Publications

Extracellular vesicles (EVs) are potent mediators in cell-cell communication that regulate diverse cell functions through the delivery of their bioactive cargo molecules to recipient cells. Previous work from our group demonstrated elevated plasma EV levels in patients and animals following septic or inflammatory insults, with a substantial proportion originating from neutrophils. As frontline defenders against bacterial infection, activated neutrophils release germicidal factors, some of which circulate systemically and inflict collateral tissue damage at a distance, including the brain. The role of neutrophil-derived EVs in regulating blood-brain barrier (BBB) structure and permeability after septic injury remains poorly defined. In this study, we first characterized EV production by mouse neutrophils stimulated with bacterial lipopolysaccharide (LPS) and subsequently investigated their functional and mechanistic effects on BBB integrity under in vivo and in vitro settings. Nanoparticle tracking analysis (NTA), immunoblotting, and transmission electron microscopy (TEM) revealed that LPS stimulation of neutrophils promoted EV secretion, indicated by increased particle number and protein content. Systemic administration of these EVs in mice induced cerebral microvascular leakage of plasma tracers (sodium fluorescein, at 376-Da; and dextran at 3-kDa) as quantified by near-infrared (NIR) nano-imaging and fluorometric assays. In cultured brain microvascular endothelial monolayers, EVs from naïve unstimulated neutrophils exerted minimal effects, whereas EVs from LPS-stimulated neutrophils caused a concentration-dependent reduction in transendothelial electrical resistance (TER) and a significant increase in solute permeability, indicative of paracellular hyperpermeability. Confocal microscopy revealed that tight junction proteins claudin-5 and zonula occludens-1 (ZO-1), which normally form continuous belt-like structures at endothelial cell–cell contacts, appeared discontinuous or fragmented upon EV internalization. Consistently, endothelial cells exposed to activated neutrophil-derived EVs exhibited reduced expression of tight junction proteins. Furthermore, TEM of brain capillaries from EV-injected mice provided ultrastructural evidence of tight junction disruption. Collectively, these findings suggest that neutrophil activation in response to infection promotes BBB leakage through the release of EVs capable of compromising endothelial tight junction integrity.

Laminin, by interacting with its receptors (mainly integrins and dystroglycan), exerts a variety of important functions in multiple organs. Loss-of-function studies have described the essential roles of laminin receptors in both physiological and pathologic conditions. This review summarizes the pathology and loss-of-function phenotypes of laminin receptors, including integrin-α3, integrin-α6, integrin-α7, integrin-β1, integrin-β4, and dystroglycan, focusing on the skin, kidney, skeletal muscle, peripheral nervous system, mammary gland, lung, and heart. To explore the functional redundancy/compensation among different laminin receptors, the phenotypes of compound knockout mice are compared with that of single mutants. Next, key signaling pathways downstream of each laminin receptor are summarized and compared. In addition, key questions in the field and future directions are also discussed. The aim of this review was to provide a synthetic review on loss-of-function studies of laminin receptors and foster the formation and testing of new hypotheses in the field.

Heart failure with preserved ejection fraction (HFpEF) is an increasingly prevalent clinical challenge, particularly among aging and postmenopausal women. Emerging evidence highlights a significant role of adipose tissue, especially adipose tissue surrounding the heart, in the pathogenesis of HFpEF. Visceral fat depots function as endocrine and inflammatory organs. Coupled with hormonal changes during menopause, adipose tissue contributes to cellular senescence and myocardial dysfunction. This brief review summarizes the mechanistic links among adipose tissue, sex hormones, and depot-specific inflammation in HFpEF, and underscores potential targets for future research and therapeutic intervention. 

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disorder marked by the deposition of amyloid-beta (Aβ) peptides within the walls of small- and medium-sized cerebral vessels, including arteries and capillaries but rarely veins. This vascular amyloid burden compromises vessel integrity, causes hemorrhages, and contributes to cognitive decline. Efficient Aβ clearance is critical for preventing its pathological accumulation. Thus, understanding the molecular players within the vascular microenvironment is essential. Laminin, a key glycoprotein of the vascular basal lamina (BL), is fundamental to maintaining structural stability of the vessels and regulating interactions among endothelial cells, pericytes, and the extracellular matrix. However, controversial findings exist on how laminin regulates Aβ aggregation and clearance, with both inhibitory and facilitative effects reported. Genetic variations in laminin subunits, their cell-specific expression pattern, and BL remodeling during CAA further complicate this relationship. This review synthesizes current knowledge on vascular Aβ deposition and elimination in CAA, with a particular focus on the critical roles of the BL/laminin and ApoE in shaping the perivascular microenvironment. First, we introduce Aβ processing relevant to CAA and the mechanisms of Aβ clearance in the CNS. Next, laminin-Aβ interactions and their functions in Aβ clearance are summarized. Thirdly, laminin changes and BL remodeling in CAA are discussed. Finally, we discuss the knowledge gap in the field and fundamental questions that need to be answered in future research. Defining the functions of the BL and ApoE within the pathological context of Aβ-rich vasculature may yield new insights into CAA pathogenesis and reveal therapeutic targets to limit vascular amyloid accumulation. Our goal is to provide a concise review on this matter in order to facilitate new hypotheses in the field. 

Pericytes, which share markers with smooth muscle cells (SMCs), are heterogenous cells. Pericytes in the brain and skeletal muscle have different embryonic origins, representing distinct subpopulations. One challenge in the field is that there are no subpopulation-specific pericyte markers. Here, we compared the transcriptomes of muscle pericytes and SMCs, and identified 741 muscle pericyte-enriched genes and 564 muscle SMC-enriched genes. Gene ontology analysis uncovered distinct biological processes and molecular functions in muscle pericytes and SMCs. Interestingly, the Venn diagram revealed only one gene shared by brain and muscle pericytes, suggesting that they are indeed distinct subpopulations with different transcriptional profiles. We further validated that GSN co-localized with PDGFRβ⁺SMA⁻ cells in small and large blood vessels but not PDGFRβ⁺SMA⁺ cells, indicating that GSN predominantly marks pericytes and fibroblasts rather than SMCs in skeletal muscle. Negligible levels of GSN were detected in the brain. These findings indicate that GSN may serve as a selective marker for muscle pericytes.

Laminin exerts a variety of important functions via binding to its receptors, including integrins and dystroglycan. With the advance in gene-targeting technology, many integrin/dystroglycan knockout/mutant mice were generated in the past 3 decades. These mutants enable loss-of-function studies and have substantially enriched our knowledge of integrin/dystroglycan functions. In this review, we summarize the functions of laminin receptors during embryonic development and in the central nervous system and vasculature. First, the biochemical properties of integrins and dystroglycan are briefly introduced. Next, we discuss loss-of-function studies on laminin receptors, including integrin-α3, integrin-α6, integrin-α7, integrin-β1, integrin-β4, and dystroglycan, focusing on embryonic development, the central nervous system, and vasculature. The phenotypes of compound knockout mice are described and compared with that of single mutants. Last, important questions and challenges in the field as well as potential future directions are discussed. Our goal is to provide a synthetic review on loss-of-function studies of laminin receptors in the central nervous system and vasculature, which could serve as a reference for future research, encourage the formation of new hypotheses, and stimulate new research in this field.

The blood-brain barrier (BBB) is a dynamic structure that maintains brain homeostasis. BBB breakdown is a key pathological hallmark of almost all neurological diseases. Although the regulation of BBB integrity by different cells has been extensively studied, the function of its non-cellular component-the basal lamina in BBB regulation remains largely unknown. Laminin, a trimeric protein with multiple isoforms, is one of the most important constituents of the basal lamina. In the CNS, different cells synthesize distinct laminin isoforms, which differentially regulate BBB integrity in both physiological and pathological conditions. A thorough understanding of laminin expression and function in BBB integrity could lead to the identification of novel therapeutic targets and potentially result in effective treatments for neurological disorders involving BBB disruption. Here in this review, we first briefly introduce the BBB and basal lamina with a focus on laminin. Next, we elucidate laminin expression and its function in BBB maintenance/repair in a cell-specific manner. Potential functional compensation among laminin isoforms is also discussed. Last, current challenges in the field and future directions are summarized. Our goal is to provide a synthetic review to encourage novel ideas and stimulate new research in the field.

Intracerebral hemorrhage (ICH), the deadliest form of stroke, is characterized by bleeding into brain parenchyma and formation of hematoma. Currently, there is no treatment available for ICH. Inflammatory response is a key pathology of ICH and plays a dual role in ICH---contributing to both secondary brain injury and recovery processes. This review discusses different types (both brain-resident and infiltrated) of immune cells and their functions during inflammation processes following ICH. Specifically, the temporal dynamics, polarization, and function of microglia/macrophages, neutrophils, lymphocytes, and astrocytes in ICH are summarized in a cell-specific manner. In addition, we also discuss key challenges and unanswered questions that need to be addressed in the future. A thorough understanding of the functions of different immune cells in ICH will provide a strong foundation for future studies and lead to the identification of novel cellular/molecular targets for therapeutic development.

Background: Pericytes, a type of mural cells, exert important functions in the CNS. One major challenge in pericyte research is the lack of pericyte-specific and subpopulation-specific markers.

Methods: To address this knowledge gap, we first generated a novel transgenic mouse line in which vascular smooth muscle cells (vSMCs) are permanently labeled with tdTomato. Next, we isolated PDGFRβ⁺tdTomato^- pericytes and PDGFRβ⁺tdTomato⁺ vSMCs from the brains of these mice and subsequently performed RNAseq analysis to identify pericyte-enriched genes.

Results: Using this approach, we successfully identified 40 pericyte-enriched genes and 158 vSMC-enriched genes, which are involved in different biological processes and molecular functions. Using ISH/IHC analysis, we found that Pla1a and Cox4i2 were predominantly enriched in subpopulations of brain pericytes, although they also marked some non-vascular parenchymal cells.

Conclusions: These findings suggest that Pla1a and Cox4i2 preferably label subpopulations of pericytes in the brain compared to vSMCs, and thus, they may be useful in distinguishing these populations.

Although oligodendrocytes (OLs) synthesize laminin-γ1, the most widely used γ subunit, its functional significance in the CNS remains unknown. To answer this important question, we generated a conditional knockout mouse line with laminin-γ1 deficiency in OL lineage cells (γ1-OKO). γ1-OKO mice exhibit weakness/paralysis and die by post-natal day 33. Additionally, they develop blood-brain barrier (BBB) disruption in the cortex and striatum. Subsequent studies reveal decreased major facilitator superfamily domain containing 2a expression and increased endothelial caveolae vesicles, but unaltered tight junction protein expression and tight junction ultrastructure, indicating a transcellular, rather than a paracellular, mechanism of BBB breakdown. Furthermore, significantly reduced OL lineage cells, OL precursor cells (OPCs), proliferating OPCs, and mature OLs are observed in γ1-OKO brains in a region-specific manner. Consistent with this finding, various defects in myelination are detected in γ1-OKO brains at biochemical and ultrastructural levels. Overall, these results highlight important roles of OL-derived laminin-γ1 in BBB maintenance and OL biology (proliferation, differentiation, and myelination).