Biology subjects

Kalinski, A. L.

Publications and source records attributed to Kalinski, A. L..

6 recordsLinked to original sources

bioRxiv2026

SARM1 is required for macrophage immunophenotype switching that is essential for nerve repair

SARM1 is a key executor of Wallerian degeneration in axons. Global knockout of sarm1 in mice delays degeneration for several weeks. Recently, we reported that Schwann cell reprogramming, inflammation, and axon regeneration are also delayed in these animals. Several studies have also indicated that SARM1 has essential regulatory functions in macrophages (M{phi}). However, the role of SARM1 in M{phi} in the context of peripheral nerve injury remains unknown. Here, we report that loss of sarm1 impairs splenic M{phi} from adopting immunological stimuli driven immunophenotypes in culture. Through a combination of cell culture, Western blotting, gene expression analysis, in vivo injection of M{phi} into sciatic nerves, and generation of cell specific sarm1 conditional knockout mouse lines, we found that SARM1 is required for proper immunophenotypes in M{phi}. Loss of sarm1 in macrophages increases neurite length of sensory neurons in culture but delays regeneration in a model of peripheral nerve injury. We identified dysregulation of several inflammatory and anti-inflammatory immunological stimuli pathways and altered regulation of both iNOS and Arginase-1 in Sarm1-/- M{phi}. In culture, Sarm1-/- M{phi} display difficulty phagocytosing and clearing myelin debris and this was recapitulated in vivo with a M{phi} specific sarm1 knockout line. Generation of M{phi} and neuronal sarm1 conditional knockout mice further indicated that SARM1 is required in both cell types for an efficient response to peripheral nerve injury. This study provides the first evidence that SARM1 signaling in M{phi} is required for injury induced inflammation, degeneration, and axon regeneration.

neuroscience↗

bioRxiv2025

An axon-intrinsic loop restricts nerve regeneration through axonal protein synthesis

Injured axons synthesize the RNA Binding Protein KHSRP that promotes mRNA decay and slows nerve regeneration. Axotomy-induced increase in axoplasmic Ca2+ activates axonal Khsrp translation, and while Ca2+ returns to pre-injury levels within 16 hours post-axotomy, axonal KHSRP remains elevated. Alternating translation of Reg3a and Khsrp sustains axonal KHSRP levels in regenerating axons. Nerve injury activates Reg3a expression, resulting in increased REG3A synthesis and secretion from axons. REG3A stimulates ER Ca2+ release to activate PERK, increase eIF2 phosphorylation, and increase Khsrp translation. Axoplasmic Ca2+ slowly oscillates in growth cones and Reg3A depletion attenuates growth cone Ca2+ oscillations, decreases KHSRP synthesis, reduces the axons retractive events, and accelerates peripheral nerve regeneration. Thus, REG3A to KHSRP signaling provides an axon-intrinsic loop that decelerates axon growth through localized mRNA translation.

neuroscience↗

bioRxiv2025

LIS1 is critical for axon integrity in adult mice

Mutations in human LIS1 cause lissencephaly, a severe developmental brain malformation. Although most studies focus on development, LIS1 is also expressed in adult mouse tissues. We previously induced LIS1 knockout (iKO) in adult mice using a Cre-Lox approach with an actin promoter driving CreERT2 expression. This proved to be rapidly lethal, with evidence pointing toward nervous system dysfunction. CreERT2 activity was observed in astrocytes, brainstem and spinal motor neurons, and axons and Schwann cells in the sciatic and phrenic nerves, suggesting dysfunctional cardiorespiratory and motor circuits. However, it is unclear how LIS1 knockout in these different cell types contributes to the lethal phenotype. We now report that LIS1 depletion from astrocytes is not lethal to mice (male or female), although glial fibrillary protein (GFAP) expression is increased in all LIS1-depleted astrocytes. In contrast, LIS1 depletion from projection neurons causes motor deficits and rapid lethality in both males and females. This is accompanied by progressive, widespread axonal degeneration along the entire length of both motor and sensory axons. Interestingly, sensory neurons harvested from iKO mice initially extend axons in culture but soon develop axonal swellings and fragmentation, indicating axonal degeneration. LIS1 is a prominent regulator of cytoplasmic dynein 1 (dynein, hereafter), a microtubule motor whose disruption can cause both cortical malformations and later-onset neurodegenerative diseases, such as Charcot-Marie-Tooth disease. Our results raise the possibility that LIS1 depletion, through disruption of dynein function in mature axons, may lead to Wallerian-like axon degeneration without traumatic nerve injury. Significance StatementA healthy nervous system requires that proper brain wiring is maintained throughout the life of the animal. Connectivity often involves the long axons of projection neurons. Some axons drive cognition, others contribute to sensory and motor systems, while still others subserve vitally important cardiorespiratory processes. We show that LIS1, a protein linked to congenital brain abnormalities, also plays a crucial role in fully developed projection neurons in the adult mouse. LIS1 depletion from these cells causes severe axonal degeneration resembling the Wallerian degeneration that occurs in response to nerve injury. Because LIS1 regulates dynein, and because defective dynein can cause neurodegenerative disorders in humans, our study suggests that drugs targeting Wallerian degeneration may have therapeutic potential for dynein-related diseases.

neuroscience↗

bioRxiv2024

Sarm1 is not necessary for activation of neuron-intrinsic growth programs yet required for the Schwann cell repair response and peripheral nerve regeneration.

Upon peripheral nervous system (PNS) injury, severed axons undergo rapid SARM1-dependent Wallerian degeneration (WD). In mammals, the role of SARM1 in PNS regeneration, however, is unknown. Here we demonstrate that Sarm1 is not required for axotomy induced activation of neuron-intrinsic growth programs and axonal growth into a nerve crush site. However, in the distal nerve, Sarm1 is necessary for the timely induction of the Schwann cell (SC) repair response, nerve inflammation, myelin clearance, and regeneration of sensory and motor axons. In Sarm1-/- mice, regenerated fibers exhibit reduced axon caliber, defective nerve conduction, and recovery of motor function is delayed. The growth hostile environment of Sarm1-/- distal nerve tissue was demonstrated by grafting of Sarm1-/- nerve into WT recipients. SC lineage tracing in injured WT and Sarm1-/- mice revealed morphological differences. In the Sarm1-/- distal nerve, the appearance of p75NTR+, c-Jun+ SCs is significantly delayed. Ex vivo, p75NTR and c-Jun upregulation in Sarm1-/- nerves can be rescued by pharmacological inhibition of ErbB kinase. Together, our studies show that Sarm1 is not necessary for the activation of neuron intrinsic growth programs but in the distal nerve is required for the orchestration of cellular programs that underlie rapid axon extension.

neuroscience↗

bioRxiv2022

The Injured Sciatic Nerve Atlas (iSNAT), Insights into the Cellular and Molecular Basis of Neural Tissue Degeneration and Regeneration

Upon trauma, the adult murine PNS displays a remarkable degree of spontaneous anatomical and functional regeneration. To explore extrinsic mechanisms of neural repair, we carried out single cell analysis of naive mouse sciatic nerve, peripheral blood mononuclear cells, and crushed sciatic nerves at 1-day, 3-days, and 7-days following injury. During the first week, monocytes and macrophages (Mo/Mac) rapidly accumulate in the injured nerve and undergo extensive metabolic reprogramming. Proinflammatory Mo/Mac in the injured nerve show high glycolytic flux compared to Mo/Mac in blood and dominate the early injury response. They subsequently give way to inflammation resolving Mac, programmed toward oxidative phosphorylation. Nerve crush injury causes partial leakiness of the blood-nerve-barrier, proliferation of endoneurial and perineurial stromal cells, and accumulation of select serum proteins. Micro-dissection of the nerve injury site and distal nerve, followed by single-cell RNA-sequencing, identified distinct immune compartments, triggered by mechanical nerve wounding and Wallerian degeneration, respectively. This finding was independently confirmed with Sarm1-/- mice, where Wallerian degeneration is greatly delayed. Experiments with chimeric mice showed that wildtype immune cells readily enter the injury site in Sarm1-/- mice, but are sparse in the distal nerve, except for Mo. We used CellChat to explore intercellular communications in the naive and injured PNS and report on hundreds of ligand-receptor interactions. Our longitudinal analysis represents a new resource for nerve regeneration, reveals location specific immune microenvironments, and reports on large intercellular communication networks. To facilitate mining of scRNAseq datasets, we generated the injured sciatic nerve atlas (iSNAT): https://cdb-rshiny.med.umich.edu/Giger_iSNAT/

neuroscience↗

bioRxiv2020

Analysis of the Immune Response to Sciatic Nerve Injury Identifies Efferocytosis as a Key Mechanism of Nerve Debridement

Sciatic nerve crush injury triggers sterile inflammation within the distal nerve and axotomized dorsal root ganglia (DRGs). Granulocytes and pro-inflammatory Ly6Chigh monocytes infiltrate the nerve first, and rapidly give way to Ly6Cnegative inflammation-resolving macrophages. In axotomized DRGs, few hematogenous leukocytes are detected and resident macrophages acquire a ramified morphology. Single-cell RNA-sequencing of injured sciatic nerve identifies five macrophage subpopulations, repair Schwann cells, and mesenchymal precursor cells. Macrophages at the nerve crush site are molecularly distinct from macrophages associated with Wallerian degeneration. In the injured nerve, macrophages "eat" apoptotic leukocytes, a process called efferocytosis, and thereby promote an anti-inflammatory milieu. Myeloid cells in the injured nerve, but not axotomized DRGs, strongly express receptors for the cytokine GM-CSF. In GM-CSF deficient (Csf2-/-) mice, inflammation resolution is delayed and conditioning-lesion induced regeneration of DRG neuron central axons is abolished. Thus, carefully orchestrated inflammation resolution in the nerve is required for conditioning-lesion induced neurorepair.

neuroscience↗