The gut microbiota prime systemic antiviral immunity via the cGAS-STING-IFN-I axis.

The microbiota are vital for immune homeostasis and provide a competitive barrier to bacterial and fungal pathogens. Here, we investigated how gut commensals modulate systemic immunity and response to viral infection. Antibiotic suppression of the gut microbiota reduced systemic tonic type I interferon (IFN-I) and antiviral priming. The microbiota-driven tonic IFN-I-response was dependent on cGAS-STING but not on TLR signaling or direct host-bacteria interactions. Instead, membrane vesicles (MVs) from extracellular bacteria activated the cGAS-STING-IFN-I axis by delivering bacterial DNA into distal host cells. DNA-containing MVs from the gut microbiota were found in circulation and promoted the clearance of both DNA (herpes simplex virus type 1) and RNA (vesicular stomatitis virus) viruses in a cGAS-dependent manner. In summary, this study establishes an important role for the microbiota in peripheral cGAS-STING activation, which promotes host resistance to systemic viral infections. Moreover, it uncovers an underappreciated risk of antibiotic use during viral infections.

The crosstalk between DNA repair and immune responses.

In recent years, increasing evidence has highlighted the profound connection between DNA damage repair and the activation of immune responses. We spoke with researchers about their mechanistic interplays and the implications for cancer and other diseases.

Loss of the DNA Damage Repair Kinase ATM Impairs Inflammasome-Dependent Anti-Bacterial Innate Immunity.

The ATM kinase is a central component of the DNA damage repair machinery and redox balance. ATM dysfunction results in the multisystem disease ataxia-telangiectasia (AT). A major cause of mortality in AT is respiratory bacterial infections. Whether ATM deficiency causes innate immune defects that might contribute to bacterial infections is not known. Here we have shown that loss of ATM impairs inflammasome-dependent anti-bacterial innate immunity. Cells from AT patients or Atm(-/-) mice exhibited diminished interleukin-1ß (IL-1ß) production in response to bacteria. In vivo, Atm(-/-) mice were more susceptible to pulmonary S. pneumoniae infection in a manner consistent with inflammasome defects. Our data indicate that such defects were due to oxidative inhibition of inflammasome complex assembly. This study reveals an unanticipated function of reactive oxygen species (ROS) in negative regulation of inflammasomes and proposes a theory for the notable susceptibility of AT patients to pulmonary bacterial infection.

Deubiquitinase MYSM1 Regulates Innate Immunity through Inactivation of TRAF3 and TRAF6 Complexes.

Pattern-recognition receptors (PRRs) including Toll-like receptors, RIG-I-like receptors, and cytoplasmic DNA receptors are essential for protection against pathogens but require tight control to avert inflammatory diseases. The mechanisms underlying this strict regulation are unclear. MYSM1 was previously described as a key component of epigenetic signaling machinery. We found that in response to microbial stimuli, MYSM1 accumulated in the cytoplasm where it interacted with and inactivated TRAF3 and TRAF6 complexes to terminate PRR pathways for pro-inflammatory and type I interferon responses. Consequently, Mysm1 deficiency in mice resulted in hyper-inflammation and enhanced viral clearance but also susceptibility to septic shock. We identified two motifs in MYSM1 that were essential for innate immune suppression: the SWIRM domain that interacted with TRAF3 and TRAF6 and the metalloproteinase domain that removed K63 polyubiquitins. This study identifies MYSM1 as a key negative regulator of the innate immune system that guards against an overzealous self-destructive immune response.

DNA damage primes the type I interferon system via the cytosolic DNA sensor STING to promote anti-microbial innate immunity.

Dysfunction in Ataxia-telangiectasia mutated (ATM), a central component of the DNA repair machinery, results in Ataxia Telangiectasia (AT), a cancer-prone disease with a variety of inflammatory manifestations. By analyzing AT patient samples and Atm(-/-) mice, we found that unrepaired DNA lesions induce type I interferons (IFNs), resulting in enhanced anti-viral and anti-bacterial responses in Atm(-/-) mice. Priming of the type I interferon system by DNA damage involved release of DNA into the cytoplasm where it activated the cytosolic DNA sensing STING-mediated pathway, which in turn enhanced responses to innate stimuli by activating the expression of Toll-like receptors, RIG-I-like receptors, cytoplasmic DNA sensors, and their downstream signaling partners. This study provides a potential explanation for the inflammatory phenotype of AT patients and establishes damaged DNA as a cell intrinsic danger signal that primes the innate immune system for a rapid and amplified response to microbial and environmental threats.

Bacterial detection by NAIP/NLRC4 elicits prompt contractions of intestinal epithelial cell layers.

The gut epithelium serves to maximize the surface for nutrient and fluid uptake, but at the same time must provide a tight barrier to pathogens and remove damaged intestinal epithelial cells (IECs) without jeopardizing barrier integrity. How the epithelium coordinates these tasks remains a question of significant interest. We used imaging and an optical flow analysis pipeline to study the dynamicity of untransformed murine and human intestinal epithelia, cultured atop flexible hydrogel supports. Infection with the pathogen Salmonella Typhimurium (STm) within minutes elicited focal contractions with inward movements of up to ∼1,000 IECs. Genetics approaches and chimeric epithelial monolayers revealed contractions to be triggered by the NAIP/NLRC4 inflammasome, which sensed type-III secretion system and flagellar ligands upon bacterial invasion, converting the local tissue into a contraction epicenter. Execution of the response required swift sublytic Gasdermin D pore formation, ion fluxes, and the propagation of a myosin contraction pulse across the tissue. Importantly, focal contractions preceded, and could be uncoupled from, the death and expulsion of infected IECs. In both two-dimensional monolayers and three-dimensional enteroids, multiple infection-elicited contractions coalesced to produce shrinkage of the epithelium as a whole. Monolayers deficient for Caspase-1(-11) or Gasdermin D failed to elicit focal contractions but were still capable of infected IEC death and expulsion. Strikingly, these monolayers lost their integrity to a markedly higher extent than wild-type counterparts. We propose that prompt NAIP/NLRC4/Caspase-1/Gasdermin D/myosin-dependent contractions allow the epithelium to densify its cell packing in infected regions, thereby preventing tissue disintegration due to the subsequent IEC death and expulsion process.

Disseminated peritoneal leiomyomatosis: A benign condition with diagnostic and therapeutic challenges.

Background: Disseminated peritoneal leiomyomatosis (DPL) is a variant of parasitic leiomyomas that is characterized by multiple peritoneal and subperitoneal nodules of proliferating smooth muscle cells that histologically resemble uterine leiomyoma. We report a case of recurrent DPL to highlight its diagnostic and therapeutic challenges at the Federal Medical Centre, Keffi, Nigeria. Case Report: The patient is a 25-year-old woman with a previous history of myomectomy 3 years before presentation to the hematology unit on account of abdominal lymphoma. Based on the working diagnosis, she was referred to the general surgery unit for an open biopsy and cytoreductive surgery. She was explored, and intraoperative findings were in keeping with multiple well-circumscribed intra-abdominal masses of varying sizes. The multiple and widespread locations of the masses precluded the complete removal of the masses. Four months post-surgery, she presented with similar lesions and had a repeat laparotomy. At the surgery, she had a total abdominal hysterectomy with bilateral salpingophorectomy and excision of the abdominal masses. She was then placed on letrozole, which prevented further tumor growth and abated her symptoms. Discussion: DPL is often rarely diagnosed preoperatively and thus poses a diagnostic challenge, with many cases asymptomatic and therapeutic challenges due to its tendency to recur. Its management currently lacks consensus and is often determined by many factors, such as the age of the patients, the number of nodules, and the desire to have more children, among others. Surgical excision combined with hormonal therapy is recommended for patients who wish to conceive. For postmenopausal women and those who no longer desire conception, total abdominal hysterectomy with bilateral salpingo-oophorectomy should be considered to prevent recurrence. Conclusion: DPL is a rare form of multiple extrauterine leiomyomas. We report a case of DPL in a woman that was managed with surgical intervention and hormonal manipulation therapy following the failure of the initial surgical excision alone. We thus suggest a combination of surgical intervention and postoperative hormonal manipulation in its management, as such a multi-modality of therapy was employed in the index case without evidence of recurrence after a year post-surgery.

Chromatin-bound cGAS is an inhibitor of DNA repair and hence accelerates genome destabilization and cell death.

DNA repair via homologous recombination (HR) is indispensable for genome integrity and cell survival but if unrestrained can result in undesired chromosomal rearrangements. The regulatory mechanisms of HR are not fully understood. Cyclic GMP-AMP synthase (cGAS) is best known as a cytosolic innate immune sensor critical for the outcome of infections, inflammatory diseases, and cancer. Here, we report that cGAS is primarily a chromatin-bound protein that inhibits DNA repair by HR, thereby accelerating genome destabilization, micronucleus generation, and cell death under conditions of genomic stress. This function is independent of the canonical STING-dependent innate immune activation and is physiologically relevant for irradiation-induced depletion of bone marrow cells in mice. Mechanistically, we demonstrate that inhibition of HR repair by cGAS is linked to its ability to self-oligomerize, causing compaction of bound template dsDNA into a higher-ordered state less amenable to strand invasion by RAD51-coated ssDNA filaments. This previously unknown role of cGAS has implications for understanding its involvement in genome instability-associated disorders including cancer.

Rooftop water harvesting for managed aquifer recharge and flood mitigation in tropical cities: Towards a strategy of co-benefit evaluations in João Pessoa, northeast Brazil.

Intense urbanisation in many coastal areas has led to intensification of groundwater consumption, while reducing permeable areas and increasing the frequency and magnitude of flooding. Among the potential strategies to compensate for these adverse effects, which are expected to become worse as a result of climate change, rooftop rainwater harvesting (RWH) in combination with managed aquifer recharge (MAR), may be indicated. This work investigated the performance of different configurations of such a system, tested as a twofold sustainable stormwater and domestic water management tool in a tropical metropole (João Pessoa, Brazil). This area located over a sedimentary aquifer system illustrates the water security challenges of densely urbanised areas in southern cities. To that end, several configurations of rooftop catchments and storage volumes were evaluated, by simulating a MAR-RWH system connected to the regional unconfined aquifer (Barreiras Formation) through a 6″ diameter injection well. Rainfall-runoff-recharge processes and water balances were simulated using monitored high-temporal resolution rainfall data. The results showed that catchments ranging from 180 to 810 m2, connected to tanks from 0.5 to 30.0 m³, are the optimal solutions in terms of efficient rainwater retention and peak flow reduction. These solutions provided mean annual estimates of aquifer recharge between 57 and 255 m³/yr from 2004 to 2019. The results of this study highlight the opportunity for MAR schemes to reconcile stormwater management and water supply goals.

"If Their Face Starts Turning Purple, You Are Probably Doing Something Wrong": Young Men's Experiences with Choking During Sex.

Choking/strangulation during sex has become prevalent in the United States. Yet, no qualitative research has addressed men's choking experiences. Through interviews with 21 young adult men, we examined the language men use to refer to choking, how they first learned about it, their experiences with choking, and consent and safety practices. Men learned about choking during adolescence from pornography, partners, friends, and mainstream media. They engaged in choking to be kinky, adventurous, and to please partners. While many enjoyed or felt neutral about choking, others were reluctant to choke or be choked. Safety and verbal/non-verbal consent practices varied widely.

Genetic connectivity of trypanosomes between tsetse-infested and tsetse-free areas of Kenya.

The prevalence rates of trypanosomes, including those that require cyclical transmission by tsetse flies, are widely distributed in Africa. Trypanosoma brucei and Trypanosoma congolense are actively maintained in regions where there are no tsetse flies although at low frequencies. Whether this could be due to an independent evolutionary origin or multiple introduction of trypanosomes due to continuous movement of livestock between tsetse-free and -infested areas is not known. Thus, the aim of the study was to carry out microsatellite genotyping to explore intra-specific genetic diversity between T. (Trypanozoon), T. congolense and Trypanosoma vivax from the two regions: tsetse infested and tsetse free. Microsatellite genotyping showed geographical origin-based structuring among T. (Trypanozoon) isolates. There was a clear separation between isolates from the two regions signalling the potential of microsatellite markers as diagnostic markers for T. brucei and Trypanosoma evansi isolates. Trypanosoma vivax isolates also clustered largely based on the sampling location with a significant differentiation between the two locations. However, our results revealed that T. congolense isolates from Northern Kenya are not genetically separated from those from Coastal Kenya. Therefore, these isolates are likely introduced in the region through animal movement. Our results demonstrate the occurrence of both genetic connectivity as well as independent evolutionary origin, depending on the trypanosome species between the two ecologies.

Balloon dilatation versus surgical valvotomy for congenital aortic stenosis: a propensity score matched study.

BACKGROUND: Balloon valvuloplasty and surgical aortic valvotomy have been the treatment mainstays for congenital aortic stenosis in children. Choice of intervention often differs depending upon centre bias with limited relevant, comparative literature. OBJECTIVES: This study aims to provide an unbiased, contemporary matched comparison of these balloon and surgical approaches. METHODS: Retrospective analysis of patients with congenital aortic valve stenosis who underwent balloon valvuloplasty (Queensland Children's Hospital, Brisbane) or surgical valvotomy (Royal Children's Hospital, Melbourne) between 2005 and 2016. Patients were excluded if pre-intervention assessment indicated ineligibility to either group. Propensity score matching was performed based on age, weight, and valve morphology. RESULTS: Sixty-five balloon patients and seventy-seven surgical patients were included. Overall, the groups were well matched with 18 neonates/25 infants in the balloon group and 17 neonates/28 infants in the surgical group. Median age at balloon was 92 days (range 2 days - 18.8 years) compared to 167 days (range 0 days - 18.1 years) for surgery (rank-sum p = 0.08). Mean follow-up was 5.3 years. There was one late balloon death and two early surgical deaths due to left ventricular failure. There was no significant difference in freedom from reintervention at latest follow-up (69% in the balloon group and 70% in the surgical group, p = 1.0). CONCLUSIONS: Contemporary analysis of balloon aortic valvuloplasty and surgical aortic valvotomy shows no difference in overall reintervention rates in the medium term. Balloon valvuloplasty performs well across all age groups, achieving delay or avoidance of surgical intervention.

Regulation of metabolism during hibernation in brown bears (Ursus arctos): Involvement of cortisol, PGC-1α and AMPK in adipose tissue and skeletal muscle.

The purpose of this study was to investigate changes in expression of known cellular regulators of metabolism during hyperphagia (Sept) and hibernation (Jan) in skeletal muscle and adipose tissue of brown bears and determine whether signaling molecules and transcription factors known to respond to changes in cellular energy state are involved in the regulation of these metabolic adaptations. During hibernation, serum levels of cortisol, glycerol, and triglycerides were elevated, and protein expression and activation of AMPK in skeletal muscle and adipose tissue were reduced. mRNA expression of the co-activator PGC-1α was reduced in all tissues in hibernation whereas mRNA expression of the transcription factor PPAR-α was reduced in the vastus lateralis muscle and adipose tissue only. During hibernation, gene expression of ATGL and CD36 was not altered; however, HSL gene expression was reduced in adipose tissue. During hibernation gene expression of the lipogenic enzyme DGAT in all tissues and the expression of the FA oxidative enzyme LCAD in the vastus lateralis muscle were reduced. Gene and protein expression of the glucose transporter GLUT4 was decreased in adipose tissue in hibernation. Our data suggest that high cortisol levels are a key adaptation during hibernation and link cortisol to a reduced activation of the AMPK/PGC-1α/PPAR-α axis in the regulation of metabolism in skeletal muscle and adipose tissue. Moreover, our results indicate that during this phase of hibernation at a time when metabolic rate is significantly reduced metabolic adaptations in peripheral tissues seek to limit the detrimental effects of unduly large energy dissipation.

Detection of a microbial metabolite by STING regulates inflammasome activation in response to Chlamydia trachomatis infection.

The innate immune system is a critical component of host defence against microbial pathogens, but effective responses require an ability to distinguish between infectious and non-infectious insult to prevent inappropriate inflammation. Using the important obligate intracellular human pathogen Chlamydia trachomatis; an organism that causes significant immunopathology, we sought to determine critical host and pathogen factors that contribute to the induction of inflammasome activation. We assayed inflammasome activation by immunoblotting and ELISA to detect IL-1ß processing and LDH release to determine pyroptosis. Using primary murine bone marrow derived macrophages or human monocyte derived dendritic cells, infected with live or attenuated Chlamydia trachomatis we report that the live organism activates both canonical and non-canonical inflammasomes, but only canonical inflammasomes controlled IL-1ß processing which preceded pyroptosis. NADPH oxidase deficient macrophages were permissive to Chlamydia trachomatis replication and displayed elevated type-1 interferon and inflammasome activation. Conversely, attenuated, non-replicating Chlamydia trachomatis, primed but did not activate inflammasomes and stimulated reduced type-1 interferon responses. This suggested bacterial replication or metabolism as important factors that determine interferon responses and inflammasome activation. We identified STING but not cGAS as a central mediator of interferon regulated inflammasome activation. Interestingly, exogenous delivery of a Chlamydia trachomatis metabolite and STING ligand-cyclic di-AMP, recovered inflammasome activation to attenuated bacteria in a STING dependent manner thus indicating that a bacterial metabolite is a key factor initiating inflammasome activation through STING, independent of cGAS. These data suggest a potential mechanism of how the innate immune system can distinguish between infectious and non-infectious insult and instigate appropriate immune responses that could be therapeutically targeted.

Metabolic derangements and reduced survival of bile-extracted Asiatic black bears (Ursus thibetanus).

BACKGROUND: Across China and Southeast Asia, an estimated 17,000 bears are currently farmed for bile, primarily for traditional medicines. Depending on country, bile is extracted daily via transabdominal gallbladder fistulas, indwelling catheters, or needle aspiration. Despite claims that bears do not develop adverse effects from bile extraction, health issues identified in bears removed from bile farms include bile-extraction site infections, abdominal hernias, peritonitis, cholecystitis, hepatic neoplasia, cardiac disease, skeletal abnormalities, and abnormal behaviors. We present a comprehensive assessment of the effects of bile farming by comparing serum biochemical and hematological values of bears from farms that were bile-extracted (BE) and bears from farms not bile-extracted (FNE) with bears from non-farm captive (ZOO) and free-range (FR) environments. We hypothesized BE bears would have significant laboratory abnormalities compared to all non-extracted bear groups. We also hypothesized BE bears would have reduced long-term survival compared to FNE bears despite removal from farms. RESULTS: BE bears exhibited the highest values and greatest variation (on a population level) in laboratory parameters compared to all non-extracted bear groups particularly for alanine transaminase, gamma glutamyltransferase (GGT), total bilirubin (TBIL), alkaline phosphatase (ALKP), blood urea nitrogen, creatinine (CREA), and total white blood cell count. Significant differences were detected between bear groups when accounting for season, sex, and/or age. BE bears exhibited greater mean serum GGT compared to all non-extracted bear groups, and the odds of having elevated TBIL were 7.3 times greater for BE bears, consistent with hepatobiliary disease. Biochemical parameter elevations in BE bears persisted up to 14 years post-rescue, consistent with long-term effects of bile-extraction. BE bears that arrived with elevated CREA and ALKP had median survival times of 1 and 4 years respectively, and regardless of laboratory abnormalities, BE bears had significantly shorter survival times compared to FNE bears. CONCLUSIONS: Our results provide strong evidence that bile extraction practices not only represent a temporary constraint for bears' welfare, but confer distinct long-term adverse health consequences. Routine laboratory panels may be insensitive to detect the extent of underlying illness in BE bears as these bears have significantly reduced survival regardless of biochemical assessment compared to FNE bears.

Subversion of innate immune responses by Francisella involves the disruption of TRAF3 and TRAF6 signalling complexes.

The success of pathogens depends on their ability to circumvent immune defences. Francisella tularensis is one of the most infectious bacteria known. The remarkable virulence of Francisella is believed to be due to its capacity to evade or subvert the immune system, but how remains obscure. Here, we show that Francisella triggers but concomitantly inhibits the Toll-like receptor, RIG-I-like receptor, and cytoplasmic DNA pathways. Francisella subverts these pathways at least in part by inhibiting K63-linked polyubiquitination and assembly of TRAF6 and TRAF3 complexes that control the transcriptional responses of pattern recognition receptors. We show that this mode of inhibition requires a functional type VI secretion system and/or the presence of live bacteria in the cytoplasm. The ability of Francisella to enter the cytosol while simultaneously inhibiting multiple pattern recognition receptor pathways may account for the notable capacity of this bacterium to invade and proliferate in the host without evoking a self-limiting innate immune response.

AORTIC ANEURYSM, DISSECTION, AND RUPTURE IN SIX BILE-FARMED BEARS.

Across China and Southeast Asia, over 17,000 bears are currently farmed for bile, predominantly for traditional Chinese medicines. Bears on farms in China are cage confined and undergo repeated daily bile extraction facilitated by surgically implanted catheters or gallbladder fistulas. Numerous health problems have been reported in bile-farmed bears including peritonitis, abdominal hernias, and extraction site abscessation. Between 2009 and 2014, five Asiatic black bears ( Ursus thibetanus) and one Asiatic black/Eurasian brown bear ( Ursus arctos arctos) hybrid, rescued from the bear bile industry in China, died from ruptured and/or dissecting aortic aneurysm. Medical records were reviewed and two bears exhibited no clinical signs prior to death. In four bears, clinical findings varied and included increased stereotypic behavior prior to death, epistaxis, retinal lesions, dysphagia, weight loss, and acute onset of hyporexia. On postmortem examination, hemopericardium with dissection and/or rupture of the ascending aorta and left ventricular wall hypertrophy were present in all cases. No evidence of infectious disease, connective tissue disorders, or congenital cardiac disease was identified. Based on these observations screening thoracic radiography was performed on all bears at the rescue center and aortic dilation was identified in 73 of 134 (54.5%) bile-extracted bears. To the authors' knowledge, aortic aneurysm, rupture, and/or dissection have not been previously reported in any bear species and the high prevalence in this population of bears suggests an association with bile-farming practices. Future studies are needed to investigate the etiopathogenesis of this condition to aid in early diagnosis and improved management of bears being rescued from bile farms across Asia.

Multimechanistic Monoclonal Antibodies (MAbs) Targeting Staphylococcus aureus Alpha-Toxin and Clumping Factor A: Activity and Efficacy Comparisons of a MAb Combination and an Engineered Bispecific Antibody Approach.

Secreted alpha-toxin and surface-localized clumping factor A (ClfA) are key virulence determinants in Staphylococcus aureus bloodstream infections. We previously demonstrated that prophylaxis with a multimechanistic monoclonal antibody (MAb) combination against alpha-toxin (MEDI4893*) and ClfA (11H10) provided greater strain coverage and improved efficacy in an S. aureus lethal bacteremia model. Subsequently, 11H10 was found to exhibit reduced affinity and impaired inhibition of fibrinogen binding to ClfA002 expressed by members of a predominant hospital-associated methicillin-resistant S. aureus (MRSA) clone, ST5. Consequently, we identified another anti-ClfA MAb (SAR114) from human tonsillar B cells with >100-fold increased affinity for three prominent ClfA variants, including ClfA002, and potent inhibition of bacterial agglutination by 112 diverse clinical isolates. We next constructed bispecific Abs (BiSAbs) comprised of 11H10 or SAR114 as IgG scaffolds and grafted anti-alpha-toxin (MEDI4893*) single-chain variable fragment to the amino or carboxy terminus of the anti-ClfA heavy chains. Although the BiSAbs exhibited in vitro potencies similar to those of the parental MAbs, only 11H10-BiSAb, but not SAR114-BiSAb, showed protective activity in murine infection models comparable to the respective MAb combination. In vivo activity with SAR114-BiSAb was observed in infection models with S. aureus lacking ClfA. Our data suggest that high-affinity binding to ClfA sequesters the SAR114-BiSAb to the bacterial surface, thereby reducing both alpha-toxin neutralization and protection in vivo These results indicate that a MAb combination targeting ClfA and alpha-toxin is more promising for future development than the corresponding BiSAb.

Grizzly bear (Ursus arctos horribilis) locomotion: forelimb joint mechanics across speed in the sagittal and frontal planes.

The majority of terrestrial locomotion studies have focused on parasagittal motion and paid less attention to forces or movement in the frontal plane. Our previous research has shown that grizzly bears produce higher medial ground reaction forces (lateral pushing from the animal) than would be expected for an upright mammal, suggesting frontal plane movement may be an important aspect of their locomotion. To examine this, we conducted an inverse dynamics analysis in the sagittal and frontal planes, using ground reaction forces and position data from three high-speed cameras of four adult female grizzly bears. Over the speed range collected, the bears used walks, running walks and canters. The scapulohumeral joint, wrist and the limb overall absorb energy (average total net work of the forelimb joints, -0.97 W kg-1). The scapulohumeral joint, elbow and total net work of the forelimb joints have negative relationships with speed, resulting in more energy absorbed by the forelimb at higher speeds (running walks and canters). The net joint moment and power curves maintain similar patterns across speed as in previously studied species, suggesting grizzly bears maintain similar joint dynamics to other mammalian quadrupeds. There is no significant relationship with net work and speed at any joint in the frontal plane. The total net work of the forelimb joints in the frontal plane was not significantly different from zero, suggesting that, despite the high medial ground reaction forces, the forelimb acts as a strut in that plane.