Genetic Risk of Primary Aldosteronism and Its Contribution to Hypertension: A Cross-Ancestry Meta-Analysis of Genome-Wide Association Studies.

BACKGROUND: Hypertension imposes substantial health and economic burden worldwide. Primary aldosteronism (PA) is one of the most common causes of secondary hypertension, causing cardiovascular events at higher risk compared with essential hypertension. However, the germline genetic contribution to the susceptibility of PA has not been well elucidated. METHOD: We conducted a genome-wide association analysis of PA in the Japanese population and a cross-ancestry meta-analysis combined with UK Biobank and FinnGen cohorts (816 PA cases and 425 239 controls) to identify genetic variants that contribute to PA susceptibility. We also performed a comparative analysis for the risk of 42 previously established blood pressure-associated variants between PA and hypertension with the adjustment of blood pressure. RESULTS: In the Japanese genome-wide association study, we identified 10 loci that presented suggestive evidence for the association with the PA risk (P<1.0×10-6). In the meta-analysis, we identified 5 genome-wide significant loci (1p13, 7p15, 11p15, 12q24, and 13q12; P<5.0×10-8), including 3 of the suggested loci in the Japanese genome-wide association study. The strongest association was observed at rs3790604 (1p13), an intronic variant of WNT2B (odds ratio, 1.50 [95% CI, 1.33-1.69]; P=5.2×10-11). We further identified 1 nearly genome-wide significant locus (8q24, CYP11B2), which presented a significant association in the gene-based test (P=7.2×10-7). Of interest, all of these loci were known to be associated with blood pressure in previous studies, presumably because of the prevalence of PA among individuals with hypertension. This assumption was supported by the observation that they had a significantly higher risk effect on PA than on hypertension. We also revealed that 66.7% of the previously established blood pressure-associated variants had a higher risk effect for PA than for hypertension. CONCLUSIONS: This study demonstrates the genome-wide evidence for a genetic predisposition to PA susceptibility in the cross-ancestry cohorts and its significant contribution to the genetic background of hypertension. The strongest association with the WNT2B variants reinforces the implication of the Wnt/ß-catenin pathway in the PA pathogenesis.

Variation in plasma glucagon levels according to obesity status in Japanese Americans with normal glucose tolerance.

Japanese Americans living in the United States are genetically identical to Japanese people, but have undergone a rapid and intense westernization of their lifestyle. This study investigated variability in glucagon secretion after glucose loading among Japanese Americans with normal glucose tolerance (NGT) according to obesity status. The 75-g oral glucose tolerance test (OGTT) was performed for 138 Japanese Americans (aged 40-75 years) living in Los Angeles. Plasma glucagon levels measured using the sandwich enzyme-linked immunosorbent assay were compared according to body mass index (BMI) categories among 119 individuals with NGT. The individuals were classified into three categories according to their BMI values: <22 kg/m2 (n = 37), 22-24.9 kg/m2 (n = 46), and ≥25 kg/m2 (n = 36). Fasting plasma glucagon levels and glucagon-area under the curve levels during the OGTT were the highest in the BMI ≥25 kg/m2 group. Fasting glucagon levels were correlated with BMI (r = 0.399, p < 0.001), fasting insulin levels (r = 0.275, p = 0.003) and the homeostasis model assessment-insulin resistance (r = 0.262, p = 0.004). In conclusion, our findings suggest that fasting hyperglucagonemia is associated with obesity and insulin resistance even during the NGT stage in the Japanese American population.

ATP1A1 Mutant in Aldosterone-Producing Adenoma Leads to Cell Proliferation.

The molecular mechanisms by which ATP1A1 mutation-mediated cell proliferation or tumorigenesis in aldosterone-producing adenomas (APAs) have not been elucidated. First, we investigated whether the APA-associated ATP1A1 L104R mutation stimulated cell proliferation. Second, we aimed to clarify the molecular mechanisms by which the ATP1A1 mutation-mediated cell proliferated. We performed transcriptome analysis in APAs with ATP1A1 mutation. ATP1A1 L104R mutation were modulated in human adrenocortical carcinoma (HAC15) cells (ATP1A1-mutant cells), and we evaluated cell proliferation and molecular signaling events. Transcriptome and immunohistochemical analysis showed that Na/K-ATPase (NKA) expressions in ATP1A1 mutated APA were more abundant than those in non-functioning adrenocortical adenoma or KCNJ5 mutated APAs. The significant increase of number of cells, amount of DNA and S-phase population were shown in ATP1A1-mutant cells. Fluo-4 in ATP1A1-mutant cells were significantly increased. Low concentration of ouabain stimulated cell proliferation in ATP1A1-mutant cells. ATP1A1-mutant cells induced Src phosphorylation, and low concentration of ouabain supplementation showed further Src phosphorylation. We demonstrated that NKAs were highly expressed in ATP1A1 mutant APA, and the mutant stimulated cell proliferation and Src phosphorylation in ATP1A1-mutant cells. NKA stimulations would be a risk factor for the progression and development to an ATP1A1 mutant APA.

Collagen VI deficiency reduces muscle pathology, but does not improve muscle function, in the γ-sarcoglycan-null mouse.

Muscular dystrophy is characterized by progressive skeletal muscle weakness and dystrophic muscle exhibits degeneration and regeneration of muscle cells, inflammation and fibrosis. Skeletal muscle fibrosis is an excessive deposition of components of the extracellular matrix including an accumulation of Collagen VI. We hypothesized that a reduction of Collagen VI in a muscular dystrophy model that presents with fibrosis would result in reduced muscle pathology and improved muscle function. To test this hypothesis, we crossed γ-sarcoglycan-null mice, a model of limb-girdle muscular dystrophy type 2C, with a Col6a2-deficient mouse model. We found that the resulting γ-sarcoglycan-null/Col6a2Δex5 mice indeed exhibit reduced muscle pathology compared with γ-sarcoglycan-null mice. Specifically, fewer muscle fibers are degenerating, fiber size varies less, Evans blue dye uptake is reduced and serum creatine kinase levels are lower. Surprisingly, in spite of this reduction in muscle pathology, muscle function is not significantly improved. In fact, grip strength and maximum isometric tetanic force are even lower in γ-sarcoglycan-null/Col6a2Δex5 mice than in γ-sarcoglycan-null mice. In conclusion, our results reveal that Collagen VI-mediated fibrosis contributes to skeletal muscle pathology in γ-sarcoglycan-null mice. Importantly, however, our data also demonstrate that a reduction in skeletal muscle pathology does not necessarily lead to an improvement of skeletal muscle function, and this should be considered in future translational studies.

Particular Morphology of Inferior Pulmonary Veins and Difficulty of Cryoballoon Ablation in Patients With Paroxysmal Atrial Fibrillation.

BACKGROUND: The CRYO-Japan PMS study indicated that cryoballoon ablation (Cryo-Abl) has a lower acute success rate of pulmonary vein isolation (PVI) for the right and left inferior PVs (RIPV and LIPV, respectively) than for the superior PVs. This study aimed to determine if the orientation and position of the inferior PVs are related to the difficulty of acute success of PVI.Methods and Results:We investigated 30 consecutive patients who underwent Cryo-Abl. A "difficult PV" was defined as the requirement for >2 cooling applications and/or touch-up ablation to achieve PVI. We measured the ventral angle between the vertical line and the direction of each PV trunk (PV angle) on the transverse plane of enhanced CT images. PV position was defined as the difference in the levels between the bottom of the RIPVs and the non-coronary cusp of the aorta. PV angle <105° and PV position <1.250 mm were independent factors of difficult RIPV isolation (PV angle: odds ratio (OR)=23.80, confidence interval (CI) -3.15528 to -0.53622, P=0.002; PV position: OR=12.14, CI -2.77301 to -0.23160, P=0.014). PV position <16.875 mm was also related to the difficulty of LIPV isolation (OR=5.78, CI -1.77095 to -0.09474, P=0.027). CONCLUSIONS: RIPV with ventral orientation may require difficult maneuvers to advance an ablation system towards it. Low take-off of the inferior PVs may cause non-coaxial configuration of balloon catheters towards the direction of these veins.

A novel method to estimate blood flow velocity in the left atrial appendage using enhanced computed tomography: role of Hounsfield unit density ratio at two distinct points within the left atrial appendage.

Low blood flow velocity in the left atrial appendage (LAA) indicates a high risk of thromboembolism. Although transesophageal echocardiography (TEE) has been the standard method with which to evaluate the LAA blood flow velocity, a clinically noninvasive method is desired. We hypothesized that the ratio of the Hounsfield unit (HU) density at two distinct points within the LAA represents the blood flow velocity in the LAA. We retrospectively investigated 60 consecutive patients with atrial fibrillation (paroxysmal type, n = 29) who underwent enhanced computed tomography (CT) and TEE. The peak emptying flow velocity in the LAA (LAAPV) was evaluated using TEE. HU density was measured at proximal and distal sites of the LAA (LAAp and LAAd) on CT images. The LAAd/LAAp ratio was correlated with the LAAPV (P < 0.01, r = 0.69). Among several indices, the HU ratio was the most significant parameter associated with the LAAPV (ß = 0.469, CI 28.602-68.286, P < 0.001). Receiver-operating characteristic analysis (area under the curve, 0.91) demonstrated that an HU density ratio cutoff of 0.32 discriminated a low LAAPV (<25 cm/s) with sensitivity of 90% and specificity of 84%. Flow velocity of the LAA can be estimated by the HU density ratio at distal and proximal sites within the LAA. Our method might be a feasible substitution for TEE to discriminate patients with a reduced LAAPV.

Impact of impaired glucose tolerance on clopidogrel response in patients with coronary artery disease.

Although patients with impaired glucose tolerance (IGT) are at increased atherothrombotic risk, it is unclear how antiplatelet drugs act in patients with IGT. The aim of this study was to investigate the pharmacodynamic response to clopidogrel in patients with IGT and insulin resistance (IR). A 75 g oral glucose tolerance test was performed in 65 coronary artery disease (CAD) patients on aspirin and clopidogrel therapy. Platelet function tests were assessed at 3 time-points by light transmittance aggregometry using ADP (5 and 20 µmol/L) stimuli. 30 patients had IGT and 35 normal glucose tolerance (NGT). Among them, 13 patients showed IR. Following ADP stimuli, patients with IGT showed significantly higher maximal platelet aggregation at each time point than those with NGT patients. This resulted in greater high on-treatment platelet reactivity (HPR) rates at each time point in IGT patients (53.3-36.7 vs. 14.3-11.4 %, p < 0.05). A multivariable logistic regression analysis showed that IGT status was the strongest predictor of HPR (odds ratio 7.54, 95 % CI 1.95-29.1, p = 0.003). Following a glucose load, profiles of platelet reactivity varied according to IR status, with minimal changes over time in patients with IR, while there was a significant reduction in the non-IR patients. In aspirin and clopidogrel-treated patients with CAD, IGT is associated with enhanced platelet reactivity and increased rates of HPR compared with NGT patients. These findings suggest the presence of platelet dysfunction in patients with IGT, which may be attributed to the presence of IR.

Difference in neointimal coverage at chronic stage between bare metal stent and sirolimus-eluting stent evaluated at stent-strut level by optical coherence tomography.

Compared with the bare metal stent (BMS), suppression of neointimal growth in the sirolimus-eluting stent (SES) reduced restenosis at the cost of more exposed struts that could impose the risk of stent thrombosis. The present study was conducted to analyze neointimal coverage patterns of stents at a strut-level after implantation of BMS or SES with the use of optical coherence tomography (OCT). We enrolled 35 patients and analyzed neointimal coverage of every strut from 41 stents (BMS: n = 8, SES: n = 33) by using OCT at follow-up of the stent implantation. All of the 371 struts from eight BMSs were covered with ≥100 µm of neointima, while 19.8 and 3.5% of 3,478 struts from 33 SESs were uncovered (neointimal thickness of <10 µm) and malapposed, respectively. The histogram of neointimal thickness showed basically normal distribution in BMS but skewed in SES. No regional difference in neointimal thickness was observed in BMS (proximal, 535.7 ± 25.2 µm; body, 532.4 ± 17.0 µm; distal, 485.8 ± 27.0 µm). In SES, however, the body segment showed thinner neointima [median 40 µm (interquartile range (IQR) 10-90 µm)] than proximal [60 µm (IQR 10-140 µm), p < 0.001] or distal [50 µm (IQR 10-110 µm), p < 0.001] segment, while uncovered and malapposed struts were more frequent in the proximal and body segments. In conclusion, SES, compared with BMS, showed more suppressed neointimal growth with regional variation: neointimal thickness was the least in the body part while the ratio of exposed and malapposed struts was minimal in the distal segment. OCT was useful for a strut-level analysis of neointimal coverage over the whole stent.

Metastasis-associated protein, S100A4 mediates cardiac fibrosis potentially through the modulation of p53 in cardiac fibroblasts.

Metastasis-associated protein, S100A4 is suggested as a marker for fibrosis in several organs. It also modulates DNA binding of p53 and affects its function. However, the functional role of S100A4 in the myocardium has remained unclear. Therefore, we investigated the role of S100A4 and its relationship with p53 in cardiac fibrosis. In Dahl-rat hypertensive heart disease model, S100A4 was upregulated in the hypertrophic myocardium and further activated during transition to heart failure (HF). It was expressed in various cells including fibroblasts. In in vitro cardiac fibroblasts, the knockdown of S100A4 significantly suppressed both cell proliferation and collagen expressions. S100A4 co-localized and interacted with p53 in the nucleus. S100A4 knockdown increased the expression of p53-downstream genes, p21 and mdm2, and concomitant knockdown of p53 recovered cell proliferation and collagen expression. Transverse aortic constriction (TAC) was performed in S100A4 knockout (KO) mice, which showed a similar baseline-phenotype to wild type (WT) mice. Although there was no difference in hypertrophic response, KO mice showed reduced interstitial fibrosis, decreased myofibroblasts, and suppressed expressions of collagens and profibrotic cytokines in the left ventricle. Also, DNA microarray analysis showed that S100A4 knockout in vivo had a significant impact on expressions of p53-associated genes. These findings suggest that S100A4 modulates p53 function in fibroblasts and thereby mediates myocardial interstitial fibrosis through two distinct mechanisms; cell proliferation and collagen expression. Blockade of S100A4 may have therapeutic potential in cardiac hypertrophy and HF by attenuating cardiac fibrosis.

Selective activation of PPARα maintains thermogenic capacity of beige adipocytes.

Beige adipocytes are inducible thermogenic adipocytes used for anti-obesity treatment. Beige adipocytes rapidly lose their thermogenic capacity once external cues are removed. However, long-term administration of stimulants, such as PPARγ and ß-adrenergic receptor agonists, is unsuitable due to various side effects. Here, we reported that PPARα pharmacological activation was the preferred target for maintaining induced beige adipocytes. Pemafibrate used in clinical practice for dyslipidemia was developed as a selective PPARα modulator (SPPARMα). Pemafibrate administration regulated the thermogenic capacity of induced beige adipocytes, repressed body weight gain, and ameliorated impaired glucose tolerance in diet-induced obese mouse models. The transcriptome analysis revealed that the E-twenty-six transcription factor ELK1 acted as a cofactor of PPARα. ELK1 was mobilized to the Ucp1 transcription regulatory region with PPARα and modulated its expression by pemafibrate. These results suggest that selective activation of PPARα by pemafibrate is advantageous to maintain the function of beige adipocytes.

Association of DNA methylation with steroidogenic enzymes in Cushing's adenoma.

DNA methylation and demethylation regulate the transcription of genes. DNA methylation-associated gene expression of adrenal steroidogenic enzymes may regulate cortisol production in cortisol-producing adenoma (CPA). We aimed to determine the DNA methylation levels of all genes encoding steroidogenic enzymes involved in CPA. Additionally, the aims were to clarify the DNA methylation-associated gene expression and evaluate the difference of CPA genotype from others using DNA methylation data. Twenty-five adrenal CPA and six nonfunctioning adrenocortical adenoma (NFA) samples were analyzed. RNA sequencing and DNA methylation array were performed. The methylation levels at 118 methylation sites of the genes were investigated, and their methylation and mRNA levels were subsequently integrated. Among all the steroidogenic enzyme genes studied, CYP17A1 gene was mainly found to be hypomethylated in CPA compared to that in NFA, and the Benjamini-Hochberg procedure demonstrated that methylation levels at two sites in the CYP17A1 gene body were statistically significant. PRKACA mutant CPAs predominantly exhibited hypomethylation of CYP17A1 gene compared with the GNAS mutant CPAs. Inverse associations between CYP17A1 methylation in three regions of the gene body and its mRNA levels were observed in the NFAs and CPAs. In applying clustering analysis using CYP17A1 methylation and mRNA levels, CPAs with PRKACA mutation were differentiated from NFAs and CPAs with a GNAS mutation. We demonstrated that CPAs exhibited hypomethylation of the CYP17A1 gene body in CPA, especially in the PRKACA mutant CPAs. Methylation of CYP17A1 gene may influence its transcription levels.

Hypomethylation associated vitamin D receptor expression in ATP1A1 mutant aldosterone-producing adenoma.

DNA methylation alteration is tissue-specific and play a pivotal role in regulating gene transcription during cell proliferation and survival. We aimed to detect genes regulated by DNA methylation, and then investigated whether the gene influenced cell proliferation or survival in adrenal cells. DNA methylation and qPCR analyses were performed in nonfunctioning adrenocortical adenoma (NFA, n = 12) and aldosterone-producing adenoma (APA, n = 35) samples. The VDR gene promoter was markedly hypomethylated in APA with ATP1A1 mutation, and the promoter methylation levels showed a significant inverse association with the transcripts in APA. ATP1A1 mutation led to VDR transcription in HAC15 cells, and VDR suppression abrogated ATP1A1 mutation-mediated cell proliferation in HAC15 cells. We demonstrated that APA with ATP1A1 mutation showed entire hypomethylation in the VDR promoter and abundant VDR mRNA and protein expression. VDR suppression abrogated ATP1A1 mutation-mediated cell proliferation in HAC15 cells. Abundant VDR expression would be essential for ATP1A1 mutation-mediated cell proliferation.

Predictive value of the coronary artery calcium score and advanced plaque characteristics: Post hoc analysis of the PREDICT registry.

BACKGROUND: Whether coronary plaque characteristics assessed in coronary computed tomography angiography (CCTA) in association with the coronary artery calcium score (CACS) have predictive value for coronary events is unclear. We aimed to examine the predictive value of the CACS and plaque characteristics for the occurrence of coronary events. METHODS: Among 2802 patients who were analyzed in the PREDICT registry, 2083 with suspected coronary artery disease (CAD) were studied using post hoc analysis. High-risk plaques were defined as having ≥2 adverse characteristics, such as low computed tomographic attenuation, positive remodeling, spotty calcification, and napkin-ring sign. An adjudicative composite of coronary events (cardiac death, nonfatal acute coronary syndrome, and coronary revascularization ≥3 months after indexed CCTA) were analyzed. RESULTS: Seventy-three (3.5%) patients had coronary events and 313 (15.0%) had high-risk plaques. Multivariate Cox proportional hazard analysis showed that high-risk plaques remained an independent predictor of coronary events (adjusted hazard ratio [HR] 1.95, 95% confidence interval [CI] 1.13-3.34, P â€‹= â€‹0.0154), as well as the log-transformed CACS (adjusted HR 1.24, 95% CI 1.11-1.39, P â€‹= â€‹0.0002) and the presence of obstructive stenosis (adjusted HR 5.63, 95% CI 3.22-10.12, P 0.0001). In subgroup analyses, high-risk plaques were independently predictive only in the low CACS class (<100). CONCLUSION: This study shows that assessment of adverse features by coronary plaque imaging independently predicts coronary events in patients with suspected CAD and a low CACS. Our findings suggest that the clinical value of high-risk plaques to CACS and stenosis assessment appears marginal.

Genotype-specific cortisol production associated with Cushing's syndrome adenoma with PRKACA mutations.

The intracellular molecular mechanisms underlying the genotype of cortisol-producing adenoma (CPA) have not been fully determined. We analyzed gene expressions in CPA and the human adrenocortical cell line (HAC15 cells) with PRKACA mutation. Clustering analysis using a gene set associated with responses to cAMP revealed the possible differences between PRKACA mutant CPAs and GNAS and CTNNB1 mutant CPAs. The levels of STAR, CYP11A1, CYP17A1, CYP21A2, and FDX1 transcripts and cortisol levels per unit area in PRKACA mutant CPAs were significantly higher than those in GNAS mutant CPAs. PRKACA mutations led to an increase in steroidogenic enzyme expression and cortisol production in HAC15 cells. Transcriptome analysis revealed differences between PRKACA mutant CPAs and GNAS and CTNNB1 mutant CPAs. Cortisol production in PRKACA mutant CPAs is increased by the cAMP-PKA signaling pathway-mediated upregulation of steroidogenic enzymes transcription. The intracellular molecular mechanisms underlying these processes would be notably important in PRKACA mutant CPAs.

A common disease-associated missense mutation in alpha-sarcoglycan fails to cause muscular dystrophy in mice.

Limb-girdle muscular dystrophy type 2D (LGMD2D) is caused by autosomal recessive mutations in the alpha-sarcoglycan gene. An R77C substitution is the most prevalent cause of the disease, leading to disruption of the sarcoglycan-sarcospan complex. To model this common mutation, we generated knock-in mice with an H77C substitution in alpha-sarcoglycan. The floxed neomycin (Neo)-cassette retained at the targeted H77C alpha-sarcoglycan locus caused a loss of alpha-sarcoglycan expression, resulting in muscular dystrophy in homozygotes, whereas Cre-mediated deletion of the floxed Neo-cassette led to recovered H77C alpha-sarcoglycan expression. Contrary to expectations, mice homozygous for the H77C-encoding allele expressed both this mutant alpha-sarcoglycan and the other components of the sarcoglycan-sarcospan complex in striated muscle, and did not develop muscular dystrophy. Accordingly, conditional rescued expression of the H77C protein in striated muscle of the alpha-sarcoglycan-deficient mice prevented the disease. Adding to the case that the behavior of mutant alpha-sarcoglycan is different between humans and mice, mutant human R77C alpha-sarcoglycan restored the expression of the sarcoglycan-sarcospan complex when introduced by adenoviral vector into the skeletal muscle of previously created alpha-sarcoglycan null mice. These findings indicate that the alpha-sarcoglycan with the most frequent missense mutation in LGMD2D is correctly processed, is transported to the sarcolemma, and is fully functional in mouse muscle. Our study presents an unexpected difference in the behavior of a missense-mutated protein in mice versus human patients, and emphasizes the need to understand species-specific protein quality control systems.

A 50-year history of the health impacts of Westernization on the lifestyle of Japanese Americans: A focus on the Hawaii-Los Angeles-Hiroshima Study.

A medical survey of Japanese Americans have been carried out since 1970; in particular, this survey was administered to the Japanese emigrants from Hiroshima (Japan) to Hawaii or Los Angeles (USA) and their offspring. Labeled the Hawaii-Los Angeles-Hiroshima Study, it constituted a long-term epidemiological study of Japanese Americans who are genetically identical to the native Japanese people, but have experienced rapid and intense Westernization in terms of their lifestyles. The authors have compared the medical survey data procured from two Japanese populations, evincing very disparate lifestyles; that is, the native Japanese inhabitants of Hiroshima (Japan) and Japanese Americans living in Hawaii or Los Angeles (USA). The focus was particularly on differences in the intake of nutrients, the frequency of obesity, the prevalence of metabolic syndrome and diabetes mellitus, and the progression of atherosclerosis. The authors believe that the health effects of the lifestyles of Japanese Americans can predict the imminent health prospects of native Japanese people who adopt Westernized lifestyles in Japan. This review thus summarized the major results accumulated from the Hawaii-Los Angeles-Hiroshima Study over the past 50 years.

Retrograde-angioscopy guided wiring technique in chronic total occlusion lead to successful revascularization.

Endovascular therapy (EVT) was performed in two cases with chronic total occlusion (CTO) of superficial femoral artery. In these cases, angioscopy was deployed in the backyard of the CTO lesion from popliteal artery retrogradely, then the guidewire was advanced from antegrade. When the wire crossed the distal of the CTO lesion, the wire penetration was clearly visualized by the retrograde-angioscopy. Therefore, wire crossing of CTO into the distal true lumen was certainly confirmed, and EVT was successful. .

Angiotensin-converting enzyme 2 expression is not induced by the renin-angiotensin system in the lung.

Pulmonary expression of angiotensin-converting enzyme 2, which is a receptor of severe acute respiratory syndrome coronavirus 2, is not regulated by angiotensin II or renin-angiotensin system inhibitors #COVID19 https://bit.ly/3fkopuO.

Investigations of an inducible intact dystrophin gene excision system in cardiac and skeletal muscle in vivo.

We sought here to induce the excision of a large intragenic segment within the intact dystrophin gene locus, with the ultimate goal to elucidate dystrophin protein function and stability in striated muscles in vivo. To this end, we implemented an inducible-gene excision methodology using a floxed allele approach, demarcated by dystrophin exons 2-79, in complementation with a cardiac and skeletal muscle directed gene deletion system for spatial-temporal control of dystrophin gene excision in vivo. Main findings of this study include evidence of significant intact dystrophin gene excision, ranging from ~ 25% in heart muscle to ~ 30-35% in skeletal muscles in vivo. Results show that despite evidence of significant dystrophin gene excision, no significant decrease in dystrophin protein content was evident by Western blot analysis, at three months post excision in skeletal muscles or by 6 months post gene excision in heart muscle. Challenges of in vivo dystrophin gene excision revealed acute deleterious effects of tamoxifen on striated muscles, including a transient down regulation in dystrophin gene transcription in the absence of dystrophin gene excision. In addition, technical limitations of incomplete dystrophin gene excision became apparent that, in turn, tempered interpretation. Collectively, these findings are in keeping with earlier studies suggesting the dystrophin protein to be long-lived in striated muscles in vivo; however, more rigorous quantitative analysis of dystrophin stability in vivo will require future works in which more complete gene excision can be demonstrated, and without significant off-target effects of the gene deletion experimental platform per se.