 13 Vol.:(0123456789) 98 Page 2 of 20 [21], and manipulations increasing sensory-driven activity like odor enrichment [22, 23], odor discrimination training [5, 24] or olfactory learning [25] increased the survival and integration of adult-born cells. Conversely, manipulations reducing sensory-driven activity like naris occlusion [16, 26–28], naris cauterization and benzodiazepine treatment [29], knocking-out olfactory receptors in olfactory sensory neurons [30] or their axotomy [31] were reported to decrease survival and integration of adult-born neurons. Alternatively, the endogenous activity might be of great importance. An indirect support for this assumption comes from the fact that adult-born JGCs developing in sensorydeprived bulbs had normal dendritic morphology and dynamics [32] and the apoptosis of adult-born OB neurons was induced by the chemogenetic activation of higher-order odor-processing brain areas [33], synapsing on these cells. However, the strong and cell-specific reduction of the excitability of adult-born GCs via expression of a nonrectifying variant of the Kir2.1 K+ channel did not affect the initial stages of their development. The cells successfully migrated into the OB, survived there for 2 weeks and developed normal synaptic contacts and spines [34]. Yet, many of them died later, at 4 weeks of age. Using a similar approach in neonatally-born GCs confirmed that endogenous activity is not required for their tangential (in RMS) or radial (towards the OB surface) migration but is needed for normal positioning and survival of GCs [35]. Of note, the same experimental protocol did not impact the positioning or survival of JGCs, thus revealing a striking difference between the two cell populations. Moreover, while adult-born GCs migrate straight to their final destinations and integrate therein, adult-born JGCs (abJGCs) first enter the 3–4 weeks long pre-integration phase [36]. This phase, during which abJGCs undergo a millimeter-long lateral migration [36], extensively grow and prune their dendritic trees [19, 37] and exhibit ongoing endogenous activity [38] is unique to abJGCs and largely unexplored. Therefore, in the current study we have tested the role of the endogenous activity for migration, morphogenesis, and survival of abJGCs during the pre-integration phase. To do so, we genetically suppressed their excitability and used longitudinal in vivo two-photon imaging to monitor their developmental history. To understand the molecular pathways involved, we analyzed the transcriptome of adultborn cells right after their arrival into the OB. Materials and methods Mouse models Three- to four-month-old C57BL/6 mice of either sex were used in this study and were assigned randomly to control 13 K. Li et al. and test groups. Animals were kept in pathogen-free conditions at 22 °C, 60% air humidity, 12-h light–dark cycle with ad libitum access to food and water. Females stayed in groups of 3–5 mice, males were kept individually. Mice of similar age were assigned randomly to control and test groups. Littermates were evenly distributed among experimental groups and each experimental group containe (...truncated)