Faculty Bibliography

BACKGROUND:are the most common cause of familial arrhythmogenic right ventricular cardiomyopathy. This study tests whether plakophilin-2 (PKP2) deficiency only in cardiomyocytes is sufficient to provoke premature aging and proinflammatory senescence in nonmyocyte, cardiac resident cells. METHODS:We studied mice with cardiomyocyte-specific, tamoxifen-activated loss of PKP2 (cardiomyocyte-specific conditional knockout of plakophilin-2) using conventional and multiplex imaging, cytokine arrays, epigenetic clocks, spatial transcriptomics, expansion and structured illumination microscopy, and correlative data analysis. We examined nonmyocytes and cardiomyocytes for premature aging and senescence. RESULTS:We observed senescence-associated heterochromatin foci in nonmyocytes, predominantly in cells positive for α-smooth muscle actin staining. Cytokines in media of nonmyocyte cells were consistent with senescence-associated secretory phenotype. Epigenetic clocks identified premature aging. Multiplex immunohistochemistry showed nonmyocyte cells in niches, intermingled with cardiomyocytes. Spatial transcriptomics showed overrepresentation of senescence-associated secretory phenotype-related transcripts, predominantly in myocyte-rich areas of the left ventricle. Senescence-associated heterochromatin foci and increased epigenetic age were not found in cardiomyocytes from cardiomyocyte-specific conditional knockout of plakophilin-2 hearts, although we observed structural features associated with premature aging. Cross-reference analysis showed correlation between the cardiomyocyte-specific conditional knockout of plakophilin-2 cardiac proteome and that of mice 5 or 6 times their chronological age, as well as transcriptional signatures of neurodegenerative diseases. CONCLUSIONS:Loss of PKP2 expression only in adult cardiac myocytes is sufficient to induce proinflammatory senescence in nonmyocytes, and overall premature cardiac aging. This is the first study to intersect cellular senescence and premature aging with desmosomal arrhythmogenic cardiomyopathies. We speculate that cell-agnostic molecular signatures, biomarkers, and pharmacology of senescence and of neurodegenerative diseases may be relevant to diagnose or treat PKP2 arrhythmogenic right ventricular cardiomyopathy.

Neuronal axons have traditionally been considered to be the primary mediators of functional connectivity among brain regions. However, the role of astrocyte-mediated communication has been largely underappreciated. Astrocytes communicate with one another through gap junctions, but the extent and specificity of this communication remain poorly understood. Astrocyte gap junctions are necessary for memory formation^1,2, synaptic plasticity^3-5, coordination of neuronal signalling⁶, and closing the visual and motor critical periods^7,8. These findings indicate that this form of communication is essential for proper central nervous system development and function. Despite the importance of astrocyte gap junctional networks, studying them has been challenging. Current methods such as slice electrophysiology disrupt network connectivity and introduce artefacts due to tissue damage. Here, we developed a vector-based approach that labels molecules as they are fluxed by astrocyte gap junctions in awake, behaving animals to overcome these limitations. We then used whole-brain tissue clearing^9,10 to image these intact, three-dimensional astrocyte networks. We show that multiple astrocyte networks traverse the mouse brain. These networks selectively connect specific regions, rather than diffusing indiscriminately, and vary in size and organization. We observe local networks that are confined to single brain regions and long-range networks that robustly interconnect multiple regions across hemispheres, often exhibiting patterns distinct from known neuronal networks. We also demonstrate that astrocyte networks undergo structural reorganization in the adult brain after sensory deprivation. These findings reveal a mode of communication between distant brain regions that is mediated by plastic networks of gap junction-coupled astrocytes.

Cerebral malaria is a major complication of Plasmodium falciparum infection that occurs upon the sequestration of infected red blood cells (iRBCs) in brain capillaries, resulting in the loss of endothelial barrier integrity, brain swelling, and frequently long-term sequelae or death. P. falciparum-iRBCs cause the disruption of human brain microvascular endothelial cell barrier integrity in vitro, mimicking the microenvironment of cerebral malaria, yet the specific mechanisms mediating this process remain unknown. Upon infection of the host RBCs, P. falciparum produces hemozoin, a crystal form of heme generated following the degradation of hemoglobin by the parasite. Here, we show that the endothelial barrier-disrupting activity is found entirely in the hemozoin fraction of P. falciparum-iRBCs. This activity is not caused by the hemozoin crystal itself, which is not able to induce barrier disruption, but by the biomolecules that are associated with it. Treatment of purified P. falciparum hemozoin with proteases inhibits the disruption of endothelial barrier integrity caused by the hemozoin, indicating an important role for proteins in the disruption of the barrier. Conversely, treatment with nucleases did not affect hemozoin barrier-disrupting activity. These results identify a key molecular mechanism in the P. falciparum-mediated brain endothelial barrier disruption during cerebral malaria and may open new avenues for the treatment of this complication.IMPORTANCEWhile several specific biomolecules have been proposed to contribute to the disruption of endothelial barrier integrity in cerebral malaria, no single Plasmodium falciparum- or host-derived factor has been definitively identified as the primary driver of this disruption. Here, we identify the brain endothelial barrier-disruptive P. falciparum-infected red blood cell (iRBC)-derived activity to be caused by biomolecules bound to hemozoin, identifying a key, novel mechanism in the pathogenesis of cerebral malaria. The finding that P. falciparum hemozoin also disrupts a pulmonary endothelial cell barrier opens the possibility that this mechanism underlies other severe malaria complications. The implication of P. falciparum-iRBC-derived proteins in this mechanism is in line with previous reports, providing a novel interpretation of these findings in the context of hemozoin-binding. This knowledge provides a new perspective in the search for specific molecules and mechanisms involved in barrier disruption, which may lead to the development of much-needed specific treatments for cerebral malaria.

Incomplete reporting of microscopy methods undermines transparency, reproducibility, and data reuse. Despite recent initiatives, comprehensive, broadly endorsed, and accessible reporting guidelines are still lacking. Here, we present a bare minimal microscopy reporting requirements checklist that integrates human- and machine-readable input to provide clear, actionable guidance for researchers, reviewers, and publishers and to advance community standards in microscopy.

BACKGROUND:Plakophilin-2 (PKP2) is a component of the desmosome. Pathogenic variants can lead to arrhythmogenic cardiomyopathy (PKP2-ACM). In PKP2-ACM patients, exercise and catecholamine surges negatively impact arrhythmia incidence and severity. OBJECTIVE:To characterize remodeling of the sympathetic input and adrenergic response in hearts of PKP2-deficient mice (PKP2cKO) subjected to endurance exercise. METHODS:transient dynamics. Separately, we evaluated distribution of sympathetic terminals in PKP2cKO trained hearts vs controls. RESULTS:Exercise led to increased abundance of sarcolemma β1-ARs in control, and decreased abundance in PKP2cKO-myocytes. OCT3 knockdown drastically reduced the response of trained PKP2cKO-myocytes to norepinephrine but not isoproterenol, indicating preserved response to native catecholamines by intracellular (dyad-associated) receptors in the setting of a reduced sarcolemma pool. In tissue, we observed reduced abundance of sympathetic terminals, and heterogeneous distribution across the myocardium. CONCLUSION/CONCLUSIONS:Endurance exercise in PKP2-deficient myocytes leads to reduced pool of functional β1-ARs in the sarcolemma and yet availability of intracellular receptors, which can activate selected (and heterogeneous) routes of intracellular signaling cascades. We speculate that remodeling of nerve terminals affects sympathetic input distribution and hence, regional modulation of excitability and conduction. These changes can facilitate cell-generated triggered activity and heterogeneity of the underlying substrate, setting the stage for life-threatening arrhythmias.

Allergic contact dermatitis (ACD) is a delayed-type IV hypersensitivity response driven by innate and adaptive immune cells. While specific immune regulations of these cell types are amply elucidated, their regulations by extracellular matrix (ECM) components and T cell mediated adaptive immunity in ACD remains unclear. Lumican and biglycan are ECM proteoglycans abundant in the dermis and lymph node, known to regulate innate immune myeloid cells, but have not been investigated in lymphoid cell regulations in ACD. By immunohistology we localized lumican and biglycan in skin biopsies of psoriatic patients. Using wild type (WT), lumican and biglycan knockout mice, we investigated CD4⁺T cell infiltration, activation and proliferation in the skin and draining lymph node (dLN) of CHS-challenged mice by immunohistochemistry and flow cytometry. We used the OT-II adoptive transfer model to test antigen specific CD4⁺T cell activation. We assessed interactions of the proteoglycans with LFA-1 on T cells by confocal microscopy. Compared to WTs, the knockouts showed severe ear inflammation, with increased CD4⁺T cells infiltration in the dermis. CHS-challenged knockout mice dLN showed increased T-bet, STAT1 and -STAT4 signaling, indicating enhanced Th1 commitment and proliferation. We found that WT lymph node fibroblastic reticular cells (FRCs) secrete lumican, biglycan and decorin, a related proteoglycan, while none are expressed by naive or activated T cells. Lumican and biglycan interact with LFA-1 on T cell surfaces, and in vitro all three proteoglycans suppress CD4⁺T cell activation. Secreted by dLN FRCs, lumican, biglycan, and possibly decorin interact with LFA-1 on CD4⁺T cells to restrict its activation and reduce dermatitis severity.

The capsule of Streptococcus pneumoniae (Spn) is highly heterogeneous based on the expression of distinct polysaccharides. Spn transformation, controlled by the Com regulon, has been predominantly studied using unencapsulated laboratory strains. However, genomic studies revealed different rates of recombination events in clinical isolates of different serotypes. As these isolates were genetically distinct beyond capsule-encoding genes, the exact relationship between transformation and capsule remains unclear. Herein, we compared the transformability of a collection of isogenic capsule-switch strains. Strains with different capsule types and amounts significantly differed in their transformation frequency, with the unencapsulated strain having a higher frequency compared to encapsulated strains. A GFP-reporter of each strain monitoring the expression of a Com regulon-controlled gene showed similar kinetics, indicating differences in transformability were due to processes downstream of competence activation. The Com pilus, induced by competence, binds and takes in the donor DNA and is the central component of the transformation apparatus. The surface exposure of Com pilus significantly differed among serotypes with highly transformable strains having more cells binding ComGC antibody. Furthermore, electron microscopy demonstrated that transformability correlated with the proportion of cells bearing a Com pilus, which was affected by both the presence of capsule and serotype. Additionally, the unencapsulated strain displayed longer pili than encapsulated strains. Examination of capsule porosity revealed that serotypes with higher transformation frequencies had more porous capsules. Together, these results indicate that the capsule interferes with the assembly of Com pilus, thereby inhibiting the natural transformation of Spn.IMPORTANCEThe capsule is a major virulence factor of Streptococcus pneumoniae (Spn), providing a physical shield and exhibiting extensive diversity across at least 100 serotypes. Although natural transformation of Spn has predominantly been characterized in unencapsulated laboratory strains, clinical encapsulated isolates also exhibit transformability and demonstrate varied recombination rates during host carriage. We utilized otherwise genetically identical capsule-switch strains to isolate the effect of capsule on transformation. We demonstrate serotype- and quantity-dependent inhibition of transformation by the capsule, mediated through hindrance with the transformation pilus assembly and function. This study challenges the paradigm that unencapsulated laboratory strains fully recapitulate natural transformation dynamics. By redefining the capsule as a multifunctional modulator of Spn biology, balancing virulence and adaptability, our findings advance our understanding of pneumococcal evolution.

Therapeutically targeting pathogenic T cells in autoimmune diseases has been challenging. Although LAG-3, an inhibitory checkpoint receptor specifically expressed on activated T cells, is known to bind to major histocompatibility complex class II (MHC class II), we demonstrate that MHC class II interaction alone is insufficient for optimal LAG-3 function. Instead, LAG-3's spatial proximity to T cell receptor (TCR) but not CD4 co-receptor, facilitated by cognate peptide-MHC class II, is crucial in mediating CD4⁺ T cell suppression. Mechanistically, LAG-3 forms condensate with TCR signaling component CD3ε through its intracellular FSAL motif, disrupting CD3ε/lymphocyte-specific protein kinase (Lck) association. To exploit LAG-3's proximity to TCR and maximize LAG-3-dependent T cell suppression, we develop an Fc-attenuated LAG-3/TCR inhibitory bispecific antibody to bypass the requirement of cognate peptide-MHC class II. This approach allows for potent suppression of both CD4⁺ and CD8⁺ T cells and effectively alleviates autoimmune symptoms in mouse models. Our findings reveal an intricate and conditional checkpoint modulatory mechanism and highlight targeting of LAG-3/TCR cis-proximity for T cell-driven autoimmune diseases lacking effective and well-tolerated immunotherapies.

The factors that install and recognize N⁶-methyladenosine (m⁶A) on RNA to regulate gene expression are well characterized, but how their spatial organization responds to physiological stress, including infection, is unclear. Here, we show that human cytomegalovirus (HCMV) infection induces accumulation of m⁶A methyltransferase subunits, including WTAP, together with nuclear m⁶A reader YTHDC1, into distinctive, membraneless nuclear bodies (NBs) overlapping with incoming virus genomes and immediate-early (IE) RNA transcripts. De novo assembly and integrity of these DNA-associated, IE, virus-activated NBs requires RNAPII transcription, METTL3 m⁶A methyltransferase activity, and m⁶A recognition by YTHDC1, but not new protein synthesis. Depleting YTHDC1 or WTAP limits the accumulation of critical HCMV RNAs required for virus DNA replication, interfering with virus reproduction. This reveals a surprising strategy whereby a discrete sub-nuclear RNA biogenesis compartment replete with RNAPII and m⁶A modification components is swiftly consolidated in proximity to infecting HCMV genomes to initialize and sustain virus gene expression.

Embryonic development in many species, including case reports in humans, can be temporarily halted before implantation during a process called diapause. Facultative diapause occurs under conditions of maternal metabolic stress such as nursing. While molecular mechanisms of diapause have been studied, a natural inducing factor has yet to be identified. Here, we show that oxytocin induces embryonic diapause in mice. We show that gestational delays were triggered during nursing or optogenetic stimulation of oxytocin neurons simulating nursing patterns. Mouse blastocysts express oxytocin receptors, and oxytocin induced delayed implantation-like dispersion in cultured embryos. Last, oxytocin receptor-knockout embryos transferred into wild-type surrogates had low survival rates during diapause. Our results indicate that oxytocin coordinates timing of embryonic development with uterine progression through pregnancy, providing an evolutionarily conserved mechanism for ensuring successful reproduction.