Faculty Bibliography

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.

Heart failure (HF) often coexists with cancer. Beyond the known cardiotoxicity of some cancer treatments, HF itself has been associated with increased cancer incidence. The 2 conditions share common risk factors, mechanisms, and interactions that can worsen patient outcomes. The bidirectional relationship between HF and cancer presents a complex interplay of factors that are not fully understood. Recent preclinical evidence suggests that HF may promote tumor growth via the release of protumorigenic factors from the injured heart, revealing HF as a potentially protumorigenic condition. Our review discusses the biological crosstalk between HF and cancer, emphasizing the impact of HF on tumor growth, with inflammation, and modulating the immune system as central mechanisms. We further explore the clinical implications of this connection and propose future research directions. Understanding the mechanistic overlap and interactions between HF and cancer could lead to new biomarkers and therapies, addressing the growing prevalence of both conditions and enhancing approaches to diagnosis, prevention, and treatment.

Adipose tissue (AT) is a complex connective tissue with a high relative proportion of adipocytes, which are specialized cells with the ability to store lipids in large droplets. AT is found in multiple discrete depots throughout the body, where it serves as the primary repository for excess calories. In addition, AT has an important role in functions as diverse as insulation, immunity and regulation of metabolic homeostasis. The Human Cell Atlas Adipose Bionetwork was established to support the generation of single-cell atlases of human AT as well as the development of unified approaches and consensus for cell annotation. Here, we provide a first roadmap from this bionetwork, including our suggested cell annotations for humans and mice, with the aim of describing the state of the field and providing guidelines for the production, analysis, interpretation and presentation of AT single-cell data.

Cardiolipin (CL), the signature phospholipid of mitochondria, carries four fatty acids that are remodeled after de novo synthesis. In yeast, remodeling is accomplished by the joint action of Cld1, a lipase that removes a fatty acid from CL, and Taz1, a transacylase that transfers a fatty acid from another phospholipid to monolyso-CL. While taz1 homologues have been identified in all eukaryotes, cld1 homologues have remained obscure. Here we demonstrate that ABHD18, a highly conserved protein of plants, animals, and humans, is functionally homologous to Cld1. Knockdown of Abhd18 decreased the concentration of monolyso-CL in murine, Taz-knockout myoblasts. Inactivation of Abhd18 in Drosophila substantially increased the abundance of CL. Abhd18 inactivation also reversed the increase in the rate of CL degradation, as measured with ¹³C isotopes, and the accumulation of deacylated CLs, such as monolyso-CL and dilyso-CL, in TAZ-deficient flies. CL species with more than 5 double bonds were resistant to ABHD18. Our data demonstrate that ABHD18 is the elusive lipase that hydrolyzes CL in mice and flies and presumably in other organisms. Rather than removing just one fatty acid, we show that ABHD18 deacylates CL further. Thus, ABHD18 catalyzes the breakdown of CL whereas TAZ protects CL from degradation.

UNLABELLED:Dysfunction of the endolysosomal system within neurons is a prominent feature of Alzheimer's disease (AD) pathology. Multiple AD-risk factors are known to cause hyper-activity of the early-endosome small GTPase rab5, resulting in neuronal endosomal pathway disruption. APPL1, an important rab5 effector protein, is an interface between endosomal and neuronal function through a rab5-activating interaction with the BACE1-generated C-terminal fragment (βCTF or C99) of the amyloid precursor protein (APP), a pathogenic APP fragment generated within endolysosomal compartments. To better understand the role of APPL1 in the AD endosomal phenotype, we generated a transgenic mouse model over-expressing human APPL1 within neurons (Thy1-APPL1 mice). Consistent with the important endosomal regulatory role of APPL1, Thy1-APPL1 mice have enlarged neuronal early endosomes and increased synaptic endocytosis due to increased rab5 activation. We additionally demonstrate pathological consequences of APPL1 overexpression, including functional changes in hippocampal long-term potentiation (LTP) and long-term depression (LTD), as well as degeneration of the large projection cholinergic neurons of the basal forebrain and impairment of hippocampal-dependent memory. Our findings show that increased neuronal APPL1 levels lead to a cascade of pathological effects within neurons, including early endosomal alterations, synaptic dysfunction, and neurodegeneration. Multiple risk factors and molecular regulators, including APPL1 activity, are known to contribute to the endosomal dysregulation seen in the early stages of AD, and these findings further highlight the shared pathobiology and consequences to a neuron of early endosomal pathway disruption. SIGNIFICANCE STATEMENT/UNASSIGNED:Dysfunction in the endolysosomal system within neurons is a key feature of Alzheimer's disease (AD). Multiple AD risk factors lead to hyperactivity of the early-endosome GTPase rab5, disrupting neuronal pathways including the cholinergic circuits involved early in memory decline. APPL1, a crucial rab5 effector, connects endosomal and neuronal functions through its interaction with a specific amyloid precursor protein (APP) fragment generated within endosomes. To understand APPL1's role, a transgenic mouse model over-expressing human APPL1 in neurons (Thy1-APPL1 mice) was developed. These mice show enlarged early endosomes and increased synaptic endocytosis due to rab5 activation, resulting in impaired hippocampal long-term potentiation and depression, the degeneration of basal forebrain cholinergic neurons, and memory deficits, highlighting a pathological cascade mediated through APPL1 at the early endosome.

The capacity of the brain to compensate for insults during development depends on the type of cell loss, whereas the consequences of genetic mutations in the same neurons are difficult to predict. We reveal powerful compensation from outside the mouse cerebellum when the excitatory cerebellar output neurons are ablated embryonically and demonstrate that the main requirement for these neurons is for motor coordination and not basic learning and social behaviors. In contrast, loss of the homeobox transcription factors Engrailed1/2 (EN1/2) in the cerebellar excitatory lineage leads to additional deficits in adult learning and spatial working memory, despite half of the excitatory output neurons being intact. Diffusion MRI indicates increased thalamo-cortico-striatal connectivity in En1/2 mutants, showing that the remaining excitatory neurons lacking En1/2 exert adverse effects on extracerebellar circuits regulating motor learning and select non-motor behaviors. Thus, an absence of cerebellar output neurons is less disruptive than having cerebellar genetic mutations.

Modulating mechanotransduction by inhibiting yes-associated protein (YAP) in mice yields wound regeneration without scarring. However, rodents are loose-skinned and fail to recapitulate key aspects of human wound repair. We sought to elucidate the effects of YAP inhibition in red Duroc pig wounds, the most human-like model of scarring. We show that one-time treatment with verteporfin, a YAP inhibitor, immediately after wounding is sufficient to prevent scarring and to drive wound regeneration in pigs. By performing single-cell RNA sequencing (scRNA-seq) on porcine wounds in conjunction with spatial proteomic analysis, we found perturbations in fibroblast dynamics with verteporfin treatment and the presence of putative pro-regenerative/profibrotic fibroblasts enriched in regenerating/scarring pig wounds, respectively. We also identified differences in enriched myeloid cell subpopulations after treatment and linked this observation to increased elaboration of interleukin-33 (IL-33) in regenerating wounds. Finally, we validated our findings in a xenograft wound model containing human neonatal foreskin engrafted onto nude mice and used scRNA-seq of human wound cells to draw parallels with fibroblast subpopulation dynamics in porcine wounds. Collectively, our findings provide support for the clinical translation of local mechanotransduction inhibitors to prevent human skin scarring, and they clarify a YAP/IL-33 signaling axis in large animal wound regeneration.