Mesenchymal Stromal Cells Promote Axonal Outgrowth Alone and Synergistically with Astrocytes via tPA

The molecular mechanism of LRP1 in physiological vascular homeostasis and signal transduction pathways

Interactions between vascular smooth muscle cells (VSMCs), endothelial cells (ECs), pericytes (PCs) and macrophages (MФ), the major components of blood vessels, play a crucial role in maintaining vascular structural and functional homeostasis. Low-density lipoprotein (LDL) receptor-related protein-1 (LRP1), a transmembrane receptor protein belonging to the LDL receptor family, plays multifunctional roles in maintaining endocytosis, homeostasis, and signal transduction. Accumulating evidence suggests that LRP1 modulates vascular homeostasis mainly by regulating vasoactive substances and specific intracellular signaling pathways, including the plasminogen activator inhibitor 1 (PAI-1) signaling pathway, platelet-derived growth factor (PDGF) signaling pathway, transforming growth factor-β (TGF-β) signaling pathway and vascular endothelial growth factor (VEGF) signaling pathway. The aim of the present review is to focus on recent advances in the discovery and mechanism of vascular homeostasis regulated by LRP1-dependent signaling pathways. These recent discoveries expand our understanding of the mechanisms controlling LRP1 as a target for studies on vascular complications.

Targeted tPA overexpression in denervated spinal motor neurons promotes stroke recovery in mice

Our previous studies demonstrated that axonal remodeling of the corticospinal tract (CST) contributes to neurological recovery after stroke in rodents. The present study employed a novel non-invasive peripheral approach, to over-express tPA in denervated spinal motor neurons via recombinant adeno-associated virus (AAV) intramuscular injection in transgenic mice subjected to permanent middle cerebral artery occlusion (MCAo), in which the CST axons are specifically and completely labeled with yellow fluorescent protein (YFP). One day after surgery, mice were randomly selected to receive saline, AAV5-RFP, or tPA (1 × 10¹⁰ viral particles) injected into the stroke-impaired forelimb muscles (n = 10/group). Functional deficits and recovery were monitored with foot-fault and single pellet reaching tests. At day 28 after MCAo, mice received intramuscular injection of PRV-614-mRFP (1.52 × 10⁷ pfu) as above, and were euthanized four days later. Compared with saline or AAV-RFP-treated mice, AAV-tPA significantly enhanced behavioral recovery (p < 0.01, both tests), as well as increased CST axonal density in the denervated gray matter of the cervical cord (p < 0.001), and RFP-positive pyramidal neurons in both ipsilesional and contralesional cortices (p < 0.001). Behavioral outcomes were significantly correlated to neural remodeling (p < 0.05). Our results provide a fundamental basis for the development of therapeutic approaches aimed at promoting corticospinal innervation for stroke treatment.

Mesenchymal stem cells instruct a beneficial phenotype in reactive astrocytes

Transplanted mesenchymal stromal/stem cells (MSC) ameliorate the clinical course of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS), reducing inflammation and demyelination. These effects are mediated by instructive cross-talk between MSC and immune and neural cells. Astroglial reaction to injury is a prominent feature of both EAE and MS. Astrocytes constitute a relevant target to control disease onset and progression and, based on their potential to acquire stem cell properties in situ, to foster recovery in the post-acute phase of pathology. We have assessed how MSC impact astrocytes in vitro and ex vivo in EAE. Expression of astroglial factors implicated in EAE pathogenesis was quantified by real-time PCR in astrocytes co-cultured with MSC or isolated from EAE cerebral cortex; astrocyte morphology and expression of activation markers were analyzed by confocal microscopy. The acquisition of neural stem cell properties by astrocytes was evaluated by neurosphere assay. Our study shows that MSC prevented astrogliosis, reduced mRNA expression of inflammatory cytokines that sustain immune cell infiltration in EAE, as well as protein expression of endothelin-1, an astrocyte-derived factor that inhibits remyelination and contributes to neurodegeneration and disease progression in MS. Moreover, our data reveal that MSC promoted the acquisition of progenitor traits by astrocytes. These data indicate that MSC attenuate detrimental features of reactive astroglia and, based on the reacquisition of stem cell properties, also suggest that astrocytes may be empowered in their protective and reparative actions by MSC.

Advances in ex vivo models and lab-on-a-chip devices for neural tissue engineering

The technologies related to ex vivo models and lab-on-a-chip devices for studying the regeneration of brain, spinal cord, and peripheral nerve tissues are essential tools for neural tissue engineering and regenerative medicine research. The need for ex vivo systems, lab-on-a-chip technologies and disease models for neural tissue engineering applications are emerging to overcome the shortages and drawbacks of traditional in vitro systems and animal models. Ex vivo models have evolved from traditional 2D cell culture models to 3D tissue-engineered scaffold systems, bioreactors, and recently organoid test beds. In addition to ex vivo model systems, we discuss lab-on-a-chip devices and technologies specifically for neural tissue engineering applications. Finally, we review current commercial products that mimic diseased and normal neural tissues, and discuss the future directions in this field.

Subacute intranasal administration of tissue plasminogen activator improves stroke recovery by inducing axonal remodeling in mice

In addition to thrombolysis, tissue plasminogen activator (tPA) can evoke neurorestorative processes. We therefore investigated the therapeutic effect of subacute intranasal administration of tPA post stroke on neurological recovery and on corticospinal innervation in mice. A transgenic mouse line, in which the pyramidal neurons and corticospinal tract (CST) axons are specifically labeled by yellow fluorescent protein (YFP) was employed. Adult CST-YFP mice were subjected to right unilateral middle cerebral artery occlusion (MCAo), and were randomly divided into groups treated with saline or tPA intranasally in the subacute phase. Pseudorabies virus (PRV)-614-monomeric red fluorescent protein (RFP) was injected into the left forelimb. The cervical spinal cord and brain were processed for fluorescent microscopy to detect YFP and RFP labeling. Primary embryonic neurons were cultured with tPA at different concentrations. Neurite length and branch numbers were then measured. In vivo, subacute tPA treatment significantly enhanced functional recovery (p < 0.05), and increased CST density in the denervated gray matter, and in the numbers of PRV-labeled neurons in bilateral cortices. The behavioral performance was significantly correlated with axonal density in the denervated spinal cord. In vitro, both neurite length and branch numbers significantly increased with concentration of tPA (p < 0.05). Our results demonstrate that tPA dose-dependently increases neurite outgrowth and branching of cultured cortical neurons. Subacute intranasal administration of tPA may provide enhance neurological recovery after stroke by promoting CST axonal remodeling.