Schwann cell-specific deletion of the endosomal PI 3-kinase Vps34 leads to delayed radial sorting of axons, arrested myelination, and abnormal ErbB2-ErbB3 tyrosine kinase signaling

Autophagy-targeting modulation to promote peripheral nerve regeneration

Nerve regeneration following traumatic peripheral nerve injuries and neuropathies is a complex process modulated by diverse factors and intricate molecular mechanisms. Past studies have focused on factors that stimulate axonal outgrowth and myelin regeneration. However, recent studies have highlighted the pivotal role of autophagy in peripheral nerve regeneration, particularly in the context of traumatic injuries. Consequently, autophagy-targeting modulation has emerged as a promising therapeutic approach to enhancing peripheral nerve regeneration. Our current understanding suggests that activating autophagy facilitates the rapid clearance of damaged axons and myelin sheaths, thereby enhancing neuronal survival and mitigating injury-induced oxidative stress and inflammation. These actions collectively contribute to creating a favorable microenvironment for structural and functional nerve regeneration. A range of autophagy-inducing drugs and interventions have demonstrated beneficial effects in alleviating peripheral neuropathy and promoting nerve regeneration in preclinical models of traumatic peripheral nerve injuries. This review delves into the regulation of autophagy in cell types involved in peripheral nerve regeneration, summarizing the potential drugs and interventions that can be harnessed to promote this process. We hope that our review will offer novel insights and perspectives on the exploitation of autophagy pathways in the treatment of peripheral nerve injuries and neuropathies.

Maternal omega-3 polyunsaturated fatty acids improved levels of DHA-enriched phosphatidylethanolamines and enriched lipid clustering in the neuronal membranes of C57BL/6 mice fetal brains during gestation

The composition of brain lipids is crucial for neurodevelopment and brain function. Diets enriched in omega (n)-3 polyunsaturated fatty acids (PUFA) can modulate brain lipid composition. However, the influence of maternal n-3 PUFA intake on fetal brain lipidome and neuronal membrane structure during gestation is not well studied. Eight-week-old female C57BL/6 mice were fed low or high n-3 PUFA semi-purified diets for two weeks before mating and during gestation. Fetal brain lipidome and neuronal membrane structure were studied at gestation day (GD) 12.5 (mid) and 18.5 (late) using liquid chromatography high-resolution accurate mass tandem mass spectrometry and computational techniques. Maternal diets high in n-3 PUFA increased fetal brain total phosphoethanolamine, phosphoinositol, phosphoglycerol, and phosphoserine glycerophospholipids, compared to the low n-3 PUFA diet. Docosahexaenoic acid (DHA, 22:6n-3)-enriched phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and lyso-PC (LPC) fatty acyl species increased as gestation progressed in the high n-3 PUFA group, compared to low n-3 PUFA. These fatty acyl species and phospholipids promote neurotransmission, memory, and cognition. A high n-3 PUFA diet increased the area per lipid in fetal neuronal membranes as gestation progressed, indicating improved membrane fluidity. Furthermore, a high n-3 PUFA diet increased the clustering of membrane lipids associated with neurotransmission, memory, and cognition (ceramide, PE, and cholesteryl ester) as gestation progressed. Our findings show for the first time that maternal diets high in n-3 PUFA before and during gestation improve fetal brain lipidome and membrane area per lipid that may enhance brain development and function.

Schwann Cell-Specific Ablation of Beclin 1 Impairs Myelination and Leads to Motor and Sensory Neuropathy in Mice

The core component of the class III phosphatidylinositol 3-kinase complex, Beclin 1, takes part in different protein networks, thus switching its role from inducing autophagy to regulating autophagosomal maturation and endosomal trafficking. While assessed in neurons, astrocytes, and microglia, its role is far less investigated in myelinating glia, including Schwann cells (SCs), responsible for peripheral nerve myelination. Remarkably, the dysregulation in endosomal trafficking is emerging as a pathophysiological mechanism underlying peripheral neuropathies, such as demyelinating Charcot-Marie-Tooth (CMT) diseases. By knocking out Beclin 1 in SCs here a novel mouse model (Becn1 cKO) is generated, developing a severe and progressive neuropathy, accompanied by involuntary tremors, body weight loss, and premature death. Ultrastructural analysis revealed abated myelination and SCs displaying enlarged cytoplasm with progressive accumulation of intracellular vesicles. Transcriptomic and histological analysis from sciatic nerves of 10-day and 2-month-old mice revealed pro-mitotic gene deregulation and increased SCs proliferation at both stages with axonal loss and increased immune infiltration in adults, well reflecting the progressive motor and sensory functional impairment that characterizes Becn1 cKO mice, compared to controls. The study establishes a further step in understanding key mechanisms in SC development and points to Beclin 1 and its regulated pathways as targets for demyelinating CMT forms.

VPS34 Governs Oocyte Developmental Competence by Regulating Mito/Autophagy: A Novel Insight into the Significance of RAB7 Activity and Its Subcellular Location

Asynchronous nuclear and cytoplasmic maturation in human oocytes is believed to cause morphological anomalies after controlled ovarian hyperstimulation. Vacuolar protein sorting 34 (VPS34) is renowned for its pivotal role in regulating autophagy and endocytic trafficking. To investigate its impact on oocyte development, oocyte-specific knockout mice (ZcKO) are generated, and these mice are completely found infertile, with embryonic development halted at 2- to 4-cell stage. This infertility is related with a disruption on autophagic/mitophagic flux in ZcKO oocytes, leading to subsequent failure of zygotic genome activation (ZGA) in derived 2-cell embryos. The findings further elucidated the regulation of VPS34 on the activity and subcellular translocation of RAS-related GTP-binding protein 7 (RAB7), which is critical not only for the maturation of late endosomes and lysosomes, but also for initiating mitophagy via retrograde trafficking. VPS34 binds directly with RAB7 and facilitates its activity conversion through TBC1 domain family member 5 (TBC1D5). Consistent with the cytoplasmic vacuolation observed in ZcKO oocytes, defects in multiple vesicle trafficking systems are also identified in vacuolated human oocytes. Furthermore, activating VPS34 with corynoxin B (CB) treatment improved oocyte quality in aged mice. Hence, VPS34 activation may represent a novel approach to enhance oocyte quality in human artificial reproduction.

Review: Myelin clearance is critical for regeneration after peripheral nerve injury

Traumatic peripheral nerve injury occurs frequently and is a major clinical and public health problem that can lead to functional impairment and permanent disability. Despite the availability of modern diagnostic procedures and advanced microsurgical techniques, active recovery after peripheral nerve repair is often unsatisfactory. Peripheral nerve regeneration involves several critical events, including the recreation of the microenvironment and remyelination. Results from previous studies suggest that the peripheral nervous system (PNS) has a greater capacity for repair than the central nervous system. Thus, it will be important to understand myelin and myelination specifically in the PNS. This review provides an update on myelin biology and myelination in the PNS and discusses the mechanisms that promote myelin clearance after injury. The roles of Schwann cells and macrophages are considered at length, together with the possibility of exogenous intervention.

Disruption of Endosomal Sorting in Schwann Cells Leads to Defective Myelination and Endosomal Abnormalities Observed in Charcot-Marie-Tooth Disease

Endosomal sorting plays a fundamental role in directing neural development. By altering the temporal and spatial distribution of membrane receptors, endosomes regulate signaling pathways that control the differentiation and function of neural cells. Several genes linked to inherited demyelinating peripheral neuropathies, known as Charcot-Marie-Tooth (CMT) disease, encode proteins that directly interact with components of the endosomal sorting complex required for transport (ESCRT). Our previous studies demonstrated that a point mutation in the ESCRT component hepatocyte growth-factor-regulated tyrosine kinase substrate (HGS), an endosomal scaffolding protein that identifies internalized cargo to be sorted by the endosome, causes a peripheral neuropathy in the neurodevelopmentally impaired teetering mice. Here, we constructed a Schwann cell-specific deletion of Hgs to determine the role of endosomal sorting during myelination. Inactivation of HGS in Schwann cells resulted in motor and sensory deficits, slowed nerve conduction velocities, delayed myelination and hypomyelinated axons, all of which occur in demyelinating forms of CMT. Consistent with a delay in Schwann cell maturation, HGS-deficient sciatic nerves displayed increased mRNA levels for several promyelinating genes and decreased mRNA levels for genes that serve as markers of myelinating Schwann cells. Loss of HGS also altered the abundance and activation of the ERBB2/3 receptors, which are essential for Schwann cell development. We therefore hypothesize that HGS plays a critical role in endosomal sorting of the ERBB2/3 receptors during Schwann cell maturation, which further implicates endosomal dysfunction in inherited peripheral neuropathies.SIGNIFICANCE STATEMENT Schwann cells myelinate peripheral axons, and defects in Schwann cell function cause inherited demyelinating peripheral neuropathies known as CMT. Although many CMT-linked mutations are in genes that encode putative endosomal proteins, little is known about the requirements of endosomal sorting during myelination. In this study, we demonstrate that loss of HGS disrupts the endosomal sorting pathway in Schwann cells, resulting in hypomyelination, aberrant myelin sheaths, and impairment of the ERBB2/3 receptor pathway. These findings suggest that defective endosomal trafficking of internalized cell surface receptors may be a common mechanism contributing to demyelinating CMT.

Aberrant Neuregulin 1/ErbB Signaling in Charcot-Marie-Tooth Type 4D Disease

Charcot-Marie-Tooth type 4D (CMT4D) is an autosomal recessive demyelinating form of CMT characterized by progressive motor and sensory neuropathy. N-myc downstream regulated gene 1 (NDRG1) is the causative gene for CMT4D. Although more CMT4D cases have been reported, the comprehensive molecular mechanism underlying CMT4D remains elusive. Here, we generated a novel knockout mouse model in which the fourth and fifth exons of the Ndrg1 gene were removed. Ndrg1-deficient mice develop early progressive demyelinating neuropathy and limb muscle weakness. The expression pattern of myelination-related transcriptional factors, including SOX10, OCT6, and EGR2, was abnormal in Ndrg1-deficient mice. We further investigated the activation of the ErbB2/3 receptor tyrosine kinases in Ndrg1-deficient sciatic nerves, as these proteins play essential roles in Schwann cell myelination. In the absence of NDRG1, although the total ErbB2/3 receptors expressed by Schwann cells were significantly increased, levels of the phosphorylated forms of ErbB2/3 and their downstream signaling cascades were decreased. This change was not associated with the level of the neuregulin 1 ligand, which was increased in Ndrg1-deficient mice. In addition, the integrin β4 receptor, which interacts with ErbB2/3 and positively regulates neuregulin 1/ErbB signaling, was significantly reduced in the Ndrg1-deficient nerve. In conclusion, our data suggest that the demyelinating phenotype of CMT4D disease is at least in part a consequence of molecular defects in neuregulin 1/ErbB signaling.

Down Syndrome Fetal Fibroblasts Display Alterations of Endosomal Trafficking Possibly due to SYNJ1 Overexpression

Endosomal trafficking is essential for cellular homeostasis. At the crossroads of distinct intracellular pathways, the endolysosomal system is crucial to maintain critical functions and adapt to the environment. Alterations of endosomal compartments were observed in cells from adult individuals with Down syndrome (DS), suggesting that the dysfunction of the endosomal pathway may contribute to the pathogenesis of DS. However, the nature and the degree of impairment, as well as the timing of onset, remain elusive. Here, by applying imaging and biochemical approaches, we demonstrate that the structure and dynamics of early endosomes are altered in DS cells. Furthermore, we found that recycling trafficking is markedly compromised in these cells. Remarkably, our results in 18–20 week-old human fetal fibroblasts indicate that alterations in the endolysosomal pathway are already present early in development. In addition, we show that overexpression of the polyphosphoinositide phosphatase synaptojanin 1 (Synj1) recapitulates the alterations observed in DS cells, suggesting a role for this lipid phosphatase in the pathogenesis of DS, likely already early in disease development. Overall, these data strengthen the link between the endolysosomal pathway and DS, highlighting a dangerous liaison among Synj1, endosomal trafficking and DS.

Distinct roles for the Charcot-Marie-tooth disease-causing endosomal regulators Mtmr5 and Mtmr13 in axon radial sorting and Schwann cell myelination

The form of Charcot-Marie-Tooth type 4B (CMT4B) disease caused by mutations in myotubularin-related 5 (MTMR5; also called SET Binding Factor 1; SBF1) shows a spectrum of axonal and demyelinating nerve phenotypes. This contrasts with the CMT4B subtypes caused by MTMR2 or MTMR13 (SBF2) mutations, which are characterized by myelin outfoldings and classic demyelination. Thus, it is unclear whether MTMR5 plays an analogous or distinct role from that of its homolog, MTMR13, in the peripheral nervous system (PNS). MTMR5 and MTMR13 are pseudophosphatases predicted to regulate endosomal trafficking by activating Rab GTPases and binding to the phosphoinositide 3-phosphatase MTMR2. In the mouse PNS, Mtmr2 was required to maintain wild type levels of Mtmr5 and Mtmr13, suggesting that these factors function in discrete protein complexes. Genetic elimination of both Mtmr5 and Mtmr13 in mice led to perinatal lethality, indicating that the two proteins have partially redundant functions during embryogenesis. Loss of Mtmr5 in mice did not cause CMT4B-like myelin outfoldings. However, adult Mtmr5-/- mouse nerves contained fewer myelinated axons than control nerves, likely as a result of axon radial sorting defects. Consistently, Mtmr5 levels were highest during axon radial sorting and fell sharply after postnatal day seven. Our findings suggest that Mtmr5 and Mtmr13 ensure proper axon radial sorting and Schwann cell myelination, respectively, perhaps through their direct interactions with Mtmr2. This study enhances our understanding of the non-redundant roles of the endosomal regulators MTMR5 and MTMR13 during normal peripheral nerve development and disease.

Peripheral Nerve Development and the Pathogenesis of Peripheral Neuropathy: the Sorting Point

Nerve development requires a coordinated sequence of events and steps to be accomplished for the generation of functional peripheral nerves to convey sensory and motor signals. Any abnormality during development may result in pathological structure and function of the nerve, which evolves in peripheral neuropathy. In this review, we will briefly describe different steps of nerve development while we will mostly focus on the molecular mechanisms involved in radial sorting of axons, one of these nerve developmental steps. We will summarize current knowledge of molecular pathways so far reported in radial sorting and their possible interactions. Finally, we will describe how disruption of these pathways may result in human neuropathies.

Protective effect and potential mechanism of Schwann cell-derived exosomes on mechanical damage of rat dorsal root ganglion cells

BACKGROUND

Pudendal nerve (PN) injury was one of the most important pathogenesis of stress urinary incontinence (SUI). Schwann cell (SC)-derived exosomes could promote axonal regeneration. Wnt protein could significantly promote axonal regeneration and participate in the regulation of proliferation and differentiation of neural stem cells. Therefore, we sought to determine whether SCs-derived exosomes might also protect against damaged dorsal root ganglion cells (DRGs) through the Wnt/β-catenin pathway.

MATERIAL AND METHODS

The DRGs injury model was fabricated using a four-point bending system. The exosomes were separated from the SCs supernatant. XAV939, which was a small molecule inhibitor, was used to inhibit the Wnt/β-catenin pathway. Next, Cell Counting Kit-8 (CCK8) kit was used to detect cell activity. We evaluated the proliferative activity of DRG cells using the cell cycle and apoptosis detection kit. We assessed the cell apoptotic rates through the Annexin V/PE double staining. Finally, we detect the expression of downstream proteins of Wnt/β-catenin pathway in DRG cells using western blotting.

RESULTS

SC-derived exosomes had protective effects on DRGs after mechanical damage, which could promote cell proliferation, transition of the cell cycle to the G2 phase, and inhibit cell apoptosis. Exogenous administration of XAV939 suppressed the promoting effect of SCs -derived exosomes on DRG cells and the expression of downstream proteins of Wnt/β-catenin pathway in DRG cells was also suppressed.

CONCLUSION

These results suggested that SC-derived exosomes have a repairing effect on DRG cells injury caused by cyclic mechanical stretching (CMS) and the Wnt/β-catenin pathway is potentially involved in the process.

Autophagy and ALS: mechanistic insights and therapeutic implications

Mechanisms of protein homeostasis are crucial for overseeing the clearance of misfolded and toxic proteins over the lifetime of an organism, thereby ensuring the health of neurons and other cells of the central nervous system. The highly conserved pathway of autophagy is particularly necessary for preventing and counteracting pathogenic insults that may lead to neurodegeneration. In line with this, mutations in genes that encode essential autophagy factors result in impaired autophagy and lead to neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). However, the mechanistic details underlying the neuroprotective role of autophagy, neuronal resistance to autophagy induction, and the neuron-specific effects of autophagy-impairing mutations remain incompletely defined. Further, the manner and extent to which non-cell autonomous effects of autophagy dysfunction contribute to ALS pathogenesis are not fully understood. Here, we review the current understanding of the interplay between autophagy and ALS pathogenesis by providing an overview of critical steps in the autophagy pathway, with special focus on pivotal factors impaired by ALS-causing mutations, their physiologic effects on autophagy in disease models, and the cell type-specific mechanisms regulating autophagy in non-neuronal cells which, when impaired, can contribute to neurodegeneration. This review thereby provides a framework not only to guide further investigations of neuronal autophagy but also to refine therapeutic strategies for ALS and related neurodegenerative diseases.Abbreviations: ALS: amyotrophic lateral sclerosis; Atg: autophagy-related; CHMP2B: charged multivesicular body protein 2B; DPR: dipeptide repeat; FTD: frontotemporal dementia; iPSC: induced pluripotent stem cell; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PINK1: PTEN induced kinase 1; RNP: ribonuclear protein; sALS: sporadic ALS; SPHK1: sphingosine kinase 1; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase; UPR: unfolded protein response; UPS: ubiquitin-proteasome system; VCP: valosin containing protein.

Neuroglial transmitophagy and Parkinson's disease

Mitophagy is essential for the health of dopaminergic neurons because mitochondrial damage is a keystone of Parkinson's disease. The aim of the present work was to study the degradation of mitochondria in the degenerating dopaminergic synapse. Adult Sprague-Dawley rats and YFP-Mito-DAn mice with fluorescent mitochondria in dopaminergic neurons were injected in the lateral ventricles with 6-hydroxydopamine, a toxic that inhibits the mitochondrial chain of dopaminergic neurons and blockades the axonal transport. Dopaminergic terminals closest to the lateral ventricle showed an axonal fragmentation and an accumulation of damaged mitochondria in 2-9 μ saccular structures (spheroids). Damaged mitochondria accumulated in spheroids initiated (showing high Pink1, parkin, ubiquitin, p-S65-Ubi, AMBRA1, and BCL2L13 immunoreactivity and developing autophagosomes) but did not complete (mitochondria were not polyubiquitinated, autophagosomes had no STX17, and no lysosomes were found in spheroids) the mitophagy process. Then, spheroids were penetrated by astrocytic processes and DAergic mitochondria were transferred to astrocytes where they were polyubiquitinated (UbiK63+) and linked to mature autophagosomes (STX17+) which became autophagolysosomes (Lamp1/Lamp2 which co-localized with LC3). Present data provide evidence that the mitophagy of degenerating dopaminergic terminals starts in the dopaminergic spheroids and finishes in the surrounding astrocytes (spheroid-mediated transmitophagy). The neuron-astrocyte transmitophagy could be critical for preventing the release of damaged mitochondria to the extracellular medium and the neuro-inflammatory activity which characterizes Parkinson's disease.

PI3K inhibitors in thrombosis and cardiovascular disease

Phosphoinositide 3-kinases (PI3Ks) are lipid kinases that regulate important intracellular signalling and vesicle trafficking events via the generation of 3-phosphoinositides. Comprising eight core isoforms across three classes, the PI3K family displays broad expression and function throughout mammalian tissues, and the (patho)physiological roles of these enzymes in the cardiovascular system present the PI3Ks as potential therapeutic targets in settings such as thrombosis, atherosclerosis and heart failure. This review will discuss the PI3K enzymes and their roles in cardiovascular physiology and disease, with a particular focus on platelet function and thrombosis. The current progress and future potential of targeting the PI3K enzymes for therapeutic benefit in cardiovascular disease will be considered, while the challenges of developing drugs against these master cellular regulators will be discussed.

Axo-glial interdependence in peripheral nerve development

During the development of the peripheral nervous system, axons and myelinating Schwann cells form a unique symbiotic unit, which is realized by a finely tuned network of molecular signals and reciprocal interactions. The importance of this complex interplay becomes evident after injury or in diseases in which aspects of axo-glial interaction are perturbed. This Review focuses on the specific interdependence of axons and Schwann cells in peripheral nerve development that enables axonal outgrowth, Schwann cell lineage progression, radial sorting and, finally, formation and maintenance of the myelin sheath.

Phosphoinositides: Regulators of Nervous System Function in Health and Disease

Phosphoinositides, the seven phosphorylated derivatives of phosphatidylinositol have emerged as regulators of key sub-cellular processes such as membrane transport, cytoskeletal function and plasma membrane signaling in eukaryotic cells. All of these processes are also present in the cells that constitute the nervous system of animals and in this setting too, these are likely to tune key aspects of cell biology in relation to the unique structure and function of neurons. Phosphoinositides metabolism and function are mediated by enzymes and proteins that are conserved in evolution, and analysis of knockouts of these in animal models implicate this signaling system in neural function. Most recently, with the advent of human genome analysis, mutations in genes encoding components of the phosphoinositide signaling pathway have been implicated in human diseases although the cell biological basis of disease phenotypes in many cases remains unclear. In this review we evaluate existing evidence for the involvement of phosphoinositide signaling in human nervous system diseases and discuss ways of enhancing our understanding of the role of this pathway in the human nervous system's function in health and disease.

An In Vitro Model of Charcot-Marie-Tooth Disease Type 4B2 Provides Insight Into the Roles of MTMR13 and MTMR2 in Schwann Cell Myelination

Charcot-Marie-Tooth Disorder Type 4B (CMT4B) is a demyelinating peripheral neuropathy caused by mutations in myotubularin-related (MTMR) proteins 2, 13, or 5 (CMT4B1/2/3), which regulate phosphoinositide turnover and endosomal trafficking. Although mouse models of CMT4B2 exist, an in vitro model would make possible pharmacological and reverse genetic experiments needed to clarify the role of MTMR13 in myelination. We have generated such a model using Schwann cell-dorsal root ganglion (SC-DRG) explants from Mtmr13-/- mice. Myelin sheaths in mutant cultures contain outfoldings highly reminiscent of those observed in the nerves of Mtmr13-/- mice and CMT4B2 patients. Mtmr13-/- SC-DRG explants also contain reduced Mtmr2, further supporting a role of Mtmr13 in stabilizing Mtmr2. Elevated PI(3,5)P2 has been implicated as a cause of myelin outfoldings in Mtmr2-/- models. In contrast, the role of elevated PI3P or PI(3,5)P2 in promoting outfoldings in Mtmr13-/- models is unclear. We found that over-expression of MTMR2 in Mtmr13-/- SC-DRGs moderately reduced the prevalence of myelin outfoldings. Thus, a manipulation predicted to lower PI3P and PI(3,5)P2 partially suppressed the phenotype caused by Mtmr13 deficiency. We also explored the relationship between CMT4B2-like myelin outfoldings and kinases that produce PI3P and PI(3,5)P2 by analyzing nerve pathology in mice lacking both Mtmr13 and one of two specific PI 3-kinases. Intriguingly, the loss of vacuolar protein sorting 34 or PI3K-C2β in Mtmr13-/- mice had no impact on the prevalence of myelin outfoldings. In aggregate, our findings suggest that the MTMR13 scaffold protein likely has critical functions other than stabilizing MTMR2 to achieve an adequate level of PI 3-phosphatase activity.

Ulk4 deficiency leads to hypomyelination in mice

Brain nerve fibers are insulated by myelin which is produced by oligodendrocytes. Defects in myelination are increasingly recognized as a common pathology underlying neuropsychiatric and neurodevelopmental disorders, which are associated with deletions of the Unc-51-like kinase 4 (ULK4) gene. Key transcription factors have been identified for oligodendrogenesis, but little is known about their associated regulators. Here we report that Ulk4 acts as a key regulator of myelination. Myelination is reduced by half in the Ulk4^tm1a/tm1a hypomorph brain, whereas expression of axonal marker genes Tubb3, Nefh, Nefl and Nefm remains unaltered. Transcriptome analyses reveal that 8 (Gfap, Mbp, Mobp, Plp1, Slc1a2, Ttr, Cnp, Scd2) of the 10 most significantly altered genes in the Ulk4^tm1a/tm1a brain are myelination-related. Ulk4 is co-expressed in Olig2⁺ (pan-oligodendrocyte marker) and CC1⁺ (mature myelinated oligodendrocyte marker) cells during postnatal development. Major oligodendrogeneic transcription factors, including Olig2, Olig1, Myrf, Sox10, Sox8, Sox6, Sox17, Nkx2-2, Nkx6-2 and Carhsp1, are significantly downregulated in the mutants. mRNA transcripts enriched in oligodendrocyte progenitor cells (OPCs), the newly formed oligodendrocytes (NFOs) and myelinating oligodendrocytes (MOs), are significantly attenuated. Expression of stage-specific oligodendrocyte factors including Cspg4, Sox17, Nfasc, Enpp6, Sirt2, Cnp, Plp1, Mbp, Ugt8, Mag and Mog are markedly decreased. Indirect effects of axon caliber and neuroinflammation may also contribute to the hypomyelination, as Ulk4 mutants display smaller axons and increased neuroinflammation. This is the first evidence demonstrating that ULK4 is a crucial regulator of myelination, and ULK4 may therefore become a novel therapeutic target for hypomyelination diseases.