Recognizing the opponent: The consolidation of long-term social memory in zebrafish males.

Recognizing and remembering another individual in a social context could be beneficial for individual fitness. Especially in agonistic encounters, remembering an opponent and the previous fight could allow for avoiding new conflicts. Considering this, we hypothesized that this type of social interaction forms a long-term recognition memory lasting several days. It has been shown that a second encounter 24 h later between the same pair of zebrafish males is resolved with lower levels of aggression. Here, we evaluated if this behavioral change could last for longer intervals and a putative mechanism associated with memory storage: the recruitment of NMDA receptors. We found that if a pair of zebrafish males fight and fight again 48 or 72 h later, they resolve the second encounter with lower levels of aggression. However, if opponents were exposed to MK-801 (NMDA receptor antagonist) immediately after the first encounter, they solved the second one with the same levels of aggression: that is, no reduction in aggressive behaviors was observed. These amnesic effect suggest the formation of a long-term social memory related to recognizing a particular opponent and/or the outcome and features of a previous fight.

Italian Association of Hospital Cardiologists Position Paper 'Gender discrepancy: time to implement gender-based clinical management'.

It has been well assessed that women have been widely under-represented in cardiovascular clinical trials. Moreover, a significant discrepancy in pharmacological and interventional strategies has been reported. Therefore, poor outcomes and more significant mortality have been shown in many diseases. Pharmacokinetic and pharmacodynamic differences in drug metabolism have also been described so that effectiveness could be different according to sex. However, awareness about the gender gap remains too scarce. Consequently, gender-specific guidelines are lacking, and the need for a sex-specific approach has become more evident in the last few years. This paper aims to evaluate different therapeutic approaches to managing the most common women's diseases.

Small mitochondrial RNAs as mediators of nuclear gene regulation, and potential implications for human health.

Much research has focused on the effects of pathogenic mitochondrial mutations on health. Notwithstanding, the mechanisms regulating the link between these mutations and their effects remain elusive in several cases. Here, we propose that certain mitochondrial mutations may disrupt function of a set of mitochondrial-transcribed small RNAs, perturbing communication between mitochondria and nucleus, leading to disease. Our hypothesis synthesises two lines of supporting evidence. First, several mitochondrial mutations cannot be directly linked to effects on energy production or protein synthesis. Second, emerging studies have described the existence of small RNAs encoded by the mitochondria and proposed their involvement in RNA interference. We present a roadmap to testing this hypothesis.

Fragmentation in mitochondrial genomes in relation to elevated sequence divergence and extreme rearrangements.

BACKGROUND: A single circular mitochondrial (mt) genome is a common feature across most metazoans. The mt-genome includes protein-coding genes involved in oxidative phosphorylation, as well as RNAs necessary for translation of mt-RNAs, whose order and number are highly conserved across animal clades, with few known exceptions of alternative mt-gene order or mt-genome architectures. One such exception consists of the fragmented mitochondrial genome, a type of genome architecture where mt-genes are split across two or more mt-chromosomes. However, the origins of mt-genome fragmentation and its effects on mt-genome evolution are unknown. Here, we investigate these origin and potential mechanisms underlying mt-genome fragmentation, focusing on a genus of booklice, Liposcelis, which exhibits elevated sequence divergence, frequent rearrangement of mt-gene order, and fragmentation of the mt genome, and compare them to other Metazoan clades. RESULTS: We found this genus Liposcelis exhibits very low conservation of mt-gene order across species, relative to other metazoans. Levels of gene order rearrangement were, however, unrelated to whether or not mt-genomes were fragmented or intact, suggesting mitochondrial genome fragmentation is not affecting mt-gene order directly. We further investigated possible mechanisms underpinning these patterns and revealed very high conservation of non-coding sequences at the edges of multiple recombination regions across populations of one particular Liposcelis species, supportive of a hypothesis that mt-fragmentation arises from recombination errors between mt-genome copies. We propose these errors may arise as a consequence of a heightened mutation rate in clades exhibiting mt-fragmentation. Consistent with this, we observed a striking pattern across three Metazoan phyla (Arthropoda, Nematoda, Cnidaria) characterised by members exhibiting high levels of mt-gene order rearrangement and cases of mt-fragmentation, whereby the mt-genomes of species more closely related to species with fragmented mt-genomes diverge more rapidly despite experiencing strong purifying selection. CONCLUSIONS: We showed that contrary to expectations, mt-genome fragmentation is not correlated with the increase in mt-genome rearrangements. Furthermore, we present evidence that fragmentation of the mt-genome may be part of a general relaxation of a natural selection on the mt-genome, thus providing new insights into the origins of mt-genome fragmentation and evolution.

Optimizing Battery Charging Using Neural Networks in the Presence of Unknown States and Parameters.

This work investigates the effectiveness of deep neural networks within the realm of battery charging. This is done by introducing an innovative control methodology that not only ensures safety and optimizes the charging current, but also substantially reduces the computational complexity with respect to traditional model-based approaches. In addition to their high computational costs, model-based approaches are also hindered by their need to accurately know the model parameters and the internal states of the battery, which are typically unmeasurable in a realistic scenario. In this regard, the deep learning-based methodology described in this work was been applied for the first time to the best of the authors' knowledge, to scenarios where the battery's internal states cannot be measured and an estimate of the battery's parameters is unavailable. The reported results from the statistical validation of such a methodology underline the efficacy of this approach in approximating the optimal charging policy.

Olfactory subsystems in the peripheral olfactory organ of anuran amphibians.

Anuran amphibians (frogs and toads) typically have a complex life cycle, involving aquatic larvae that metamorphose to semi-terrestrial juveniles and adults. However, the anuran olfactory system is best known in Xenopus laevis, an animal with secondarily aquatic adults. The larval olfactory organ contains two distinct sensory epithelia: the olfactory epithelium (OE) and vomeronasal organ (VNO). The adult organ contains three: the OE, the VNO, and a "middle cavity" epithelium (MCE), each in its own chamber. The sensory epithelia of Xenopus larvae have overlapping sensory neuron morphology (ciliated or microvillus) and olfactory receptor gene expression. The MCE of adults closely resembles the OE of larvae, and senses waterborne odorants; the adult OE is distinct and senses airborne odorants. Olfactory subsystems in other (non-pipid) anurans are diverse. Many anuran larvae show a patch of olfactory epithelium exposed in the buccal cavity (bOE), associated with a grazing feeding mode. And other anuran adults do not have a sensory MCE, but many have a distinct patch of epithelium adjacent to the OE, the recessus olfactorius (RO), which senses waterborne odorants. Olfaction plays a wide variety of roles in the life of larval and adult anurans, and some progress has been made in identifying relevant odorants, including pheromones and feeding cues. Increased knowledge of the diversity of olfactory structure, of odorant receptor expression patterns, and of factors that affect the access of odorants to sensory epithelia will enable us to better understand the adaptation of the anuran olfactory system to aquatic and terrestrial environments.

Implications of atrial fibrillation on the clinical course and outcomes of hospitalized COVID-19 patients: results of the Cardio-COVID-Italy multicentre study.

AIMS: To assess the clinical relevance of a history of atrial fibrillation (AF) in hospitalized patients with coronavirus disease 2019 (COVID-19). METHODS AND RESULTS: We enrolled 696 consecutive patients (mean age 67.4 ± 13.2 years, 69.7% males) admitted for COVID-19 in 13 Italian cardiology centres between 1 March and 9 April 2020. One hundred and six patients (15%) had a history of AF and the median hospitalization length was 14 days (interquartile range 9-24). Patients with a history of AF were older and with a higher burden of cardiovascular risk factors. Compared to patients without AF, they showed a higher rate of in-hospital death (38.7% vs. 20.8%; P < 0.001). History of AF was associated with an increased risk of death after adjustment for clinical confounders related to COVID-19 severity and cardiovascular comorbidities, including history of heart failure (HF) and increased plasma troponin [adjusted hazard ratio (HR): 1.73; 95% confidence interval (CI) 1.06-2.84; P = 0.029]. Patients with a history of AF also had more in-hospital clinical events including new-onset AF (36.8% vs. 7.9%; P < 0.001), acute HF (25.3% vs. 6.3%; P < 0.001), and multiorgan failure (13.9% vs. 5.8%; P = 0.010). The association between AF and worse outcome was not modified by previous or concomitant use of anticoagulants or steroid therapy (P for interaction >0.05 for both) and was not related to stroke or bleeding events. CONCLUSION: Among hospitalized patients with COVID-19, a history of AF contributes to worse clinical course with a higher mortality and in-hospital events including new-onset AF, acute HF, and multiorgan failure. The mortality risk remains significant after adjustment for variables associated with COVID-19 severity and comorbidities.

Prognostic Implications of Congestion on Physical Examination Among Contemporary Patients With Heart Failure and Reduced Ejection Fraction: PARADIGM-HF.

BACKGROUND: The contemporary prognostic value of the physical examination- beyond traditional risk factors including natriuretic peptides, risk scores, and symptoms-in heart failure (HF) with reduced ejection fraction is unknown. We aimed to determine the association between physical signs of congestion at baseline and during study follow-up with quality of life and clinical outcomes and to assess the treatment effects of sacubitril/valsartan on congestion. METHODS: We analyzed participants from PARADIGM-HF (Prospective Comparison of Angiotensin Receptor-Neprilysin Inhibitor With Angiotensin Converting Enzyme Inhibitor to Determine Impact on Global Mortality and Morbidity in HF) with an available physical examination at baseline. We examined the association of the number of signs of congestion (jugular venous distention, edema, rales, and third heart sound) with the primary outcome (cardiovascular death or HF hospitalization), its individual components, and all-cause mortality using time-updated, multivariable-adjusted Cox regression. We further evaluated whether sacubitril/valsartan reduced congestion during follow-up and whether improvement in congestion is related to changes in clinical outcomes and quality of life, assessed by Kansas City Cardiomyopathy Questionnaire overall summary scores. RESULTS: Among 8380 participants, 0, 1, 2, and 3+ signs of congestion were present in 70%, 21%, 7%, and 2% of patients, respectively. Patients with baseline congestion were older, more often female, had higher MAGGIC risk scores (Meta-Analysis Global Group in Chronic Heart Failure) and lower Kansas City Cardiomyopathy Questionnaire overall summary scores (P<0.05). After adjusting for baseline natriuretic peptides, time-updated Meta-Analysis Global Group in Chronic Heart Failure score, and time-updated New York Heart Association class, increasing time-updated congestion was associated with all outcomes (P<0.001). Sacubitril/valsartan reduced the risk of the primary outcome irrespective of clinical signs of congestion at baseline (P=0.16 for interaction), and treatment with the drug improved congestion to a greater extent than did enalapril (P=0.011). Each 1-sign reduction was independently associated with a 5.1 (95% CI, 4.7-5.5) point improvement in Kansas City Cardiomyopathy Questionnaire overall summary scores. Change in congestion strongly predicted outcomes even after adjusting for baseline congestion (P<0.001). CONCLUSIONS: In HF with reduced ejection fraction, the physical exam continues to provide significant independent prognostic value even beyond symptoms, natriuretic peptides, and Meta-Analysis Global Group in Chronic Heart Failure risk score. Sacubitril/valsartan improved congestion to a greater extent than did enalapril. Reducing congestion in the outpatient setting is independently associated with improved quality of life and reduced cardiovascular events, including mortality. CLINICAL TRIAL REGISTRATION: https://www.clinicaltrials.gov. Unique identifier: NCT01035255.

An integrated interdisciplinary approach to evaluate potentially toxic element sources in a mountainous watershed.

Potentially toxic elements (PTEs, i.e., Cd, Ni, Cr) and their source apportionment in waters are of major environmental concern. Different approaches can be used to evaluate PTEs sources in environment, but single-way approaches are often limited and can easily fail. PTEs sources apportionment should include the evaluation of geochemical background and spatiotemporal trends analyses. We propose an integrated approach, and we apply it to a mountain catchment in the Italian central Alps, where ultramafic terranes crop out. We collected water and glacial sediment samples during the melting season. Then, we analyzed major ions and PTEs in waters, and we quantified the total PTEs load in sediments through acid digestion. Data were then processed through spatial and temporal trends analysis, clustering of variables and the evaluation of partition between the different compartments. We found a high geochemical background of part of the PTEs, consistently with results from other areas worldwide on mafic and ultramafic terranes (high concentrations of Ni, Cr and Fe), while we identified an additional atmospheric deposition source for Zn, Cd and Ag. Also, redundant observations on Cu, As and Pb indicated a possible mixed source. This study elucidates the need for an integrated approach to avoid unnecessary or misleading assumptions in the PTE's source appointment. A single-way approach application, in fact, can fail in understanding element source in a complicated and dynamic compartment like surface water.

Movement Control Impairment and Low Back Pain: State of the Art of Diagnostic Framing.

Background and objectives: Low back pain is one of the most common health problems. In 85% of cases, it is not possible to identify a specific cause, and it is therefore called Non-Specific Low Back Pain (NSLBP). Among the various attempted classifications, the subgroup of patients with impairment of motor control of the lower back (MCI) is between the most studied. The objective of this systematic review is to summarize the results from trials about validity and reliability of clinical tests aimed to identify MCI in the NSLBP population. Materials and Methods: The MEDLINE, Cochrane Library, and MedNar databases have been searched until May 2018. The criteria for inclusion were clinical trials about evaluation methods that are affordable and applicable in a usual clinical setting and conducted on populations aged > 18 years. A single author summarized data in synoptic tables relating to the clinical property; a second reviewer intervened in case of doubts about the relevance of the studies. Results: 13 primary studies met the inclusion criteria: 10 investigated inter-rater reliability, 4 investigated intra-rater reliability, and 6 investigated validity for a total of 23 tests (including one cluster of tests). Inter-rater reliability is widely studied, and there are tests with good, consistent, and substantial values (waiter's bow, prone hip extension, sitting knee extension, and one leg stance). Intra-rater reliability has been less investigated, and no test have been studied for more than one author. The results of the few studies about validity aim to discriminate only the presence or absence of LBP in the samples. Conclusions: At the state of the art, results related to reliability support the clinical use of the identified tests. No conclusions can be drawn about validity.

SmithRNAs: Could Mitochondria "Bend" Nuclear Regulation?

Typically, animal mitochondria have very compact genomes, with few short intergenic regions, and no introns. Hence, it may seem that there is little space for unknown functions in mitochondrial DNA (mtDNA). However, mtDNA can also operate through RNA interference, as small non coding RNAs (sncRNAs) produced by mtDNA have already been proposed for humans. We sequenced sncRNA libraries from isolated mitochondria of Ruditapes philippinarum (Mollusca Bivalvia) gonads, a species with doubly uniparental inheritance of mitochondria, and identified several putative sncRNAs of mitochondrial origin. Some sncRNAs are transcribed by intergenic regions that form stable stem-hairpin structures, which makes them good miRNA-like candidates. We decided to name them small mitochondrial highly-transcribed RNAs (smithRNAs). Many concurrent data support that we have recovered sncRNAs of mitochondrial origin that might be involved in gonad formation and able to affect nuclear gene expression. This possibility has been never suggested before. If mtDNA can affect nuclear gene expression through RNA interference, this opens a plethora of new possibilities for it to interact with the nucleus, and makes metazoan mtDNA a much more complex genome than previously thought.

Addressing the Heterogeneity of Heart Failure in Future Randomized Trials.

PURPOSE OF THE REVIEW: The aim of review is to describe the essential role of study designs beyond RCTs in contemporary contest of HF patients giving perspectives on its evolving. The article concludes with concern about the support of observational studies for future randomized clinical trials. RECENT FINDINGS: With the aging population and spectacular advance in cardiovascular therapy, the clinical syndrome comprising heart failure (HF) is increasingly in complexity of heterogeneity. It remains among the most challenging of clinical syndromes with a magnitude of proposed pathophysiological mechanisms involving the heart and the interplay with cardiac and non-cardiac comorbidities. In this epidemiological scenario, randomized clinical trials are suffering from growing failed treatment, so that a deeper understanding of heterogeneity represents a major unmet need. This field also is greatly in a more nuanced comprehension about the applicability in clinical practice of trials' results derived from well-selected HF population. Thus, we need to reflect on trials failures and the translation of previous trials in clinical practice in order to redirect the future trial intervention.

Ancestry affects the transcription of small mitochondrial RNAs in human lymphocytes.

Mitochondrial mutations have been linked to changes in phenotypes such as fertility or longevity, however, these changes have been often inconsistent across populations for unknown reasons. A hypothesis that could explain this inconsistency is that some still uncharacterized mitochondrial products are mediating the phenotypic changes across populations. It has been hypothesized that one such product could be the small RNAs encoded in the mitochondrial genome, thus this work will provide new evidence for their existence and function. By using data from the 1000 genome project and knowledge from previously characterized nuclear small RNAs, this study found that 10 small RNAs encoded in tRNA fragments are consistently expressed in 450 individuals from five different populations. Furthermore, this study demonstrated that the expression of some small mitochondrial RNAs is different in individuals of African ancestry, similar to what was observed before in nuclear and mitochondria mRNAs. Lastly, we investigate the causes behind these differences in expression, showing that at least one of the mt-tRFs might be regulated by TRMT10B. The analyses presented in this work further support the small mitochondrial RNAs as functional molecules, and their population-specific expression supports the hypothesis that they act as a mediator between the nucleus and mitochondria differently across populations.

Epidermal club cells in the cardinal tetra (Paracheirodon axelrodi): Presence, distribution, and relationship to antipredator behavior.

Epidermal club cells (ECCs) are present in many species of teleost fish. In an attempt to justify their presence in the epidermis of fish, they have been associated with numerous functions. One proposed function is communication with conspecifics during a predation event, as these cells may passively release substances upon rupture, which may occur during predation. We identified the presence and distribution of ECCs in the body skin of adult cardinal tetra, Paracheirodon axelrodi (Schultz, 1956) and analyzed the animal's behavioral response to conspecific skin extract in a laboratory setting. The identification and distribution of ECCs in the epidermis of the animals were confirmed by conventional histology and immunohistochemistry. Our results demonstrated that: ECCs are present in the skin of the entire body; a high density is observed in the dorsal side from head to tail, in the insertion of the fins and in the epidermis covering them; and ventral distribution is less extensive and more dispersed than dorsal distribution. Treatment of P. axelrodi specimens with skin preparations of conspecifics resulted in behavioral changes in the animals: they showed erratic swimming movements, they showed avoidance of the area of stimulus application and they decreased the time spent moving. Overall, these results allow us to conclude that P. axelrodi possesses ECCs throughout the body, with a greater presence in areas of high exposure to predation events (dorsal area and fins). Animals exposed to conspecific skin extract showed a significant increase in behaviors described as anti-predatory in other species. This supports the hypothesis that ECCs may be the origin of chemical alarm cues that are passively released when skin damage occurs, alerting the rest of the group to the risk of predation.

Inotropic Agents: Are We Still in the Middle of Nowhere?

Inotropes are prescribed to enhance myocardial contractility while vasopressors serve to improve vascular tone. Although these medications remain a life-saving therapy in cardiovascular clinical scenarios with hemodynamic impairment, the paucity of evidence on these drugs makes the choice of the most appropriate vasoactive agent challenging. As such, deep knowledge of their pharmacological and hemodynamic effects becomes crucial to optimizing hemodynamic profile while reducing the potential adverse effects. Given this perspective, it is imperative for cardiologists to possess a comprehensive understanding of the underlying mechanisms governing these agents and to discern optimal strategies for their application across diverse clinical contexts. Thus, we briefly review these agents' pharmacological and hemodynamic properties and their reasonable clinical applications in cardiovascular settings. Critical interpretation of available data and the opportunities for future investigations are also highlighted.

Coagulation Tests and Reversal Agents in Patients Treated with Oral Anticoagulants: The Challenging Scenarios of Life-Threatening Bleeding and Unplanned Invasive Procedures.

In clinical practice, the number of patients treated with direct oral anticoagulants (DOACs) has consistently increased over the years. Since anticoagulant therapy has been associated with an annual incidence of major bleeding (MB) events of approximately 2% to 3.5%, it is of paramount importance to understand how to manage anticoagulated patients with major or life-threatening bleeding. A considerable number of these patients' conditions necessitate hospitalization, and the administration of reversal agents may be imperative to manage and control bleeding episodes effectively. Importantly, effective strategies for reversing the anticoagulant effects of DOACs have been well recognized. Specifically, idarucizumab has obtained regulatory approval for the reversal of dabigatran, and andexanet alfa has recently been approved for reversing the effects of apixaban or rivaroxaban in patients experiencing life-threatening or uncontrolled bleeding events. Moreover, continuous endeavors are being made to develop supplementary reversal agents. In emergency scenarios where specific reversal agents might not be accessible, non-specific hemostatic agents such as prothrombin complex concentrate can be utilized to neutralize the anticoagulant effects of DOACs. However, it is paramount to emphasize that specific reversal agents, characterized by their efficacy and safety, should be the preferred choice when suitable. Moreover, it is worth noting that adherence to the guidelines for the reversal agents is poor, and there is a notable gap between international recommendations and actual clinical practices in this regard. This narrative review aims to provide physicians with a practical approach to managing specific reversal agents.

Anderson-Fabry Disease: Red Flags for Early Diagnosis of Cardiac Involvement.

Anderson-Fabry disease (AFD) is a lysosome storage disorder resulting from an X-linked inheritance of a mutation in the galactosidase A (GLA) gene encoding for the enzyme alpha-galactosidase A (α-GAL A). This mutation results in a deficiency or absence of α-GAL A activity, with a progressive intracellular deposition of glycosphingolipids leading to organ dysfunction and failure. Cardiac damage starts early in life, often occurring sub-clinically before overt cardiac symptoms. Left ventricular hypertrophy represents a common cardiac manifestation, albeit conduction system impairment, arrhythmias, and valvular abnormalities may also characterize AFD. Even in consideration of pleiotropic manifestation, diagnosis is often challenging. Thus, knowledge of cardiac and extracardiac diagnostic "red flags" is needed to guide a timely diagnosis. Indeed, considering its systemic involvement, a multidisciplinary approach may be helpful in discerning AFD-related cardiac disease. Beyond clinical pearls, a practical approach to assist clinicians in diagnosing AFD includes optimal management of biochemical tests, genetic tests, and cardiac biopsy. We extensively reviewed the current literature on AFD cardiomyopathy, focusing on cardiac "red flags" that may represent key diagnostic tools to establish a timely diagnosis. Furthermore, clinical findings to identify patients at higher risk of sudden death are also highlighted.

Heart Failure with Preserved Ejection Fraction: How to Deal with This Chameleon.

Heart failure with preserved ejection fraction (HFpEF) is characterized by a notable heterogeneity in both phenotypic and pathophysiological features, with a growing incidence due to the increase in median age and comorbidities such as obesity, arterial hypertension, and cardiometabolic disease. In recent decades, the development of new pharmacological and non-pharmacological options has significantly impacted outcomes, improving clinical status and reducing mortality. Moreover, a more personalized and accurate therapeutic management has been demonstrated to enhance the quality of life, diminish hospitalizations, and improve overall survival. Therefore, assessing the peculiarities of patients with HFpEF is crucial in order to obtain a better understanding of this disorder. Importantly, comorbidities have been shown to influence symptoms and prognosis, and, consequently, they should be carefully addressed. In this sense, it is mandatory to join forces with a multidisciplinary team in order to achieve high-quality care. However, HFpEF remains largely under-recognized and under-treated in clinical practice, and the diagnostic and therapeutic management of these patients remains challenging. The aim of this paper is to articulate a pragmatic approach for patients with HFpEF focusing on the etiology, diagnosis, and treatment of HFpEF.

[Gender discrepancy: time to implement gender-based clinical management]. / Position paper ANMCO: Differenze di genere nell'approccio farmacologico cardiovascolare.

It is well established that gender strongly influences cardiovascular risk factors, playing a crucial role in cardiovascular prevention, clinical pathways, diagnostic approach and treatment. Beyond the sex, which is a biological factor, gender entails a socio-cultural condition that impacts access and quality of care due to structural and institutional barriers. However, despite its great importance, this issue has not been adequately covered. Indeed sex and gender differences scarcely impact the clinical approach, creating a lot of disparities in care and outcomes of patients. Therefore, it becomes essential to increase the awareness of the importance of sex and gender influences on cardiovascular diseases. Moreover, new strategies for reducing disparities should be developed. Importantly, these differences should be taken into account in guideline recommendations. In this regard, it is crucial to include a greater number of women in clinical trials, since they are currently underrepresented. Furthermore, more women should be involved as member of international boards in order to develop recommendations and guidelines with more attention to this important topic.The aim of this ANMCO position paper is to shed light on gender differences concerning many cardiovascular drugs in order to encourage a more personalized therapeutic approach.

AT1 receptor blockade delays postlactational mammary gland involution: a novel role for the renin angiotensin system.

Angiotensin II (AngII), the main effector peptide of the renin-angiotensin system (RAS), participates in multiple biological processes, including cell growth, apoptosis, and tissue remodeling. Since AngII activates, in different cell types, signal transducing pathways that are critical for mammary gland postlactational regression, we investigated the role of the RAS during this process. We found that exogenous administration of AngII in mammary glands of lactating Balb/c mice induced epithelium apoptosis [2.9±0.5% (control) vs. 9.6±1.1% (AngII); P < 0.001] and activation of the proapoptotic factor STAT3, an effect inhibited by irbesartan, an AT(1) receptor blocker. Subsequently, we studied the expression kinetics of RAS components during involution. We found that angiotensin-converting enzyme (ACE) mRNA expression peaked 6 h after weaning (5.7-fold; P<0.01), while induction of angiotensinogen and AT(1) and AT(2) receptors expression was detected 96 h after weaning (6.2-, 10-, and 6.2-fold increase, respectively; P<0.01). To assess the role of endogenously generated AngII, mice were treated with losartan, an AT(1) receptor blocker, during mammary involution. Mammary glands from losartan-treated mice showed activation of the survival factors AKT and BCL-(XL), significantly lower LIF and TNF-α mRNA expression (P<0.05), reduced apoptosis [12.1±2.1% (control) vs. 4.8±0.7% (losartan); P<0.001] and shedding of epithelial cells, inhibition of MMP-9 activity in a dose-dependent manner (80%; P<0.05; with losartan IC(50) value of 6.9 mg/kg/d] and lower collagen deposition and adipocyte invasion causing a delayed involution compared to vehicle-treated mice. Furthermore, mammary glands of forced weaned AT(1A)- and/or AT(1B)-deficient mice exhibited retarded apoptosis of epithelial cells [6.3±0.95% (WT) vs. 3.3±0.56% (AT(1A)/AT(1B) DKO); P<0.05] with remarkable delayed postlactational regression compared to wild-type animals. Taken together, these results strongly suggest that AngII, via the AT(1) receptor, plays a major role in mouse mammary gland involution identifying a novel role for the RAS. angiotensin system.