Robert P Rhoads | Virginia Tech (original) (raw)
Papers by Robert P Rhoads
Journal of Dairy Science, Jun 1, 2023
The FASEB Journal, Apr 1, 2016
Heat‐related complications continue to be a major health concern for humans and animals and lead ... more Heat‐related complications continue to be a major health concern for humans and animals and lead to potentially life‐threatening conditions ranging from heat exhaustion, heat stroke and even death. Heat stress have been shown to alter metabolic and energetic parameters in mammals and may alter glucose metabolism and insulin sensitivity. Therefore, the purpose of this investigation was to determine the extent to which short‐term HS altered markers of insulin signaling in oxidative skeletal muscle. To address this, crossbred gilts (n=8/group) were assigned to thermoneutral (TN; 24° C), HS (37° C), or pair‐fed to HS and kept under TN conditions (PFTN) groups for 12 hours. Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. HS‐induced changes were not caused by reduced feed intake as TN and PFTN were similar for nearly all measures. Twelve hours of HS increased insulin receptor protein abundance by 54% (p<0.05) and phosphorylated insulin receptor substrate (pIRS1S307) by 56% (p<0.05) compared to TN. Phosphorylation of IRS1 at this site is a negative regulator of insulin signaling. Relative protein abundance and phosphorylation of phosphoinositide 3‐kinase (PI3K) and 3‐phosphoinositide dependent protein kinase‐1 (PDK1) were similar between groups. Phosphorylation of protein kinase B (pAKTs473) was decreased by 53% (p<0.05) in HS compared to TN, which indicates that insulin signaling was suppressed through pIRS1. Conversely, HS increased phosphorylation of protein kinase C (PKC)λ/ζ and pPKCδ protein abundance by 128% and 205%, respectively, compared to TN which are known to stimulate pIRS1S307. Sarcolemma glucose transporter‐4 (Glut4) was decreased by 47% (p<0.05) in HS group compared to TN suggesting reduced glucose uptake. These data suggest that HS induces insulin sensititvity by disturbing insulin signaling via an AKT‐mediated pathway.Support or Funding InformationThis work is supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007
Journal of Animal Science, 2017
Journal of Animal Science, Jun 1, 2017
Journal of Animal Science, Dec 1, 2019
Heat stress continues to undermine efficient meat production and meat quality. It also jeopardize... more Heat stress continues to undermine efficient meat production and meat quality. It also jeopardizes human and animal health and wellbeing, regionalizes animal production, and threatens food security. Environmental models predict more frequent and severe heat waves, even in areas previously considered temperate indicating this problem will continue to have a progressively expanding, deleterious impact on agricultural productivity. Despite the broad, negative impact of heat stress little is known about underlying mechanisms leading to phenotypic outcomes. Because of its mass and energetic demands, skeletal muscle contributes greatly to regulation of systemic metabolism. We have discovered heat stress causes robust but transient oxidative stress and activation of apoptotic signaling in skeletal muscle in as little as two hours. Interestingly, these declined linearly through six hours concomitant with markers of increased autophagy and mitophagy, which would facilitate the removal of damaged mitochondria. Continued heating through 24 h causes a resumption of oxidative stress and autophagic dysfunction with an accumulation of autophagosomes and mitochondria. As mitochondrial injury and autophagic dysregulation appear to be key mediators of hyperthermic muscle dysfunction we propose a model that posits progressive mitochondrial injury leads to production of free radicals that overwhelms antioxidant systems and impairs autophagy facilitating accumulation of damaged, pro-oxidant mitochondria. Ultimately, these aforementioned changes may reduce efficient protein accretion. Our current work is focused on stimulating autophagy and protecting mitochondria during heat stress in an effort to maintain efficient muscle growth.
Journal of Animal Science, Sep 1, 2015
The FASEB Journal, Apr 1, 2016
We have previously reported that 24 hours of heat stress (HS) induced free radical injury in oxid... more We have previously reported that 24 hours of heat stress (HS) induced free radical injury in oxidative skeletal muscle. In addition, we found widespread aberrant intracellular signaling following 12h of HS. The aim of this investigation was to extend our knowledge regarding the early chronology of HS‐mediated intracellular signalling in oxidative skeletal muscle. We hypothesized that 2, 4, and 6 hours of HS would result in increased autophagy and decreased mitochondrial content in oxidative skeletal muscle compared to muscle maintained under thermoneutral (TN) conditions. To address this hypothesis, pigs were assigned to four groups (n=8/group) and housed under TN conditions (21°C) or exposed to HS (37°C) for 2, 4, or 6 hours. Next, animals were euthanized and the semitendinosus red (STR) was collected and analyzed. Compared to TN, relative protein abundance of autophagy initiators phosphoinositide 3‐kinase Class III and Beclin‐1 were increased by 57% and 56%, respectively (p<0.05), following 6 hours of HS. At the same time point, relative abundance of the pre‐autophagosomal structure stabilizer, autophagy‐related protein 16‐1 (ATG16), was increased 59% (p<0.05). Microtubule‐associated protein A/B light chain 3 (LC3)‐I was similar between all four groups but the autophagosome formation marker LC3‐II was increased by 94% (p<0.05) following 6 hours of HS compared to TN. This resulted in a 2‐fold increase in the LC3II/I ratio (p<0.05), which is indicative of increased autophagic flux, though sequstome‐1 (p62) protein abundance was similar between groups. In addition, the mitophagy marker, BCL2/adenovirus E1B protein‐interacting protein 3‐like (BNIP3), was increased by 41% (p<0.05) following 6 hours of HS compared to TN. Relative protein abundance of TCA enzymes, electron transport chain components, and mitochondrial markers was similar between groups. These data demonstrate that short‐term HS induced autophagy/mitophagy. Together with our previous work we also suggest thatbetween 6 and 12 hours of HS the intracellular environment of oxidative skeletal muscle switches from one that promotes autophagy to one that inhibits it.Support or Funding InformationThis work supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007.
The FASEB Journal, Apr 1, 2012
The FASEB Journal, Apr 1, 2016
Prolonged exposure to high temperatures can result in heat stress (HS), which is characterized by... more Prolonged exposure to high temperatures can result in heat stress (HS), which is characterized by morbidities and mortality in humans and animals and appears to cause organ‐specific injury and dysfunction. We have previously found increased free radical injury in skeletal muscle following 24 hours of HS. The purpose of this investigation was to determine the extent to which short‐term HS caused muscle dysfunction in oxidative skeletal muscle. We hypothesized that in oxidative muscle 12 hours of HS would lead to free radical injury, apoptosis, autophagy, and decreased mitochondrial content compared to muscle from thermoneutral (TN) animals. To address this hypothesis, crossbred gilts (n=8/group) were assigned to three groups: TN (24° C), HS (37° C), or pair‐fed to heat stress (PFTN; 24° C) for 12 hours. Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. TN and PFTN were similar for nearly all measures indicating changes caused by HS were not due to reduced feed intake but due to the hyperthermic environment. The relative abundance of malondialdehyde modified proteins was increased by 36% in HS (p<0.05) compared to TN, which was matched by an inadequate antioxidant response including a 48% and 170% increase in superoxide dismutase (SOD) I and II relative protein abundance, respectively, and a 26% increase in total SOD activity but a 40% reduction in catalase activity in HS compared to TN. Further, HS caused a 103% increase in caspase 3 activation and tended to increase BCL2‐Associated X Protein by 40% (p<0.06) and apoptotic protease activating factor 1 by 66% (p<0.06) indicating increased apoptotic signaling. Despite increased initiation, autophagy appeared to be inhibited by HS as the microtubule‐associated protein A/B‐light chain 3 II/I ratio was decreased by 53% and sequestosome‐1(p62) protein abundance was increased by 40% in HS compared to TN. Markers of mitochondrial content cytochrome c, cytochrome c oxidase IV, voltage dependent anion channel, pyruvate dehydrogenase and prohibitins 1 were increased in HS compared to TN. Increased mitochondrial content is likely reflective of a combination of increased accumulation of damaged mitochondria that fail to be cleared via autophagy and mitochondrial biogenesis. We postulate that in oxidative skeletal muscle HS‐mediated mitochondrial dysfunction is allowed to persist due to a failure of autophagy to clear damaged mitochondria, which results in increased oxidative stress and apoptotic signaling. These data demonstrate widespread aberrant intracellular signaling caused by HS that implicate impaired autophagy as a key feature in HS‐mediated muscle dysfunctionSupport or Funding InformationThis work supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007.
Journal of Thermal Biology
Heat stress (HS) poses a major threat to human health and agricultural production. Oxidative stre... more Heat stress (HS) poses a major threat to human health and agricultural production. Oxidative stress and mitochondrial dysfunction appear to play key roles in muscle injury caused by HS. We hypothesized that mitoquinol (MitoQ), would alleviate oxidative stress and cellular dysfunction in skeletal muscle during HS. To address this, crossbred barrows (male pigs) were treated with placebo or MitoQ (40 mg/d) and were then exposed to thermoneutral (TN; 20 °C) or HS (35 °C) conditions for 24 h. Pigs were euthanized following the environmental challenge and the red portion of the semitendinosus (STR) was collected for analysis. Unexpectedly, malondialdehyde concentration, an oxidative stress marker, was similar between environmental and supplement treatments. Heat stress decreased LC3A/B-I (p < 0.05) and increased the ratio of LC3A/B-II/I (p < 0.05), while p62 was similar among groups suggesting increased degradation of autophagosomes during HS. These outcomes were in disagreement with our previous results in muscle from gilts (female pigs). To probe the impact of biological sex on HS-mediated injury in skeletal muscle, we compared STR from these barrows to archived STR from gilts subjected to a similar environmental intervention. We confirmed our previous findings of HS-mediated dysfunction in muscle from gilts but not barrows. These data also raise the possibility that muscle from gilts is more susceptible to environment-induced hyperthermia than muscle from barrows.
The FASEB Journal, 2015
Hyperthermic pigs differ metabolically, including altered insulin profiles, reduced lipolysis, an... more Hyperthermic pigs differ metabolically, including altered insulin profiles, reduced lipolysis, and compromised intestinal integrity, leading to lower lean tissue and elevated adipose tissue mass. T...
AFMA Matrix, 2016
There is a variety of conditions in a farm animal's life when nutrient utilisation is priorit... more There is a variety of conditions in a farm animal's life when nutrient utilisation is prioritised towards agriculturally unproductive purposes. Two well-known examples that markedly reduce production efficiency are heat stress and ketosis. Decreased feed intake, experienced in both cases, is unable to fully account for decreased productivity. In addition, both ketosis and heat stress are characterised by a negative energy balance, body weight loss, inflammation and hepatic steatosis.
Journal of Dairy Science, 2020
The FASEB Journal, 2020
Heat stress (HS) alters animal metabolism causing reduced performance (muscle growth) while incre... more Heat stress (HS) alters animal metabolism causing reduced performance (muscle growth) while increasing the incidence of disease and mortality. HS is particularly detrimental in the swine industry where the global economic burden of heat stress is in the billions of dollars annually. Excess environmental heat promotes a HS response increasing the expression of heat shock factors and heat shock proteins which coordinate a shift in metabolic substrate preference. The net result of these changes is a metabolic phenotype with limited lipid oxidation that relies on aerobic and anaerobic glycolysis as a predominant source of energy production. This study was designed to evaluate the effect of HS on substrate utilization and overall animal metabolic rate in growing pigs. Crossbred barrows (15.2±2.4 kg) were exposed to 5 days of TN (thermal neutral, 24 C°) or HS ( 35 C°) (n=8 per treatment), after a 5‐day acclimation period (24 C°). Pigs were fed ad libitum and monitored regularly for respir...
Journal of Dairy Science, Jun 1, 2023
The FASEB Journal, Apr 1, 2016
Heat‐related complications continue to be a major health concern for humans and animals and lead ... more Heat‐related complications continue to be a major health concern for humans and animals and lead to potentially life‐threatening conditions ranging from heat exhaustion, heat stroke and even death. Heat stress have been shown to alter metabolic and energetic parameters in mammals and may alter glucose metabolism and insulin sensitivity. Therefore, the purpose of this investigation was to determine the extent to which short‐term HS altered markers of insulin signaling in oxidative skeletal muscle. To address this, crossbred gilts (n=8/group) were assigned to thermoneutral (TN; 24° C), HS (37° C), or pair‐fed to HS and kept under TN conditions (PFTN) groups for 12 hours. Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. HS‐induced changes were not caused by reduced feed intake as TN and PFTN were similar for nearly all measures. Twelve hours of HS increased insulin receptor protein abundance by 54% (p<0.05) and phosphorylated insulin receptor substrate (pIRS1S307) by 56% (p<0.05) compared to TN. Phosphorylation of IRS1 at this site is a negative regulator of insulin signaling. Relative protein abundance and phosphorylation of phosphoinositide 3‐kinase (PI3K) and 3‐phosphoinositide dependent protein kinase‐1 (PDK1) were similar between groups. Phosphorylation of protein kinase B (pAKTs473) was decreased by 53% (p<0.05) in HS compared to TN, which indicates that insulin signaling was suppressed through pIRS1. Conversely, HS increased phosphorylation of protein kinase C (PKC)λ/ζ and pPKCδ protein abundance by 128% and 205%, respectively, compared to TN which are known to stimulate pIRS1S307. Sarcolemma glucose transporter‐4 (Glut4) was decreased by 47% (p<0.05) in HS group compared to TN suggesting reduced glucose uptake. These data suggest that HS induces insulin sensititvity by disturbing insulin signaling via an AKT‐mediated pathway.Support or Funding InformationThis work is supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007
Journal of Animal Science, 2017
Journal of Animal Science, Jun 1, 2017
Journal of Animal Science, Dec 1, 2019
Heat stress continues to undermine efficient meat production and meat quality. It also jeopardize... more Heat stress continues to undermine efficient meat production and meat quality. It also jeopardizes human and animal health and wellbeing, regionalizes animal production, and threatens food security. Environmental models predict more frequent and severe heat waves, even in areas previously considered temperate indicating this problem will continue to have a progressively expanding, deleterious impact on agricultural productivity. Despite the broad, negative impact of heat stress little is known about underlying mechanisms leading to phenotypic outcomes. Because of its mass and energetic demands, skeletal muscle contributes greatly to regulation of systemic metabolism. We have discovered heat stress causes robust but transient oxidative stress and activation of apoptotic signaling in skeletal muscle in as little as two hours. Interestingly, these declined linearly through six hours concomitant with markers of increased autophagy and mitophagy, which would facilitate the removal of damaged mitochondria. Continued heating through 24 h causes a resumption of oxidative stress and autophagic dysfunction with an accumulation of autophagosomes and mitochondria. As mitochondrial injury and autophagic dysregulation appear to be key mediators of hyperthermic muscle dysfunction we propose a model that posits progressive mitochondrial injury leads to production of free radicals that overwhelms antioxidant systems and impairs autophagy facilitating accumulation of damaged, pro-oxidant mitochondria. Ultimately, these aforementioned changes may reduce efficient protein accretion. Our current work is focused on stimulating autophagy and protecting mitochondria during heat stress in an effort to maintain efficient muscle growth.
Journal of Animal Science, Sep 1, 2015
The FASEB Journal, Apr 1, 2016
We have previously reported that 24 hours of heat stress (HS) induced free radical injury in oxid... more We have previously reported that 24 hours of heat stress (HS) induced free radical injury in oxidative skeletal muscle. In addition, we found widespread aberrant intracellular signaling following 12h of HS. The aim of this investigation was to extend our knowledge regarding the early chronology of HS‐mediated intracellular signalling in oxidative skeletal muscle. We hypothesized that 2, 4, and 6 hours of HS would result in increased autophagy and decreased mitochondrial content in oxidative skeletal muscle compared to muscle maintained under thermoneutral (TN) conditions. To address this hypothesis, pigs were assigned to four groups (n=8/group) and housed under TN conditions (21°C) or exposed to HS (37°C) for 2, 4, or 6 hours. Next, animals were euthanized and the semitendinosus red (STR) was collected and analyzed. Compared to TN, relative protein abundance of autophagy initiators phosphoinositide 3‐kinase Class III and Beclin‐1 were increased by 57% and 56%, respectively (p<0.05), following 6 hours of HS. At the same time point, relative abundance of the pre‐autophagosomal structure stabilizer, autophagy‐related protein 16‐1 (ATG16), was increased 59% (p<0.05). Microtubule‐associated protein A/B light chain 3 (LC3)‐I was similar between all four groups but the autophagosome formation marker LC3‐II was increased by 94% (p<0.05) following 6 hours of HS compared to TN. This resulted in a 2‐fold increase in the LC3II/I ratio (p<0.05), which is indicative of increased autophagic flux, though sequstome‐1 (p62) protein abundance was similar between groups. In addition, the mitophagy marker, BCL2/adenovirus E1B protein‐interacting protein 3‐like (BNIP3), was increased by 41% (p<0.05) following 6 hours of HS compared to TN. Relative protein abundance of TCA enzymes, electron transport chain components, and mitochondrial markers was similar between groups. These data demonstrate that short‐term HS induced autophagy/mitophagy. Together with our previous work we also suggest thatbetween 6 and 12 hours of HS the intracellular environment of oxidative skeletal muscle switches from one that promotes autophagy to one that inhibits it.Support or Funding InformationThis work supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007.
The FASEB Journal, Apr 1, 2012
The FASEB Journal, Apr 1, 2016
Prolonged exposure to high temperatures can result in heat stress (HS), which is characterized by... more Prolonged exposure to high temperatures can result in heat stress (HS), which is characterized by morbidities and mortality in humans and animals and appears to cause organ‐specific injury and dysfunction. We have previously found increased free radical injury in skeletal muscle following 24 hours of HS. The purpose of this investigation was to determine the extent to which short‐term HS caused muscle dysfunction in oxidative skeletal muscle. We hypothesized that in oxidative muscle 12 hours of HS would lead to free radical injury, apoptosis, autophagy, and decreased mitochondrial content compared to muscle from thermoneutral (TN) animals. To address this hypothesis, crossbred gilts (n=8/group) were assigned to three groups: TN (24° C), HS (37° C), or pair‐fed to heat stress (PFTN; 24° C) for 12 hours. Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. TN and PFTN were similar for nearly all measures indicating changes caused by HS were not due to reduced feed intake but due to the hyperthermic environment. The relative abundance of malondialdehyde modified proteins was increased by 36% in HS (p<0.05) compared to TN, which was matched by an inadequate antioxidant response including a 48% and 170% increase in superoxide dismutase (SOD) I and II relative protein abundance, respectively, and a 26% increase in total SOD activity but a 40% reduction in catalase activity in HS compared to TN. Further, HS caused a 103% increase in caspase 3 activation and tended to increase BCL2‐Associated X Protein by 40% (p<0.06) and apoptotic protease activating factor 1 by 66% (p<0.06) indicating increased apoptotic signaling. Despite increased initiation, autophagy appeared to be inhibited by HS as the microtubule‐associated protein A/B‐light chain 3 II/I ratio was decreased by 53% and sequestosome‐1(p62) protein abundance was increased by 40% in HS compared to TN. Markers of mitochondrial content cytochrome c, cytochrome c oxidase IV, voltage dependent anion channel, pyruvate dehydrogenase and prohibitins 1 were increased in HS compared to TN. Increased mitochondrial content is likely reflective of a combination of increased accumulation of damaged mitochondria that fail to be cleared via autophagy and mitochondrial biogenesis. We postulate that in oxidative skeletal muscle HS‐mediated mitochondrial dysfunction is allowed to persist due to a failure of autophagy to clear damaged mitochondria, which results in increased oxidative stress and apoptotic signaling. These data demonstrate widespread aberrant intracellular signaling caused by HS that implicate impaired autophagy as a key feature in HS‐mediated muscle dysfunctionSupport or Funding InformationThis work supported by USDA grants 2014‐67015‐21627 and 2011‐67003‐30007.
Journal of Thermal Biology
Heat stress (HS) poses a major threat to human health and agricultural production. Oxidative stre... more Heat stress (HS) poses a major threat to human health and agricultural production. Oxidative stress and mitochondrial dysfunction appear to play key roles in muscle injury caused by HS. We hypothesized that mitoquinol (MitoQ), would alleviate oxidative stress and cellular dysfunction in skeletal muscle during HS. To address this, crossbred barrows (male pigs) were treated with placebo or MitoQ (40 mg/d) and were then exposed to thermoneutral (TN; 20 °C) or HS (35 °C) conditions for 24 h. Pigs were euthanized following the environmental challenge and the red portion of the semitendinosus (STR) was collected for analysis. Unexpectedly, malondialdehyde concentration, an oxidative stress marker, was similar between environmental and supplement treatments. Heat stress decreased LC3A/B-I (p < 0.05) and increased the ratio of LC3A/B-II/I (p < 0.05), while p62 was similar among groups suggesting increased degradation of autophagosomes during HS. These outcomes were in disagreement with our previous results in muscle from gilts (female pigs). To probe the impact of biological sex on HS-mediated injury in skeletal muscle, we compared STR from these barrows to archived STR from gilts subjected to a similar environmental intervention. We confirmed our previous findings of HS-mediated dysfunction in muscle from gilts but not barrows. These data also raise the possibility that muscle from gilts is more susceptible to environment-induced hyperthermia than muscle from barrows.
The FASEB Journal, 2015
Hyperthermic pigs differ metabolically, including altered insulin profiles, reduced lipolysis, an... more Hyperthermic pigs differ metabolically, including altered insulin profiles, reduced lipolysis, and compromised intestinal integrity, leading to lower lean tissue and elevated adipose tissue mass. T...
AFMA Matrix, 2016
There is a variety of conditions in a farm animal's life when nutrient utilisation is priorit... more There is a variety of conditions in a farm animal's life when nutrient utilisation is prioritised towards agriculturally unproductive purposes. Two well-known examples that markedly reduce production efficiency are heat stress and ketosis. Decreased feed intake, experienced in both cases, is unable to fully account for decreased productivity. In addition, both ketosis and heat stress are characterised by a negative energy balance, body weight loss, inflammation and hepatic steatosis.
Journal of Dairy Science, 2020
The FASEB Journal, 2020
Heat stress (HS) alters animal metabolism causing reduced performance (muscle growth) while incre... more Heat stress (HS) alters animal metabolism causing reduced performance (muscle growth) while increasing the incidence of disease and mortality. HS is particularly detrimental in the swine industry where the global economic burden of heat stress is in the billions of dollars annually. Excess environmental heat promotes a HS response increasing the expression of heat shock factors and heat shock proteins which coordinate a shift in metabolic substrate preference. The net result of these changes is a metabolic phenotype with limited lipid oxidation that relies on aerobic and anaerobic glycolysis as a predominant source of energy production. This study was designed to evaluate the effect of HS on substrate utilization and overall animal metabolic rate in growing pigs. Crossbred barrows (15.2±2.4 kg) were exposed to 5 days of TN (thermal neutral, 24 C°) or HS ( 35 C°) (n=8 per treatment), after a 5‐day acclimation period (24 C°). Pigs were fed ad libitum and monitored regularly for respir...