Platelet-Derived Growth Factor Subunit B Signaling Promotes Pericyte Migration in Response to Loud Sound in the Cochlear Stria Vascularis

Multiscale computational model predicts how environmental changes and drug treatments affect microvascular remodeling in fibrotic disease

Investigating the molecular, cellular, and tissue-level changes caused by disease, and the effects of pharmacological treatments across these biological scales, necessitates the use of multiscale computational modeling in combination with experimentation. Many diseases dynamically alter the tissue microenvironment in ways that trigger microvascular network remodeling, which leads to the expansion or regression of microvessel networks. When microvessels undergo remodeling in idiopathic pulmonary fibrosis (IPF), functional gas exchange is impaired due to loss of alveolar structures and lung function declines. Here, we integrated a multiscale computational model with independent experiments to investigate how combinations of biomechanical and biochemical cues in IPF alter cell fate decisions leading to microvascular remodeling. Our computational model predicted that extracellular matrix (ECM) stiffening reduced microvessel area, which was accompanied by physical uncoupling of endothelial cell (ECs) and pericytes, the cells that comprise microvessels. Nintedanib, an FDA-approved drug for treating IPF, was predicted to further potentiate microvessel regression by decreasing the percentage of quiescent pericytes while increasing the percentage of pericytes undergoing pericyte-myofibroblast transition (PMT) in high ECM stiffnesses. Importantly, the model suggested that YAP/TAZ inhibition may overcome the deleterious effects of nintedanib by promoting EC-pericyte coupling and maintaining microvessel homeostasis. Overall, our combination of computational and experimental modeling can explain how cell decisions affect tissue changes during disease and in response to treatments.

A critical evaluation of "leakage" at the cochlear blood-stria-barrier and its functional significance

The blood-labyrinth-barrier (BLB) is a semipermeable boundary between the vasculature and three separate fluid spaces of the inner ear, the perilymph, the endolymph and the intrastrial space. An important component of the BLB is the blood-stria-barrier, which shepherds the passage of ions and metabolites from strial capillaries into the intrastrial space. Some investigators have reported increased "leakage" from these capillaries following certain experimental interventions, or in the presence of inflammation or genetic variants. This leakage is generally thought to be harmful to cochlear function, principally by lowering the endocochlear potential (EP). Here, we examine evidence for this dogma. We find that strial capillaries are not exclusive, and that the asserted detrimental influence of strial capillary leakage is often confounded by hair cell damage or intrinsic dysfunction of the stria. The vast majority of previous reports speculate about the influence of strial vascular barrier function on the EP without directly measuring the EP. We argue that strial capillary leakage is common across conditions and species, and does not significantly impact the EP or hearing thresholds, either on evidentiary or theoretical grounds. Instead, strial capillary endothelial cells and pericytes are dynamic and allow permeability of varying degrees in response to specific conditions. We present observations from mice and demonstrate that the mechanisms of strial capillary transport are heterogeneous and inconsistent among inbred strains.

PGC-1α affects cochlear pericytes migration in noise-exposed mice

OBJECTIVE

The study aimed to observe the effects of noise exposure on the pericytes of the cochlear stria vascularis (SV) in mice and to investigate its molecular mechanism.

METHOD

Male C57BL/6J mice aged 6-8 weeks were used as the subjects. Auditory Brainstem Response (ABR) was used to assess hearing loss. Hematoxylin and Eosin (HE) staining was conducted to observe morphological alterations in the SV. Immunofluorescence combined with transmission electron microscopy (TEM) was used to scrutinize changes in pericytes following acoustic injury. Western blotting (WB) was used to assess the expression variations of the migration-related protein Osteopontin (OPN). Evans Blue assay was performed to evaluate the permeability of the blood labyrinth barrier (BLB). 4-Hydroxynonenal (4-HNE) staining, in conjunction with measurements of Superoxide Dismutase (SOD), Malondialdehyde (MDA), and Catalase (CAT) content, was used to ascertain whether oxidative stress injury occurred in the SV. WB, combined with immunofluorescence, was used to examine alterations in the expression of proliferator-activated receptor-gamma coactivator 1α (PGC-1α) in the SV and pericytes.

RESULTS

Noise exposure resulted in permanent hearing loss in C57BL/6J mice, accompanied by SV swelling, migration of pericytes from their vascular attachments, BLB leakage, elevated oxidative stress levels in the SV, and reduced expression of PGC-1α on both the SV and migrating pericytes.

CONCLUSION

Noise exposure may potentially increase oxidative stress levels in the SV, downregulate the expression levels of PGC-1α, promote pericytes migration, and subsequently lead to an elevation in BLB permeability.

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

VEGFA165 gene therapy ameliorates blood-labyrinth barrier breakdown and hearing loss

Millions of people are affected by hearing loss. Hearing loss is frequently caused by noise or aging and often associated with loss of pericytes. Pericytes populate the small vessels in the adult cochlea. However, their role in different types of hearing loss is largely unknown. Using an inducible and conditional pericyte depletion mouse model and noise-exposed mouse model, we show that loss of pericytes leads to marked changes in vascular structure, in turn leading to vascular degeneration and hearing loss. In vitro, using advanced tissue explants from pericyte fluorescence reporter models combined with exogenous donor pericytes, we show that pericytes, signaled by VEGF isoform A165 (VEGFA165), vigorously drive new vessel growth in both adult and neonatal mouse inner ear tissue. In vivo, the delivery of an adeno-associated virus serotype 1-mediated (AAV1-mediated) VEGFA165 viral vector to pericyte-depleted or noise-exposed animals prevented and regenerated lost pericytes, improved blood supply, and attenuated hearing loss. These studies provide the first clear-cut evidence that pericytes are critical for vascular regeneration, vascular stability, and hearing in adults. The restoration of vascular function in the damaged cochlea, including in noise-exposed animals, suggests that VEGFA165 gene therapy could be a new strategy for ameliorating vascular associated hearing disorders.

RNA Sequencing and Pathways Analyses of Middle Ear Epithelia From Patients With Otitis Media

OBJECTIVES

Otitis media (OM) is the most common pediatric diagnosis in the United States. However, our understanding of the molecular pathogenesis of OM remains relatively poor. Investigation of molecular pathways involved in OM may improve the understanding of this disease process and elucidate novel therapeutic targets. In this study, RNA sequencing (RNA-Seq) was used to discern cellular changes associated with OME compared to healthy middle ear epithelium (MEE).

STUDY DESIGN

Ex vivo case-control translational.

METHODS

Middle ear epithelia was collected from five pediatric patients diagnosed with OME undergoing tympanostomy tube placement and five otherwise healthy pediatric patients undergoing cochlear implantation. Specimens underwent RNA-Seq and pathways analyses.

RESULTS

A total of 1,292 genes exhibited differential expression in MEE from OME patients compared to controls including genes involved in inflammation, immune response to bacterial OM pathogens, mucociliary clearance, regulation of proliferation and transformation, and auditory cell differentiation. Top networks identified in OME were organismal injury and abnormalities, cell morphology, and auditory disease. Top Ingenuity canonical pathways identified were axonal guidance signaling, which contains genes associated with auditory development and disease and nicotine degradation II and III pathways. Associated upstream regulators included β-estradiol, dexamethasone, and G-protein-coupled estrogen receptor-1 (GPER1), which are associated with otoprotection or inflammation during insult.

CONCLUSIONS

RNA-Seq demonstrates differential gene expression in MEE from patients with OME compared to healthy controls with important implications for infection susceptibility, hearing loss, and a role for tobacco exposure in the development and/or severity of OME in pediatric patients.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Pericyte mechanics and mechanobiology

Pericytes are mural cells of the microvasculature, recognized by their thin processes and protruding cell body. Pericytes wrap around endothelial cells and play a central role in regulating various endothelial functions, including angiogenesis and inflammation. They also serve as a vascular support and regulate blood flow by contraction. Prior reviews have examined pericyte biological functions and biochemical signaling pathways. In this Review, we focus on the role of mechanics and mechanobiology in regulating pericyte function. After an overview of the morphology and structure of pericytes, we describe their interactions with both the basement membrane and endothelial cells. We then turn our attention to biophysical considerations, and describe contractile forces generated by pericytes, mechanical forces exerted on pericytes, and pericyte responses to these forces. Finally, we discuss 2D and 3D engineered in vitro models for studying pericyte mechano-responsiveness and underscore the need for more evolved models that provide improved understanding of pericyte function and dysfunction.

Pericyte Bridges in Homeostasis and Hyperglycemia

Diabetic retinopathy is a potentially blinding eye disease that threatens the vision of one-ninth of patients with diabetes. Progression of the disease has long been attributed to an initial dropout of pericytes that enwrap the retinal microvasculature. Revealed through retinal vascular digests, a subsequent increase in basement membrane bridges was also observed. Using cell-specific markers, we demonstrate that pericytes rather than endothelial cells colocalize with these bridges. We show that the density of bridges transiently increases with elevation of Ang-2, PDGF-BB, and blood glucose; is rapidly reversed on a timescale of days; and is often associated with a pericyte cell body located off vessel. Cell-specific knockout of KLF4 in pericytes fully replicates this phenotype. In vivo imaging of limbal vessels demonstrates pericyte migration off vessel, with rapid pericyte filopodial-like process formation between adjacent vessels. Accounting for off-vessel and on-vessel pericytes, we observed no pericyte loss relative to nondiabetic control retina. These findings reveal the possibility that pericyte perturbations in location and process formation may play a role in the development of pathological vascular remodeling in diabetic retinopathy.

Pericyte abnormalities precede strial capillary basement membrane thickening in Alport mice

In 129 Sv autosomal Alport mice, the strial capillary basement membranes (SCBMs) progressively thicken between 5 and 9 weeks of age resulting in a hypoxic microenvironment with metabolic stress and induction of pro-inflammatory cytokines and chemokines. These events occur concomitant with a drop in endocochlear potential and a susceptibility to noise-induced hearing loss under conditions that do not permanently affect age/strain-matched littermates. Here we aimed to gain an understanding of events that occur before the onset of SCBM thickening. Alport stria has normal thickness and shows levels of extracellular matrix (ECM) molecules in the SCBMs commensurate with wild-type mice. Hearing thresholds in the 3-week Alport mice do not differ from those of wild-type mice. We performed RNAseq analysis using RNA from stria vascularis isolated from 3-week Alport mice and wild type littermates. Data was processed using Ingenuity Pathway Analysis software and further distilled using manual procedures. RNAseq analysis revealed significant dysregulation of genes involved in cell adhesion, cell migration, formation of protrusions, and both actin and tubulin cytoskeletal dynamics. Overall, the data suggested changes in the cellular architecture of the stria might be apparent. To test this notion, we performed dual immunofluorescence analysis on whole mounts of the stria vascularis from these same animals stained with anti-isolectin gs-ib4 (endothelial cell marker) and anti-desmin (pericyte marker) antibodies. The results showed evidence of pericyte detachment and migration as well as the formation of membrane ruffling on pericytes in z-stacked confocal images from Alport mice compared to wild type littermates. This was confirmed by TEM analysis. Earlier work from our lab showed that endothelin A receptor blockade prevents SCBM thickening and ECM accumulation in the SCBMs. Treating cultured pericytes with endothelin-1 induced actin cytoskeletal rearrangement, increasing the ratio of filamentous to globular actin. Collectively, these findings suggest that the change in type IV collagen composition in the Alport SCBMs results in cellular insult to the pericyte compartment, activating detachment and altered cytoskeletal dynamics. These events precede SCBM thickening and hearing loss in Alport mice, and thus constitute the earliest event so far recognized in Alport strial pathology.

Activated FGF2 signaling pathway in tumor vasculature is essential for acquired resistance to anti-VEGF therapy

Anti-vascular endothelial growth factor (VEGF) therapy shows antitumor activity against various types of solid cancers. Several resistance mechanisms against anti-VEGF therapy have been elucidated; however, little is known about the mechanisms by which the acquired resistance arises. Here, we developed new anti-VEGF therapy-resistant models driven by chronic expression of the mouse VEGFR2 extracellular domain fused with the human IgG4 fragment crystallizable (Fc) region (VEGFR2-Fc). In the VEGFR2-Fc-expressing resistant tumors, we demonstrated that the FGFR2 signaling pathway was activated, and pericytes expressing high levels of FGF2 were co-localized with endothelial cells. Lenvatinib, a multiple tyrosine kinase inhibitor including VEGFR and FGFR inhibition, showed marked antitumor activity against VEGFR2-Fc-expressing resistant tumors accompanied with a decrease in the area of tumor vessels and suppression of phospho-FGFR2 in tumors. Our findings reveal the key role that intercellular FGF2 signaling between pericytes and endothelial cells plays in maintaining the tumor vasculature in anti-VEGF therapy-resistant tumors.