Increased expression of LAP2ß eliminates nuclear membrane ruptures in nuclear lamin-deficient neurons and fibroblasts.

Defects or deficiencies in nuclear lamins cause pathology in many cell types, and recent studies have implicated nuclear membrane (NM) ruptures as a cause of cell toxicity. We previously observed NM ruptures and progressive cell death in the developing brain of lamin B1-deficient mouse embryos. We also observed frequent NM ruptures and DNA damage in nuclear lamin-deficient fibroblasts. Factors modulating susceptibility to NM ruptures remain unclear, but we noted low levels of LAP2ß, a chromatin-binding inner NM protein, in fibroblasts with NM ruptures. Here, we explored the apparent link between LAP2ß and NM ruptures in nuclear lamin-deficient neurons and fibroblasts, and we tested whether manipulating LAP2ß expression levels would alter NM rupture frequency. In cortical plate neurons of lamin B1-deficient embryos, we observed a strong correlation between low LAP2ß levels and NM ruptures. We also found low LAP2ß levels and frequent NM ruptures in neurons of cultured Lmnb1-/- neurospheres. Reducing LAP2ß expression in Lmnb1-/- neurons with an siRNA markedly increased the NM rupture frequency (without affecting NM rupture duration), whereas increased LAP2ß expression eliminated NM ruptures and reduced DNA damage. Consistent findings were observed in nuclear lamin-deficient fibroblasts. Reduced LAP2ß expression increased NM ruptures, whereas increased LAP2ß expression virtually abolished NM ruptures. Increased LAP2ß expression nearly abolished NM ruptures in cells subjected to mechanical stress (an intervention that increases NM ruptures). Our studies showed that increasing LAP2ß expression bolsters NM integrity in nuclear lamin-deficient cells and markedly reduces NM rupture frequency.

Effect of sequential burr passes on minimally invasive akin and first metatarsal dorsiflexion osteotomies.

BACKGROUND: Minimally invasive surgical (MIS) osteotomies are increasing as a surgical option for treating midfoot and forefoot conditions. This study aimed to evaluate the impact of each burr pass on the degree of correction, gap size, and alignment in MIS Akin and first metatarsal dorsiflexion osteotomies (DFO). METHODS: MIS Akin and first metatarsal DFO were performed on ten cadaveric specimens. Fluoroscopic measurements included the metatarsal dorsiflexion angle (MDA), dorsal cortical length (MDCL), first phalangeal medial cortical length (PCML) and proximal to distal phalangeal articular angle (PDPAA). RESULTS: The average decrease in PCML with each burr pass was as follows: 1.53, 1.33, 1.27, 1.23 and 1.13 mm at the 1st to 5th pass, respectively. The MDCL sequentially decreased by 1.80, 1.59, 1.35, 0.75, and 0.60 mm. The MDA consistently decreased, and the PDPAA incrementally became more valgus oriented. CONCLUSION: On average, a first metatarsal dorsal wedge resection of 4.7 mm and first phalangeal medial wedge resection of 2.9 mm was achieved after 3 and 2 burr passes, respectively. This data may aid surgeons determine the optimal number of burr passes required to achieve the desired patient-specific surgical correction.

Linking skeletal muscle aging with osteoporosis by lamin A/C deficiency.

The nuclear lamina protein lamin A/C is a key component of the nuclear envelope. Mutations in the lamin A/C gene (LMNA) are identified in patients with various types of laminopathy-containing diseases, which have features of accelerated aging and osteoporosis. However, the underlying mechanisms for laminopathy-associated osteoporosis remain largely unclear. Here, we provide evidence that loss of lamin A/C in skeletal muscles, but not osteoblast (OB)-lineage cells, results in not only muscle aging-like deficit but also trabecular bone loss, a feature of osteoporosis. The latter is due in large part to elevated bone resorption. Further cellular studies show an increase of osteoclast (OC) differentiation in cocultures of bone marrow macrophages/monocytes (BMMs) and OBs after treatment with the conditioned medium (CM) from lamin A/C-deficient muscle cells. Antibody array screening analysis of the CM proteins identifies interleukin (IL)-6, whose expression is markedly increased in lamin A/C-deficient muscles. Inhibition of IL-6 by its blocking antibody in BMM-OB cocultures diminishes the increase of osteoclastogenesis. Knockout (KO) of IL-6 in muscle lamin A/C-KO mice diminishes the deficits in trabecular bone mass but not muscle. Further mechanistic studies reveal an elevation of cellular senescence marked by senescence-associated beta-galactosidase (SA-ß-gal), p16Ink4a, and p53 in lamin A/C-deficient muscles and C2C12 muscle cells, and the p16Ink4a may induce senescence-associated secretory phenotype (SASP) and IL-6 expression. Taken together, these results suggest a critical role for skeletal muscle lamin A/C to prevent cellular senescence, IL-6 expression, hyperosteoclastogenesis, and trabecular bone loss, uncovering a pathological mechanism underlying the link between muscle aging/senescence and osteoporosis.

Everolimus rescues multiple cellular defects in laminopathy-patient fibroblasts.

LMNA encodes the A-type lamins that are part of the nuclear scaffold. Mutations in LMNA can cause a variety of disorders called laminopathies, including Hutchinson-Gilford progeria syndrome (HGPS), atypical Werner syndrome, and Emery-Dreifuss muscular dystrophy. Previous work has shown that treatment of HGPS cells with the mTOR inhibitor rapamycin or with the rapamycin analog everolimus corrects several of the phenotypes seen at the cellular level-at least in part by increasing autophagy and reducing the amount of progerin, the toxic form of lamin A that is overproduced in HGPS patients. Since other laminopathies also result in production of abnormal and potentially toxic lamin proteins, we hypothesized that everolimus would also be beneficial in those disorders. To test this, we applied everolimus to fibroblast cell lines from six laminopathy patients, each with a different mutation in LMNA Everolimus treatment increased proliferative ability and delayed senescence in all cell lines. In several cell lines, we observed that with treatment, there is a significant improvement in nuclear blebbing, which is a cellular hallmark of HGPS and other lamin disorders. These preclinical results suggest that everolimus might have clinical benefit for multiple laminopathy syndromes.

Suppression of Activated FOXO Transcription Factors in the Heart Prolongs Survival in a Mouse Model of Laminopathies.

RATIONALE: Mutations in the LMNA gene, encoding nuclear inner membrane protein lamin A/C, cause distinct phenotypes, collectively referred to as laminopathies. Heart failure, conduction defects, and arrhythmias are the common causes of death in laminopathies. OBJECTIVE: The objective of this study was to identify and therapeutically target the responsible mechanism(s) for cardiac phenotype in laminopathies. METHODS AND RESULTS: Whole-heart RNA sequencing was performed before the onset of cardiac dysfunction in the Lmna-/- and matched control mice. Differentially expressed transcripts and their upstream regulators were identified, validated, and targeted by adeno-associated virus serotype 9-short hairpin RNA constructs. A total of 576 transcripts were upregulated and 233 were downregulated in the Lmna-/- mouse hearts (q<0.05). Forkhead box O (FOXO) transcription factors (TFs) were the most activated while E2 factors were the most suppressed transcriptional regulators. Transcript levels of FOXO targets were also upregulated in the isolated Lmna-/- cardiac myocytes and in the myocardium of human heart failure patients. Nuclear localization of FOXO1 and 3 was increased, whereas phosphorylated (inactive) FOXO1 and 3 levels were reduced in the Lmna-/- hearts. Gene set enrichment analysis and gene ontology showed activation of apoptosis and inflammation and suppression of cell cycle, adipogenesis, and oxidative phosphorylation in the Lmna-/- hearts. Adeno-associated virus serotype 9-short hairpin RNA-mediated suppression of FOXO TFs rescued selected molecular signatures, improved apoptosis, and prolonged survival by ≈2-fold. CONCLUSIONS: FOXO TFs are activated and contribute to the pathogenesis of cardiac phenotype in laminopathies. Suppression of the FOXO TFs in cardiac myocytes partially rescues the phenotype and prolongs survival. The findings identify FOXO TFs as potential therapeutic targets for cardiac phenotype in laminopathies.

Lamin A/C deficiency in CD4+ T-cells enhances regulatory T-cells and prevents inflammatory bowel disease.

The mechanisms by which lamin A/C in CD4+ T-cells control intestinal homeostasis and can cause inflammatory bowel disease (IBD) are unknown. Here, we explore lamin A/C in a mouse model of IBD. Adoptive transfer to Rag1-/- mice of Lmna-/- CD4+ T-cells, which have enhanced regulatory T-cells (Treg) differentiation and function, induced less severe IBD than wild-type T-cells. Lamin A/C deficiency in CD4+ T-cells enhanced transcription of the Treg master regulator FOXP3, thus promoting Treg differentiation, and reduced Th1 polarization, due to epigenetic changes in the Th1 master regulator T-bet. In mesenteric lymph nodes, retinoic acid (RA) released by CD103+ dendritic cells downregulated lamin A/C in CD4+ T-cells, enhancing Treg differentiation. However, non-RA-producing CD103- dendritic cells predominated in peripheral lymph nodes, facilitating lamin A/C expression in CD4+ T-cells and therefore Th1 differentiation. Our findings establish lamin A/C as a key regulator of Th differentiation in physiological conditions and show it as a potential immune-regulatory target in IBD. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Lipodystrophies-Disorders of the Fatty Tissue.

Lipodystrophies are a heterogeneous group of physiological changes characterized by a selective loss of fatty tissue. Here, no fat cells are present, either through lack of differentiation, loss of function or premature apoptosis. As a consequence, lipids can only be stored ectopically in non-adipocytes with the major health consequences as fatty liver and insulin resistance. This is a crucial difference to being slim where the fat cells are present and store lipids if needed. A simple clinical classification of lipodystrophies is based on congenital vs. acquired and generalized vs. partial disturbance of fat distribution. Complications in patients with lipodystrophy depend on the clinical manifestations. For example, in diabetes mellitus microangiopathic complications such as nephropathy, retinopathy and neuropathy may develop. In addition, due to ectopic lipid accumulation in the liver, fatty liver hepatitis may also develop, possibly with cirrhosis. The consequences of extreme hypertriglyceridemia are typically acute pancreatitis or eruptive xanthomas. The combination of severe hyperglycemia with dyslipidemia and signs of insulin resistance can lead to premature atherosclerosis with its associated complications of coronary heart disease, peripheral vascular disease and cerebrovascular changes. Overall, lipodystrophy is rare with an estimated incidence for congenital (<1/1.000.000) and acquired (1-9/100.000) forms. Due to the rarity of the syndrome and the phenotypic range of metabolic complications, only studies with limited patient numbers can be considered. Experimental animal models are therefore useful to understand the molecular mechanisms in lipodystrophy and to identify possible therapeutic approaches.

Cellular strain avoidance is mediated by a functional actin cap - observations in an Lmna-deficient cell model.

In adherent cells, the relevance of a physical mechanotransduction pathway provided by the perinuclear actin cap stress fibers has recently emerged. Here, we investigate the impact of a functional actin cap on the cellular adaptive response to topographical cues and uniaxial cyclic strain. Lmna-deficient fibroblasts are used as a model system because they do not develop an intact actin cap, but predominantly form a basal layer of actin stress fibers underneath the nucleus. We observe that topographical cues induce alignment in both normal and Lmna-deficient fibroblasts, suggesting that the topographical signal transmission occurs independently of the integrity of the actin cap. By contrast, in response to cyclic uniaxial strain, Lmna-deficient cells show a compromised strain avoidance response, which is completely abolished when topographical cues and uniaxial strain are applied along the same direction. These findings point to the importance of an intact and functional actin cap in mediating cellular strain avoidance.

Importance of early diagnosis in LMNA-related muscular dystrophy for cardiac surveillance.

INTRODUCTION: The identification of LMNA-related muscular dystrophy is important because it poses life-threatening cardiac complications. However, diagnosis of LMNA-related muscular dystrophy based on clinical features is challenging. METHODS: We reviewed the clinical phenotypes of 14 children with LMNA variants, focusing on the cardiac function and genotypes. RESULTS: Most patients presented with motor developmental delay or gait abnormalities. Eight (57%) patients had prominent neck extensor weakness or contractures. All patients showed ankle contractures at an early stage. Regular cardiac surveillance allowed for the detection of dysrhythmias in 57% of patients at a mean age of 14 years (range, 5-26). All patients had missense variants; however, there were no clear phenotype-genotype correlations. DISCUSSION: Early diagnosis of LMNA-related muscular dystrophy provides an opportunity for cardiac surveillance, potentially leading to the prevention of cardiac mortality in children.

Lamin A/C and emerin regulate MKL1-SRF activity by modulating actin dynamics.

Laminopathies, caused by mutations in the LMNA gene encoding the nuclear envelope proteins lamins A and C, represent a diverse group of diseases that include Emery-Dreifuss muscular dystrophy (EDMD), dilated cardiomyopathy (DCM), limb-girdle muscular dystrophy, and Hutchison-Gilford progeria syndrome. Most LMNA mutations affect skeletal and cardiac muscle by mechanisms that remain incompletely understood. Loss of structural function and altered interaction of mutant lamins with (tissue-specific) transcription factors have been proposed to explain the tissue-specific phenotypes. Here we report in mice that lamin-A/C-deficient (Lmna(-/-)) and Lmna(N195K/N195K) mutant cells have impaired nuclear translocation and downstream signalling of the mechanosensitive transcription factor megakaryoblastic leukaemia 1 (MKL1), a myocardin family member that is pivotal in cardiac development and function. Altered nucleo-cytoplasmic shuttling of MKL1 was caused by altered actin dynamics in Lmna(-/-) and Lmna(N195K/N195K) mutant cells. Ectopic expression of the nuclear envelope protein emerin, which is mislocalized in Lmna mutant cells and also linked to EDMD and DCM, restored MKL1 nuclear translocation and rescued actin dynamics in mutant cells. These findings present a novel mechanism that could provide insight into the disease aetiology for the cardiac phenotype in many laminopathies, whereby lamin A/C and emerin regulate gene expression through modulation of nuclear and cytoskeletal actin polymerization.

Depletion of A-type lamins and Lap2α reduces 53BP1 accumulation at UV-induced DNA lesions and Lap2α protein is responsible for compactness of irradiated chromatin.

We studied how deficiency in lamins A/C and lamina-associated polypeptide 2α (Lap2α) affects DNA repair after irradiation. A-type lamins and Lap2α were not recruited to local DNA lesions and did not accumulate to γ-irradiation-induced foci (IRIF), as it is generally observed for well-known marker of DNA lesions, 53BP1 protein. At micro-irradiated chromatin of lmna double knockout (dn) and Lap2α dn cells, 53BP1 protein levels were reduced, compared to locally irradiated wild-type counterpart. Decreased levels of 53BP1 we also observed in whole populations of lmna dn and Lap2α dn cells, irradiated by UV light. We also studied distribution pattern of 53BP1 protein in a genome outside micro-irradiated region. In Lap2α deficient cells, identical fluorescence of mCherry-tagged 53BP1 protein was found at both microirradiated region and surrounding chromatin. However, a well-known marker of double strand breaks, γH2AX, was highly abundant in the lesion-surrounding genome of Lap2α deficient cells. Described changes, induced by irradiation in Lap2α dn cells, were not accompanied by cell cycle changes. In Lap2α dn cells, we additionally performed analysis by FLIM (Fluorescence Lifetime Imaging Microscopy) that showed different dynamic behavior of mCherry-tagged 53BP1 protein pools when it was compared with wild-type (wt) fibroblasts. This analysis revealed three different fractions of mCherry-53BP1 protein. Two of them showed identical exponential decay times (τ1 and τ3), but the decay rate of τ2 and amplitudes of fluorescence decays (A1-A3) were statistically different in wt and Lap2α dn fibroblasts. Moreover, γ-irradiation weakened an interaction between A-type lamins and Lap2α. Together, our results demonstrate how depletion of Lap2α affects DNA damage response (DDR) and how chromatin compactness is changed in Lap2α deficient cells exposed to radiation.

Lamin A/C deficiency reduces circulating tumor cell resistance to fluid shear stress.

Metastasis contributes to over 90% of cancer-related deaths and is initiated when cancer cells detach from the primary tumor, invade the basement membrane, and enter the circulation as circulating tumor cells (CTCs). While metastasis is viewed as an inefficient process with most CTCs dying within the bloodstream, it is evident that some CTCs are capable of resisting hemodynamic shear forces to form secondary tumors in distant tissues. We hypothesized that nuclear lamins A and C (A/C) act as key structural components within CTCs necessary to resist destruction from elevated shear forces of the bloodstream. Herein, we show that, compared with nonmalignant epithelial cells, tumor cells are resistant to elevated fluid shear forces in vitro that mimic those within the bloodstream, as evidenced by significant decreases in cellular apoptosis and necrosis. Knockdown of lamin A/C significantly reduced tumor cell resistance to fluid shear stress, with significantly increased cell death compared with parental tumor cell and nontargeting controls. Interestingly, lamin A/C knockdown increased shear stress-induced tumor cell apoptosis, but did not significantly affect cellular necrosis. These data demonstrate that lamin A/C is an important structural component that enables tumor cell resistance to fluid shear stress-mediated death in the bloodstream, and may thus facilitate survival and hematogenous metastasis of CTCs.

Defective skeletal muscle growth in lamin A/C-deficient mice is rescued by loss of Lap2α.

Mutations in lamin A/C result in a range of tissue-specific disorders collectively called laminopathies. Of these, Emery-Dreifuss and Limb-Girdle muscular dystrophy 1B mainly affect striated muscle. A useful model for understanding both laminopathies and lamin A/C function is the Lmna(-/-) mouse. We found that skeletal muscle growth and muscle satellite (stem) cell proliferation were both reduced in Lmna(-/-) mice. Lamins A and C associate with lamina-associated polypeptide 2 alpha (Lap2α) and the retinoblastoma gene product, pRb, to regulate cell cycle exit. We found Lap2α to be upregulated in Lmna(-/-) myoblasts (MBs). To specifically test the contribution of elevated Lap2α to the phenotype of Lmna(-/-) mice, we generated Lmna(-/-)Lap2α(-/-) mice. Lifespan and body mass were increased in Lmna(-/-)Lap2α(-/-) mice compared with Lmna(-/-). Importantly, the satellite cell proliferation defect was rescued, resulting in improved myogenesis. Lmna(-/-) MBs also exhibited increased levels of Smad2/3, which were abnormally distributed in the cell and failed to respond to TGFß1 stimulation as in control cells. However, using SIS3 to inhibit signaling via Smad3 reduced cell death and augmented MB fusion. Together, our results show that perturbed Lap2α/pRb and Smad2/3 signaling are important regulatory pathways mediating defective muscle growth in Lmna(-/-) mice, and that inhibition of either pathway alone or in combination can ameliorate this deleterious phenotype.

A new pathway that regulates 53BP1 stability implicates cathepsin L and vitamin D in DNA repair.

Genomic instability due to telomere dysfunction and defective repair of DNA double-strand breaks (DSBs) is an underlying cause of ageing-related diseases. 53BP1 is a key factor in DNA DSBs repair and its deficiency is associated with genomic instability and cancer progression. Here, we uncover a novel pathway regulating the stability of 53BP1. We demonstrate an unprecedented role for the cysteine protease Cathepsin L (CTSL) in the degradation of 53BP1. Overexpression of CTSL in wild-type fibroblasts leads to decreased 53BP1 protein levels and changes in its cellular distribution, resulting in defective repair of DNA DSBs. Importantly, we show that the defects in DNA repair associated with 53BP1 deficiency upon loss of A-type lamins are due to upregulation of CTSL. Furthermore, we demonstrate that treatment with vitamin D stabilizes 53BP1 and promotes DNA DSBs repair via inhibition of CTSL, providing an as yet unsuspected link between vitamin D action and DNA repair. Given that CTSL upregulation is a hallmark of cancer and progeria, regulation of this pathway could be of great therapeutic significance for these diseases.

Loss of Drosophila A-type lamin C initially causes tendon abnormality including disintegration of cytoskeleton and nuclear lamina in muscular defects.

Lamins are the major components of nuclear envelope architecture, being required for both the structural and informational roles of the nuclei. Mutations of lamins cause a spectrum of diseases in humans, including muscular dystrophy. We report here that the loss of the A-type lamin gene, lamin C in Drosophila resulted in pupal metamorphic lethality caused by tendon defects, matching the characteristics of human A-type lamin revealed by Emery-Dreifuss muscular dystrophy (EDMD). In tendon cells lacking lamin C activity, overall cell morphology was affected and organization of the spectraplakin family cytoskeletal protein Shortstop which is prominently expressed in tendon cells gradually disintegrated, notably around the nucleus and in a manner correlating well with the degradation of musculature. Furthermore, lamin C null mutants were efficiently rescued by restoring lamin C expression to shortstop-expressing cells, which include tendon cells but exclude skeletal muscle cells. Thus the critical function of A-type lamin C proteins in Drosophila musculature is to maintain proper function and morphology of tendon cells.

Nuclear lamins, diseases and aging.

Nuclear lamins are type V intermediate filament proteins. They are the major building blocks of the peripheral nuclear lamina, a complex meshwork of proteins underlying the inner nuclear membrane. In addition to providing nuclear shape and mechanical stability, they are required for chromatin organization, transcription regulation, DNA replication, nuclear assembly and nuclear positioning. Over the past few years, interest in the lamins has increased because of the identification of at least 12 distinct human diseases associated with mutations in the LMNA gene, which encodes A-type lamins. These diseases, collectively termed laminopathies, affect muscle, adipose, bone, nerve and skin cells and range from muscular dystrophies to accelerated aging.

Trajectories and nuclear arrangement of PML bodies are influenced by A-type lamin deficiency.

BACKGROUND INFORMATION: Promyelocytic leukaemia (PML) bodies are specific nuclear structures with functional significance for acute promyelocytic leukaemia. In this study, we analysed the trajectories of PML bodies using single-particle tracking. RESULTS: We observed that the recovery of PML protein after photobleaching was ATP dependent in both wild-type (wt) and A-type lamin-deficient cells. The movement of PML bodies was faster and the nuclear area occupied by particular PML bodies was larger in A-type lamin-deficient fibroblasts compared with their wt counterparts. Moreover, dysfunction of the LMNA gene increased the frequency of mutual interactions between individual PML bodies and influenced the morphology of these domains at the ultrastructural level. As a consequence of A-type lamin deficiency, PML protein accumulated in nuclear blebs and frequently appeared at the nuclear periphery. CONCLUSIONS: We suggest that the physiological function of lamin A proteins is important for events that occur in the compartment of PML bodies. This observation was confirmed in other experimental models characterised by lamin changes, including apoptosis or the differentiation of mouse embryonic stem cells.

Nucleoplasmic LAP2alpha-lamin A complexes are required to maintain a proliferative state in human fibroblasts.

In human diploid fibroblasts (HDFs), expression of lamina-associated polypeptide 2 alpha (LAP2alpha) upon entry and exit from G(0) is tightly correlated with phosphorylation and subnuclear localization of retinoblastoma protein (Rb). Phosphoisoforms of Rb and LAP2alpha are down-regulated in G(0). Although RbS780 phosphoform and LAP2alpha are up-regulated upon reentry into G(1) and colocalize in the nucleoplasm, RbS795 migrates between nucleoplasmic and speckle compartments. In HDFs, which are null for lamins A/C, LAP2alpha is mislocalized within nuclear aggregates, and this is correlated with cell cycle arrest and accumulation of Rb within speckles. Nuclear retention of nucleoplasmic Rb during G(1) phase but not of speckle-associated Rb depends on lamin A/C. siRNA knock down of LAP2alpha or lamin A/C in HDFs leads to accumulation of Rb in speckles and G(1) arrest, probably because of activation of a cell cycle checkpoint. Our results suggest that LAP2alpha and lamin A/C are involved in controlling Rb localization and phosphorylation, and a lack or mislocalization of either protein leads to cell cycle arrest in HDFs.

Effects of mechanical stress and carvedilol in lamin A/C-deficient dilated cardiomyopathy.

RATIONALE: Mutations in the LMNA gene, which encodes the nuclear lamina proteins lamin A and lamin C, are the most common cause of familial dilated cardiomyopathy (DCM). Mechanical stress-induced apoptosis has been proposed as the mechanism underpinning DCM in lamin A/C-deficient hearts, but supporting in vivo evidence has been lacking. OBJECTIVE: Our aim was to study interventions to modify mechanical stress in heterozygous Lmna knockout (Lmna(+/-)) mice. METHODS AND RESULTS: Cardiac structure and function were evaluated before and after exercise training, thoracic aortic constriction, and carvedilol treatment. Lmna(+/-) mice develop adult-onset DCM with relatively more severe disease in males. Lmna(+/-) cardiomyocytes show altered nuclear morphology and perinuclear desmin organization, with enhanced responses to hypo-osmotic stress indicative of cytoskeletal instability. Despite these structural defects that provide a template for mechanical stress-induced damage, young Lmna(+/-) mice subjected to 6 weeks of moderate or strenuous exercise training did not show induction of apoptosis or accelerated DCM. In contrast, regular moderate exercise attenuated DCM development in male Lmna(+/-) mice. Sustained pressure overload generated by thoracic aortic constriction depressed ventricular contraction in young wild-type and Lmna(+/-) mice with no sex or genotype differences in the time-course or severity of response. Treatment of male Lmna(+/-) mice from 12 to 40 weeks with the beta-blocker, carvedilol, prevented the dilatation and contractile dysfunction that was observed in placebo-treated mice. CONCLUSIONS: These data suggest that factors other than mechanical stress-induced apoptosis contribute to DCM and provide the first demonstration that regular moderate exercise and carvedilol can modify disease progression in lamin A/C-deficient hearts.