Dissection of Thrombospondin-4 Domains Involved in Intracellular Adaptive Endoplasmic Reticulum Stress-Responsive Signaling

zDHHC9 Regulates Cardiomyocyte Rab3a Activity and Atrial Natriuretic Peptide Secretion Through Palmitoylation of Rab3gap1

Production and release of natriuretic peptides by the stressed heart reduce cardiac workload by promoting vasodilation, natriuresis, and diuresis, which has been leveraged in the recent development of novel heart-failure pharmacotherapies, yet the mechanisms regulating cardiomyocyte exocytosis and natriuretic peptide release remain ill defined. We found that the Golgi S-acyltransferase zDHHC9 palmitoylates Rab3gap1 resulting in its spatial segregation from Rab3a, elevation of Rab3a-GTP levels, formation of Rab3a-positive peripheral vesicles, and impairment of exocytosis that limits atrial natriuretic peptide release. This novel pathway potentially can be exploited for targeting natriuretic peptide signaling in the treatment of heart failure.

Ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic membrane scaffolding of voltage-gated sodium channel NaV1.2 in neurons

Neuronal ankyrin-B is an intracellular scaffolding protein that plays multiple roles in the axon. By contrast, relatively little is known about the function of ankyrin-B in dendrites, where ankyrin-B is also localized in mature neurons. Recently, we showed that ankyrin-B acts as a scaffold for the voltage-gated sodium channel, NaV1.2, in dendrites of neocortical pyramidal neurons. How ankyrin-B is itself targeted to the dendritic membrane is not well understood. Here, we report that ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic localization of NaV1.2. We identify the palmitoyl acyl transferase zDHHC17 as a key mediator of ankyrin-B palmitoylation in heterologous cells and in neurons. Additionally, we find that zDHHC17 regulates ankyrin-B protein levels independently of its S-acylation function through a conserved binding mechanism between the ANK repeat domain of zDHHC17 and the zDHHC ankyrin-repeat binding motif of ankyrin-B. We subsequently identify five cysteines in the N-terminal ankyrin repeat domain of ankyrin-B that are necessary for ankyrin-B palmitoylation. Mutation of these five cysteines to alanines not only abolishes ankyrin-B palmitoylation, but also prevents ankyrin-B from scaffolding NaV1.2 at dendritic membranes of neurons due to ankyrin-B's inability to localize properly at dendrites. Thus, we show palmitoylation is critical for localization and function of ankyrin-B at dendrites. Strikingly, loss of ankyrin-B palmitoylation does not affect ankyrin-B-mediated axonal cargo transport of synaptic vesicle synaptotagmin-1 in neurons. This is the first demonstration of S-palmitoylation of ankyrin-B as an underlying mechanism required for ankyrin-B localization and function in scaffolding NaV1.2 at dendrites.

A role for Collagen VII in matrix protein secretion

Lack of type VII collagen (C7) disrupts cellular proteostasis yet the mechanism remains undescribed. By studying the relationship between C7 and the extracellular matrix (ECM)-associated proteins thrombospondin-1 (TSP1), type XII collagen (C12) and tissue transglutaminase (TGM2) in primary human dermal fibroblasts from multiple donors with or without the genetic disease recessive dystrophic epidermolysis bullosa (RDEB) (n=31), we demonstrate that secretion of each of these proteins is increased in the presence of C7. In dermal fibroblasts isolated from patients with RDEB, where C7 is absent or defective, association with the COPII outer coat protein SEC31 and ultimately secretion of each of these ECM-associated proteins is reduced and intracellular levels are increased. In RDEB fibroblasts, overall collagen secretion (as determined by the levels of hydroxyproline in the media) is unchanged while traffic from the ER to Golgi of TSP1, C12 and TGM2 occurs in a type I collagen (C1) dependent manner. In normal fibroblasts association of TSP1, C12 and TGM2 with the ER exit site transmembrane protein Transport ANd Golgi Organization-1 (TANGO1) as determined by proximity ligation assays, requires C7. In the absence of wild-type C7, or when ECM-associated proteins are overexpressed, C1 proximity and intracellular levels increase resulting in elevated cellular stress responses and elevated TGFβ signaling. Collectively, these data demonstrate a role for C7 in loading COPII vesicle cargo and provides a mechanism for disrupted proteostasis, elevated cellular stress and increased TGFβ signaling in patients with RDEB. Furthermore, our data point to a threshold of cargo loading that can be exceeded with increased protein levels leading to pathological outcomes in otherwise normal cells.

FAK regulates cardiomyocyte mitochondrial fission and function through Drp1

Loss of the mitochondrial fission enzyme dynamin-related protein 1 (Drp1) in cardiomyocytes results in energy shortage and heart failure. We aim to understand the intracellular signal pathway and extracellular factors regulating Drp1 phosphorylation and mitochondrial morphology and function in cardiomyocytes. We found cyclic mechanical stretching induced mitochondrial fission through Drp1 and focal adhesion kinase (FAK) in neonatal rat ventricular myocytes (NRVMs). FAK regulated phosphorylation of Drp1 and mitochondrial Drp1 levels. Extracellular fibronectin activated Drp1 and caused mitochondrial fission through FAK and extracellular signal-regulated kinase 1/2 (ERK1/2). Fibronectin increased NRVMs oxygen consumption rate and ATP content via FAK-ERK1/2-Drp1. Inhibition of the FAK-ERK1/2-Drp1 pathway caused cellular energy shortage. In addition, the FAK-ERK1/2-Drp1 pathway was rapidly activated by adrenergic agonists and contributed to agonists-stimulated NRVMs respiration. Interestingly, fibronectin limited the adrenergic agonists-induced NRVMs respiration by restricting phosphorylation of Drp1. Our results suggest that extracellular fibronectin and adrenergic stimulations use the FAK-ERK1/2-Drp1 pathway to regulate mitochondrial morphology and function in cardiomyocytes.

In the balance: how do thrombospondins contribute to the cellular pathophysiology of cardiovascular disease?

Thrombospondins (TSPs) are multidomain, secreted proteins that associate with cell surfaces and extracellular matrix. In mammals, there is a large body of data on functional roles of various TSP family members in cardiovascular disease (CVD), including stroke, cardiac remodeling and fibrosis, atherosclerosis, and aortic aneurysms. Coding single nucleotide polymorphisms (SNPs) of TSP1 or TSP4 are also associated with increased risk of several forms of CVD. Whereas interactions and functional effects of TSPs on a variety of cell types have been studied extensively, the molecular and cellular basis for the differential effects of the SNPs remains under investigation. Here, we provide an integrative review on TSPs, their roles in CVD and cardiovascular cell physiology, and known properties and mechanisms of TSP SNPs relevant to CVD. In considering recent expansions to knowledge of the fundamental cellular roles and mechanisms of TSPs, as well as the effects of wild-type and variant TSPs on cells of the cardiovascular system, we aim to highlight knowledge gaps and areas for future research or of translational potential.

Thbs1 induces lethal cardiac atrophy through PERK-ATF4 regulated autophagy

The thrombospondin (Thbs) family of secreted matricellular proteins are stress- and injury-induced mediators of cellular attachment dynamics and extracellular matrix protein production. Here we show that Thbs1, but not Thbs2, Thbs3 or Thbs4, induces lethal cardiac atrophy when overexpressed. Mechanistically, Thbs1 binds and activates the endoplasmic reticulum stress effector PERK, inducing its downstream transcription factor ATF4 and causing lethal autophagy-mediated cardiac atrophy. Antithetically, Thbs1-/- mice develop greater cardiac hypertrophy with pressure overload stimulation and show reduced fasting-induced atrophy. Deletion of Thbs1 effectors/receptors, including ATF6α, CD36 or CD47 does not diminish Thbs1-dependent cardiac atrophy. However, deletion of the gene encoding PERK in Thbs1 transgenic mice blunts the induction of ATF4 and autophagy, and largely corrects the lethal cardiac atrophy. Finally, overexpression of PERK or ATF4 using AAV9 gene-transfer similarly promotes cardiac atrophy and lethality. Hence, we identified Thbs1-mediated PERK-eIF2α-ATF4-induced autophagy as a critical regulator of cardiomyocyte size in the stressed heart.

Defining the Adult Neural Stem Cell Niche Proteome Identifies Key Regulators of Adult Neurogenesis

The mammalian brain contains few niches for neural stem cells (NSCs) capable of generating new neurons, whereas other regions are primarily gliogenic. Here we leverage the spatial separation of the sub-ependymal zone NSC niche and the olfactory bulb, the region to which newly generated neurons from the sub-ependymal zone migrate and integrate, and present a comprehensive proteomic characterization of these regions in comparison to the cerebral cortex, which is not conducive to neurogenesis and integration of new neurons. We find differing compositions of regulatory extracellular matrix (ECM) components in the neurogenic niche. We further show that quiescent NSCs are the main source of their local ECM, including the multi-functional enzyme transglutaminase 2, which we show is crucial for neurogenesis. Atomic force microscopy corroborated indications from the proteomic analyses that neurogenic niches are significantly stiffer than non-neurogenic parenchyma. Together these findings provide a powerful resource for unraveling unique compositions of neurogenic niches.

Effects of thrombospondin-4 on pro-inflammatory phenotype differentiation and apoptosis in macrophages

Thrombospondin-4 (TSP-4) attracted renewed attention recently as a result of assignment of new functions to this matricellular protein in cardiovascular, muscular, and nervous systems. We have previously reported that TSP-4 promotes local vascular inflammation in a mouse atherosclerosis model. A common variant of TSP-4, P387-TSP-4, was associated with increased cardiovascular disease risk in human population studies. In a mouse atherosclerosis model, TSP-4 had profound effect on accumulation of macrophages in lesions, which prompted us to examine its effects on macrophages in more detail. We examined the effects of A387-TSP-4 and P387-TSP-4 on mouse macrophages in cell culture and in vivo in the model of LPS-induced peritonitis. In tissues and in cell culture, TSP-4 expression was associated with inflammation: TSP-4 expression was upregulated in peritoneal tissues in LPS-induced peritonitis, and pro-inflammatory signals, INFγ, GM-CSF, and LPS, induced TSP-4 expression in macrophages in vivo and in cell culture. Deficiency in TSP-4 in macrophages from Thbs4^−/− mice reduced the expression of pro-inflammatory macrophage markers, suggesting that TSP-4 facilitates macrophage differentiation into a pro-inflammatory phenotype. Expression of TSP-4, especially more active P387-TSP-4, was associated with higher cellular apoptosis. Cultured macrophages displayed increased adhesion to TSP-4 and reduced migration in presence of TSP-4, and these responses were further increased with P387 variant. We concluded that TSP-4 expression in macrophages increases their accumulation in tissues during the acute inflammatory process and supports macrophage differentiation into a pro-inflammatory phenotype. In a model of acute inflammation, TSP-4 supports pro-inflammatory macrophage apoptosis, a response that is closely related to their pro-inflammatory activity and release of pro-inflammatory signals. P387-TSP-4 was found to be the more active form of TSP-4 in all examined functions.

Disruption of valosin-containing protein activity causes cardiomyopathy and reveals pleiotropic functions in cardiac homeostasis

Valosin-containing protein (VCP), also known as p97, is an ATPase with diverse cellular functions, although the most highly characterized is targeting of misfolded or aggregated proteins to degradation pathways, including the endoplasmic reticulum-associated degradation (ERAD) pathway. However, how VCP functions in the heart has not been carefully examined despite the fact that human mutations in VCP cause Paget disease of bone and frontotemporal dementia, an autosomal dominant multisystem proteinopathy that includes disease in the heart, skeletal muscle, brain, and bone. Here we generated heart-specific transgenic mice overexpressing WT VCP or a VCP^K524A mutant with deficient ATPase activity. Transgenic mice overexpressing WT VCP exhibit normal cardiac structure and function, whereas mutant VCP-overexpressing mice develop cardiomyopathy. Mechanistically, mutant VCP-overexpressing hearts up-regulate ERAD complex components and have elevated levels of ubiquitinated proteins prior to manifestation of cardiomyopathy, suggesting dysregulation of ERAD and inefficient clearance of proteins targeted for proteasomal degradation. The hearts of mutant VCP transgenic mice also exhibit profound defects in cardiomyocyte nuclear morphology with increased nuclear envelope proteins and nuclear lamins. Proteomics revealed overwhelming interactions of endogenous VCP with ribosomal, ribosome-associated, and RNA-binding proteins in the heart, and impairment of cardiac VCP activity resulted in aggregation of large ribosomal subunit proteins. These data identify multifactorial functions and diverse mechanisms whereby VCP regulates cardiomyocyte protein and RNA quality control that are critical for cardiac homeostasis, suggesting how human VCP mutations negatively affect the heart.

Cardiac Muscle Membrane Stabilization in Myocardial Reperfusion Injury

The phospholipid bilayer membrane that surrounds each cell in the body represents the first and last line of defense for preserving overall cell viability. In several forms of cardiac and skeletal muscle disease, deficits in the integrity of the muscle membrane play a central role in disease pathogenesis. In Duchenne muscular dystrophy, an inherited and uniformly fatal disease of progressive muscle deterioration, muscle membrane instability is the primary cause of disease, including significant heart disease, for which there is no cure or highly effective treatment. Further, in multiple clinical forms of myocardial ischemia-reperfusion injury, the cardiac sarcolemma is damaged and this plays a key role in disease etiology. In this review, cardiac muscle membrane stability is addressed, with a focus on synthetic block copolymers as a unique chemical-based approach to stabilize damaged muscle membranes. Recent advances using clinically relevant small and large animal models of heart disease are discussed. In addition, mechanistic insights into the copolymer-muscle membrane interface, featuring atomistic, molecular, and physiological structure-function approaches are highlighted. Collectively, muscle membrane instability contributes significantly to morbidity and mortality in prominent acquired and inherited heart diseases. In this context, chemical-based muscle membrane stabilizers provide a novel therapeutic approach for a myriad of heart diseases wherein the integrity of the cardiac muscle membrane is at risk.

Overlapping and differential functions of ATF6α versus ATF6β in the mouse heart

Hemodynamic stress on the mammalian heart results in compensatory hypertrophy and activation of the unfolded protein response through activating transcription factor 6α (ATF6α) in cardiac myocytes, but the roles of ATF6α or the related transcription factor ATF6β in regulating this hypertrophic response are not well-understood. Here we examined the effects of loss of ATF6α or ATF6β on the cardiac response to pressure overload. Mice gene-deleted for Atf6 or Atf6b were subjected to 2 weeks of transverse aortic constriction, and each showed a significant reduction in hypertrophy with reduced expression of endoplasmic reticulum (ER) stress-associated proteins compared with controls. However, with long-term pressure overload both Atf6 and Atf6b null mice showed enhanced decompensation typified by increased heart weight, pulmonary edema and reduced function compared to control mice. Our subsequent studies using cardiac-specific transgenic mice expressing the transcriptionally active N-terminus of ATF6α or ATF6β revealed that these factors control overlapping gene expression networks that include numerous ER protein chaperones and ER associated degradation components. This work reveals previously unappreciated roles for ATF6α and ATF6β in regulating the pressure overload induced cardiac hypertrophic response and in controlling the expression of genes that condition the ER during hemodynamic stress.

Thrombospondin-3 augments injury-induced cardiomyopathy by intracellular integrin inhibition and sarcolemmal instability

Thrombospondins (Thbs) are a family of five secreted matricellular glycoproteins in vertebrates that broadly affect cell-matrix interaction. While Thbs4 is known to protect striated muscle from disease by enhancing sarcolemmal stability through increased integrin and dystroglycan attachment complexes, here we show that Thbs3 antithetically promotes sarcolemmal destabilization by reducing integrin function, augmenting disease-induced decompensation. Deletion of Thbs3 in mice enhances integrin membrane expression and membrane stability, protecting the heart from disease stimuli. Transgene-mediated overexpression of α7β1D integrin in the heart ameliorates the disease predisposing effects of Thbs3 by augmenting sarcolemmal stability. Mechanistically, we show that mutating Thbs3 to contain the conserved RGD integrin binding domain normally found in Thbs4 and Thbs5 now rescues the defective expression of integrins on the sarcolemma. Thus, Thbs proteins mediate the intracellular processing of integrin plasma membrane attachment complexes to regulate the dynamics of cellular remodeling and membrane stability.

Defective Flux of Thrombospondin-4 through the Secretory Pathway Impairs Cardiomyocyte Membrane Stability and Causes Cardiomyopathy

Thrombospondins are stress-inducible secreted glycoproteins with critical functions in tissue injury and healing. Thrombospondin-4 (Thbs4) is protective in cardiac and skeletal muscle, where it activates an adaptive endoplasmic reticulum (ER) stress response, induces expansion of the ER, and enhances sarcolemmal stability. However, it is unclear if Thbs4 has these protective functions from within the cell, from the extracellular matrix, or from the secretion process itself. In this study, we generated transgenic mice with cardiac cell-specific overexpression of a secretion-defective mutant of Thbs4 to evaluate its exclusive intracellular and secretion-dependent functions. Like wild-type Thbs4, the secretion-defective mutant upregulates the adaptive ER stress response and expands the ER and intracellular vesicles in cardiomyocytes. However, only the secretion-defective Thbs4 mutant produces cardiomyopathy with sarcolemmal weakness and rupture that is associated with reduced adhesion-forming glycoproteins in the membrane. Similarly, deletion of Thbs4 in the mdx mouse model of Duchenne muscular dystrophy enhances cardiomyocyte membrane instability and cardiomyopathy. Finally, overexpression of the secretion-defective Thbs4 mutant in Drosophila, but not wild-type Thbs4, impaired muscle function and sarcomere alignment. These results suggest that transit through the secretory pathway is required for Thbs4 to augment sarcolemmal stability, while ER stress induction and vesicular expansion mediated by Thbs4 are exclusively intracellular processes.

Thrombospondins: Purification of human platelet thrombospondin-1

Thrombospondins are a family of five secreted proteins that have diverse roles in modulating cellular function. Thrombospondins-1 and 2 were identified as matricellular proteins based on their functional roles combined with their transient appearance or accumulation in extracellular matrix at specific times during development and in response to injury or stress in mature tissues. Thrombospondin-1 is a major component of platelet α-granules, which provides a convenient source for purification of the protein. Methods are described to prepare thrombospondin-1 from human platelets in a biologically active form with minimal degradation or contamination with other platelet proteins. A nondenaturing method is described for removing bound transforming growth factor-β1.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

Thrombospondin expression in myofibers stabilizes muscle membranes

Skeletal muscle is highly sensitive to mutations in genes that participate in membrane stability and cellular attachment, which often leads to muscular dystrophy. Here we show that Thrombospondin-4 (Thbs4) regulates skeletal muscle integrity and its susceptibility to muscular dystrophy through organization of membrane attachment complexes. Loss of the Thbs4 gene causes spontaneous dystrophic changes with aging and accelerates disease in 2 mouse models of muscular dystrophy, while overexpression of mouse Thbs4 is protective and mitigates dystrophic disease. In the myofiber, Thbs4 selectively enhances vesicular trafficking of dystrophin-glycoprotein and integrin attachment complexes to stabilize the sarcolemma. In agreement, muscle-specific overexpression of Drosophila Tsp or mouse Thbs4 rescues a Drosophila model of muscular dystrophy with augmented membrane residence of βPS integrin. This functional conservation emphasizes the fundamental importance of Thbs' as regulators of cellular attachment and membrane stability and identifies Thbs4 as a potential therapeutic target for muscular dystrophy.

Reciprocal regulation of long noncoding RNAs THBS4‑003 and THBS4 control migration and invasion in prostate cancer cell lines

Increasing evidence implicates long noncoding RNAs (lncRNAs), a class of noncoding RNAs >200 nucleotides in length, in the development of cancer. However, the mechanism underlying the effects of lncRNAs in prostate cancer (PCa) remains to be elucidated. The present study aimed to investigate the role of lncRNA-THBS4-003 in the pathogensis of PCa. In the present study, a microarray containing 8,277 lncRNA probes and 32,207 mRNA probes were used to identify dysregulated mRNAs in three patients with PCa, and reverse transcription-quantitative polymerase chain reaction was used to determine the expression levels of thrombospondin 4 (THBS4) and lncRNA-THBS4-003 in 46 primary PCa and adjacent non-tumor tissue samples. The expression levels of THBS4 were determined in six samples of PCa and adjacent non-tumor tissues using Western blot analysis. The effects of forced THBS4 knockdown and lncRNA-THBS4-003 knockdown in the two PCa cell lines, DU145 and PC-3, were evaluated using cell migration and invasion assays, as well as using Western blot analysis. Of the 40,484 probes in the microarray, 354 were significantly upregulated (P<0.05; fold-change >2). The most significantly upregulated mRNA was THBS4. The expression levels of THBS4 and lncRNA-THBS4-003 in the 46 primary PCa samples was significantly higher, compared with that in the adjacent non-tumor tissue samples. Patients with Gleason scores >7 exhibited higher expression levels of lncRNA-THBS4-003, compared with patients with lower scores. Knockdown of THBS4 or lncRNA-THBS4-003 significantly reduced the migratory and invasive abilities of the PCa cells in vitro, and decreased the expression levels of p38 and matrix metal-loproteinase (MMP)-9. These findings suggested that the reciprocal regulation of lncRNA-THBS4-003 and THBS4 contributed to the pathogenesis of PCa. Therefore silencing lncRNA-THBS4-003 or THBS4 may inhibit PCa cell migration and invasion, and regulate the levels of MMP-9 through the mitogen-activated protein kinase signaling pathway.

GRP78 Interacting Partner Bag5 Responds to ER Stress and Protects Cardiomyocytes From ER Stress-Induced Apoptosis

Bag5 is a member of the BAG family of molecular chaperone regulators and is unusual in that it consists of five BAG domains, which function as modulators of chaperone activity. Bag family proteins play a key role in cellular as well as in cardiac function and their differential expression is reported in heart failure. In this study, we examined the importance of a Bag family member protein, Bag5, in cardiomyocytes during endoplasmic reticulum (ER) stress. We found that expression of Bag5 in cardiomyocytes is significantly increased with the induction of ER stress in a time dependent manner. We have taken gain-in and loss-of functional approaches to characterize Bag5 protein function in cardiomyocytes. Adenoviral mediated expression of Bag5 significantly decreased cell death as well as improved cellular viability in ER stress. Along with this, ER stress-induced CHOP protein expression is significantly decreased in cells that overexpress Bag5. Conversely, we found that siRNA-mediated knockdown of Bag5 caused cell death, increased cytotoxicity, and decreased cellular viability in cardiomyocytes. Mechanistically, we found that Bag5 protein expression is significantly increased in the ER during ER stress and that this in turn modulates GRP78 protein stability and reduces ER stress. This study suggests that Bag5 is an important regulator of ER function and so could be exploited as a tool to improve cardiomyocyte function under stress conditions. J. Cell. Biochem. 117: 1813-1821, 2016. © 2016 Wiley Periodicals, Inc.

LRRC10 is required to maintain cardiac function in response to pressure overload

We previously reported that the cardiomyocyte-specific leucine-rich repeat containing protein (LRRC)10 has critical functions in the mammalian heart. In the present study, we tested the role of LRRC10 in the response of the heart to biomechanical stress by performing transverse aortic constriction on Lrrc10-null (Lrrc10(-/-)) mice. Mild pressure overload induced severe cardiac dysfunction and ventricular dilation in Lrrc10(-/-) mice compared with control mice. In addition to dilation and cardiomyopathy, Lrrc10(-/-) mice showed a pronounced increase in heart weight with pressure overload stimulation and a more dramatic loss of cardiac ventricular performance, collectively suggesting that the absence of LRRC10 renders the heart more disease prone with greater hypertrophy and structural remodeling, although rates of cardiac fibrosis and myocyte dropout were not different from control mice. Lrrc10(-/-) cardiomyocytes also exhibited reduced contractility in response to β-adrenergic stimulation, consistent with loss of cardiac ventricular performance after pressure overload. We have previously shown that LRRC10 interacts with actin in the heart. Here, we show that His(150) of LRRC10 was required for an interaction with actin, and this interaction was reduced after pressure overload, suggesting an integral role for LRRC10 in the response of the heart to mechanical stress. Importantly, these experiments demonstrated that LRRC10 is required to maintain cardiac performance in response to pressure overload and suggest that dysregulated expression or mutation of LRRC10 may greatly sensitize human patients to more severe cardiac disease in conditions such as chronic hypertension or aortic stenosis.