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ABSTRACT: Exaggerated proinflammatory cytokine responses can be observed with aging, and reduced levels of the anti-inflammatory cytokine IL-10 may contribute to these responses. IL-10 can reduce IL-6, IL-1beta, and TNF-alpha expression in nonmuscle tissues; however, no studies have examined the combined effects of IL-10 and age on cytokine responses in skeletal and cardiac muscle. These experiments tested the hypothesis that the absence of IL-10, in vivo, is associated with greater IL-6, TNF-alpha, and IL-1beta responses to an inflammatory challenge in skeletal and cardiac muscle and that aging exaggerates these responses. We compared IL-6, IL-1beta, and TNF-alpha mRNA and protein levels in skeletal and cardiac muscle of young (4 mo) and mature (10-11 mo) wild-type (IL-10(+/+)) and IL-10 deficient (IL-10(-/-)) mice following LPS. Skeletal and cardiac IL-6 mRNA and protein were elevated by LPS for IL-10(+/+) and IL-10(-/-) mice with greater responses in the IL-10(-/-) mice (P < 0.01). In skeletal muscle these effects were greater in mature than young mice (P < 0.01). IL-1beta mRNA and protein responses to LPS were greater in cardiac muscle of young but not mature IL-10(-/-) mice compared with IL-10(+/+) (P < 0.01). However, IL-1beta responses were greater in mature than young mice, but only in IL-10(+/+) groups (P < 0.05). The absence of IL-10 was associated with higher TNF-alpha protein levels in cardiac muscle (P < 0.05). The results provide the first in vivo evidence that the absence of IL-10 is associated with a greater IL-6 response to LPS in skeletal and cardiac muscles, and in skeletal muscle aging further exaggerates these responses.
Journal of Applied Physiology 05/2008; 104(4):991-7. · 3.75 Impact Factor
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ABSTRACT: Previous reports suggest a role for neuromuscular activity levels and/or connectivity in modulating Hsp25 expression and phosphorylation (pHsp25) in skeletal muscles. However, pHsp25 has only been studied in denervated muscles and/or muscles exposed to high levels of residual neuromuscular activity. Spinal cord isolation (SI) provides a model in which the muscle is exposed to nearly complete inactivity with maintenance of the nerve-muscle connection. To parcel out the roles of innervation state and activity-independent neural factors, we compared Hsp25 and pHsp25 in the plantaris of control (Con), SI, and denervated (Den, inactivity without neural connectivity) rats.
Hsp25 and pHsp25 protein levels (soluble and insoluble fractions) were measured with Western blot analysis after 1, 3, 8, 14, or 28 days of SI or Den. pHsp25 was normalized to non-pHsp25 at each time point.
Hsp25 was unchanged (days 1, 3 and 14) or increased (days 8 and 28) in the soluble fraction, and decreased (day 1) or increased (days 3, 8 and 14) in the insoluble fraction in Den compared with Con rats. pHsp25 was reduced after 1 and 28 days of Den, but near control levels on days 3, 8, and 14 in the soluble fraction. In the insoluble fraction, pHsp25 levels were lower in Den than Con rats on all days. In both fractions, Hsp25 was lower in SI than Con rats. pHsp25 levels were lower in the soluble fraction and higher in the insoluble fraction in SI than Con rats.
These results suggest that an intact innervation, even in the absence of muscle activation and/or loading, is critical for Hsp25 phosphorylation in the insoluble fraction. However, the time-dependent decrease in Hsp25 with SI suggests a role for minimal levels of muscle activation and/or loading in maintaining Hsp25 expression during sustained inactivity.
Acta Physiologica Scandinavica 12/2005; 185(3):219-27. · 2.55 Impact Factor
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ABSTRACT: Data supporting the hypothesis that dopamine-2 receptors (D(2)-R) contribute to time-dependent changes in the hypoxic ventilatory response (HVR) during acclimatization to hypoxia are briefly reviewed. Previous experiments with transgenic animals (D(2)-R 'knockout' mice) support this hypothesis (J. Appl. Physiol. 89 (2000) 1142). However, those experiments could not determine (1) if D(2)-R in the carotid body, the CNS, or both were involved, or (2) if D(2)-R were necessary during the acclimatization to hypoxia versus some time prior to chronic hypoxia, e.g. during a critical period of development. Additional experiments on C57BL/6J mice support the idea that D(2)-R are critical during the period of exposure to hypoxia for normal ventilatory acclimatization. D(2)-R in carotid body chemoreceptors predominate under control conditions to inhibit normoxic ventilation, but excitatory effects of D(2)-R, presumably in the CNS, predominate after acclimatization to hypoxia. The inhibitory effects of D(2)-R in the carotid body are reset to operate primarily under hypoxic conditions in acclimatized rats, thereby optimizing O(2)-sensitivity.
Respiratory Physiology & Neurobiology 06/2003; 135(2-3):133-44. · 2.24 Impact Factor
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ABSTRACT: Denervation (DEN) of rat soleus is associated with a decreased expression of slow type I myosin heavy chain (MHC) and an increased expression of the faster MHC isoforms. The molecular mechanisms behind these shifts remain unclear. We first investigated endogenous transcriptional activity of the type I MHC gene in normal and denervated soleus muscles via pre-mRNA analysis. Our results suggest that the type I MHC gene is regulated via transcriptional processes in the denervated soleus. Deletion and mutational analysis of the rat type I MHC promoter was then used to identify cis elements or regions of the promoter involved in this response. DEN significantly decreased in vivo activity of the -3,500, -2,500, -914, -408, -299, and -215 bp type I MHC promoters, relative to the alpha-skeletal actin promoter. In contrast, normalized -171 promoter activity was unchanged. Mutation of the betae3 element (-214/-190) in the -215 promoter and deletion of this element (-171 promoter) blunted type I downregulation with DEN. In contrast, betae3 mutation in the -408 promoters was not effective in attenuating the DEN response, suggesting the existence of additional DEN-responsive sites between -408 and -215. Western blotting and gel mobility supershift assays demonstrated decreased expression and DNA binding of transcription enhancer factor 1 (TEF-1) with DEN, suggesting that this decrease may contribute to type I MHC downregulation in denervated muscle.
AJP Cell Physiology 04/2003; 284(3):C738-48. · 3.54 Impact Factor
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ABSTRACT: Chronic muscle inactivity with spinal cord isolation (SI) decreases expression of slow type I myosin heavy chain (MHC) while increasing expression of the faster MHC isoforms, primarily IIx. The purpose of this study was to determine whether type I MHC downregulation in the soleus muscle of SI rats is regulated transcriptionally and to identify cis-acting elements or regions of the rat type I MHC gene promoter involved in this response. One week of SI significantly decreased in vivo activity of the -3500-, -408-, -299-, -215-, and -171-bp type I MHC promoters. The activity of all tested deletions of the type I MHC promoter, relative to the human skeletal alpha-actin promoter, were significantly reduced in the SI soleus, except activity of the -171-bp promoter, which increased. Mutation of the betae3 element (-214/-190 bp) in the -215- and -408-bp promoters and deletion of this element (-171-bp promoter) attenuated type I downregulation with SI. Gel mobility shift assays demonstrated a decrease in transcription enhancer factor-1 binding to the betae3 element with SI, despite an increase in total binding to this region. These results demonstrate that type I MHC downregulation with SI is transcriptionally regulated and suggest that interactions between transcription enhancer factor-1 and the betae3 element are likely involved in this response.
AJP Cell Physiology 04/2002; 282(3):C528-37. · 3.54 Impact Factor
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ABSTRACT: Myosin heavy chain (MHC) mRNA and protein profiles in adult rat soleus and adductor longus were determined after 4, 8, 15, 30, 60, and 90 days of spinal cord isolation (SI). SI results in complete neuromuscular inactivity while leaving the motoneuron-muscle fiber connections intact. From 15 to 90 days, type I MHC mRNA was significantly decreased, whereas type I MHC protein did not significantly decrease until 30 and 60 days in the soleus and adductor longus, respectively. However, in both muscles, slow MHC downregulation was offset by significant upregulation of the faster MHC isoforms, primarily IIx. From 60 to 90 days, type I MHC was almost completely replaced with faster isoforms at the mRNA and protein levels. Thus, chronic inactivity and unloading of slow rat hindlimb muscles shifted the MHC profile from predominately type I to type IIx MHC mRNA and protein.
Muscle & Nerve 05/2001; 24(4):517-26. · 2.37 Impact Factor
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ABSTRACT: Modulation of the hypoxic ventilatory response (HVR) by dopamine D(2)-receptors (D(2)-R) in the carotid body (CB) and central nervous system (CNS) are hypothesized to contribute to ventilatory acclimatization to hypoxia. We tested this with blockade of D(2)-R in the CB or CNS in conscious rats after 0, 2 and 8 days of hypoxia. On day 0, CB D(2)-R blockade significantly increased VI and frequency (fR) in hyperoxia (FI(O(2))=0.30), but not hypoxia (FI(O(2))=0.10). CNS D(2)-R blockade significantly decreased fR in hypoxia only. On day 2, neither CB nor CNS D(2)-R blockade affected VI or fR. On day 8, CB D(2)-R blockade significantly increased hypoxic VI and fR. CNS D(2)-R blockade significantly decreased hypoxic VI and fR. CB and CNS D(2)-R modulation of the HVR decreased after 2 days of hypoxia, but reappeared after 8 days. Changes in the opposing effects of CB and CNS D(2)-R on the HVR during chronic hypoxia cannot completely explain ventilatory acclimatization in rats.
Respiration Physiology 12/2000; 123(3):177-87.
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ABSTRACT: We used genetically engineered D(2) receptor-deficient [D(2)-(-/-)] and wild-type [D(2)-(+/+)] mice to test the hypothesis that dopamine D(2) receptors modulate the ventilatory response to acute hypoxia [hypoxic ventilatory response (HVR)] and hypercapnia [hypercapnic ventilatory response (HCVR)] and time-dependent changes in ventilation during chronic hypoxia. HVR was independent of gender in D(2)-(+/+) mice and significantly greater in D(2)-(-/-) than in D(2)-(+/+) female mice. HCVR was significantly greater in female D(2)-(+/+) mice than in male D(2)-(+/+) and was greater in D(2)-(-/-) male mice than in D(2)-(+/+) male mice. Exposure to hypoxia for 2-8 days was studied in male mice only. D(2)-(+/+) mice showed time-dependent increases in "baseline" ventilation (inspired PO(2) = 214 Torr) and hypoxic stimulated ventilation (inspired PO(2) = 70 Torr) after 8 days of acclimatization to hypoxia, but D(2)-(-/-) mice did not. Hence, dopamine D(2) receptors modulate the acute HVR and HCVR in mice in a gender-specific manner and contribute to time-dependent changes in ventilation and the acute HVR during acclimatization to hypoxia.
Journal of Applied Physiology 10/2000; 89(3):1142-50. · 3.75 Impact Factor
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ABSTRACT: Ventilatory acclimatization to hypoxia is the time-dependent increase in ventilation that occurs with chronic exposure to hypoxia. Despite decades of research, the physiological mechanisms that increase the hypoxic ventilatory response during chronic hypoxia are not well understood. This review focuses on adaptations within the central nervous system (CNS) that increase the hypoxic ventilatory response. Although an increase in CNS responsiveness had been proposed many years ago, only recently has strong experimental evidence been provided for an increase in the CNS gain in the rat, which has proved to be a good model of VAH in humans. Within the CNS, several neuroanatomical sites could be involved as well as changes in various neurotransmitters, neuromodulators or signalling mechanisms within any of those sites. Lastly, adaptations within the CNS could involve both direct effects of decreased P(O(2)) and indirect effects of increased afferent nerve activity due to chronic stimulation of the peripheral arterial chemoreceptors.
Respiration Physiology 08/2000; 121(2-3):223-36.
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ABSTRACT: The hypoxic ventilatory response (HVR) can be modulated by dopamine D(2)-receptors (D(2)-R) in both the carotid body arterial chemoreceptors and the nucleus tractus solitarius (NTS), the primary synapse site of carotid body afferents. We hypothesized that chronic hypoxia alters D(2)-R gene expression to initiate changes in D(2)-R modulation of the HVR and enhance ventilatory acclimatization to hypoxia. Thus, we used a competitive reverse transcription-polymerase chain reaction (RT-PCR) method to quantify changes in D(2)-R mRNA levels in the rat carotid body and NTS after 0, 6, 12, 24, 48, or 168 h of hypobaric hypoxia (P(IO(2))=80 Torr). In the rostral NTS, hypoxia significantly increased D(2)-R mRNA at all time points. In the caudal NTS, D(2)-R mRNA levels initially increased in response to hypoxia and then significantly decreased to 71+/-5% and 71+/-6% of control after 48 and 168 h of hypoxia, respectively. In the carotid body, D(2)-R mRNA levels significantly decreased to 59+/-2% of control after 48 h of hypoxia; however, they significantly increased to 274+/-22% of control after 168 h. These results suggest that changes in D(2)-R mRNA in the arterial chemoreflex pathway and corresponding changes at the protein and signaling levels may contribute to the time-dependent changes in ventilation observed with chronic hypoxia. Specifically, decreased carotid body inhibition by D(2)-R could increase the HVR after 2 days of hypoxia.
Molecular Brain Research 03/2000; 75(2):264-70. · 2.00 Impact Factor
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ABSTRACT: Chronic hypoxia increases the hypoxic ventilatory response (HVR) in awake rats and the phrenic nerve response to carotid sinus nerve stimulation in anesthetized rats. An increased O2 sensitivity of the arterial chemoreceptors contributes to the increase in the HVR, but changes in the CNS processing of afferent information from arterial chemoreceptors are also involved. Adult male Sprague-Dawley rats were exposed to 0-7 days of hypobaric hypoxia (PIO2 = 80 Torr). Ventilation was measured in rats exposed to 0, 2 and 7 days of hypoxia using whole-body plethysmography. Ventilation increased after 2 days and remained elevated after 7 days of hypoxia. Following dopamine D2 receptor (D2-R) blockade in the CNS, frequency significantly decreased after 0 and 7 days of hypoxia, but did not change significantly after 2 days of hypoxia. In anesthetized rats, the phrenic nerve response to carotid sinus nerve stimulation was reduced following systemic D2-R blockade in control rats and those exposed to 7 days of hypoxia. After 2 days of hypoxia, there was no effect of blocking systemic D2-R. To determine whether changes in D2-R mRNA precede physiological changes, competitive RT-PCR was used to quantify D2-R mRNA in micropunches from the nucleus tractus solitarius (NTS) in normoxic and chronically hypoxic rats. In hypoxia, D2-R mRNA in the caudal NTS initially increased (6-12 hours) and then decreased below control levels (24 hours-7 days). These results show that chronic hypoxia causes time-dependent changes in D2-R that could result in changes in the ventilatory response to hypoxia.
Advances in experimental medicine and biology 02/2000; 475:477-84. · 1.09 Impact Factor
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ABSTRACT: Denervation differs from other models of reduced neuromuscular activation due to the absence of a nerve-muscle connection and limited data exists regarding the effects of denervation on myosin heavy chain (MHC) expression. Thus, adult MHC expression (I, IIa, IIx, IIb) was studied in the rat soleus and tibialis anterior (TA) at the mRNA and protein levels 2, 4, 7, 10, 14, and 30 days following sciatic nerve transection. MHC protein content was quantified with SDS/PAGE and mRNA levels with the RNase-protection assay. Control soleus consisted predominately of type I MHC mRNA and protein, however, 4 days after denervation type I MHC mRNA was significantly decreased to 41+/-8% of control and continued to remain below control values. Soleus IIa mRNA was significantly elevated 7 and 10 days after denervation while IIx mRNA remained relatively constant until 30 days when it increased to 197+/-23% of control. At the protein level, soleus I MHC significantly decreased to 80% of the total while IIa MHC significantly increased to 20% of the total. At 30 days, Hx MHC protein accounted for 9.4+/-1.6% of the total soleus MHC protein. In the TA, IIb mRNA was significantly decreased to 57% of control by day 4 and remained significantly decreased for up to a month. TA IIx mRNA was also significantly decreased at 10 and 30 days after denervation. Similar to the soleus, TA Ha mRNA was significantly increased over control 7-14 days after denervation. There were no significant changes in TA MHC protein profile during one month of denervation. In both the soleus and TA, denervation significantly shifted the MHC mRNA profile as early as 4 days following denervation without any corresponding changes at the protein level. Significant mRNA changes without large changes in MHC protein composition continued throughout the denervation period suggesting that the muscle may be prevented from premature functional transitions by mechanisms such as decreased mRNA stability, translational block, or increased turnover of newly synthesized proteins.
European Journal of Biochemistry 09/1998; 256(1):45-50. · 3.58 Impact Factor
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ABSTRACT: Myosin heavy chain (MHC) expression was studied in rat soleus and tibialis anterior (TA) at the mRNA and protein levels following reinnervation 8 and 32 wk after sciatic nerve injury. A sciatic nerve crush or transection injury was produced in the midthigh region of adult female Sprague-Dawley rats. A ribonuclease protection assay was developed to measure four of the adult MHCs (I, IIa, IIx, IIb) in a single sample. MHC mRNA and protein were measured and compared in the same muscles. Eight and thirty-two weeks after a crush injury, the MHC mRNA profiles were similar to control with the exception of soleus MHC IIa and TA MHC IIb, which were significantly less than control at both time points. In contrast, reinnervation of the soleus following a sciatic nerve transection injury resulted in an MHC isoform shift characterized by increases in the relative amounts of fast myosin (IIa and IIx) and a decrease in slow myosin. As expected, significant changes first occurred at the mRNA level followed by changes in protein expression. Thirty-two weeks after transection injury and repair, the primary MHC mRNA isoform in the soleus was MHC IIx. Moreover, at 32 wk, MHC IIb mRNA was detected in 50% of the reinnervated soleus following a transection injury. Reinnervation of the TA following sciatic nerve transection led to replacement of the MHC IIb isoform with MHC IIx.
The American journal of physiology 01/1997; 271(6 Pt 1):C2016-26.
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ABSTRACT: Data supporting the hypothesis that dopamine-2 receptors (D2-R) contribute to time-dependent changes in the hypoxic ventilatory response (HVR) during acclimatization to hypoxia are briefly reviewed. Previous experiments with transgenic animals (D2-R ‘knockout’ mice) support this hypothesis (J. Appl. Physiol. 89 (2000) 1142). However, those experiments could not determine (1) if D2-R in the carotid body, the CNS, or both were involved, or (2) if D2-R were necessary during the acclimatization to hypoxia versus some time prior to chronic hypoxia, e.g. during a critical period of development. Additional experiments on C57BL/6J mice support the idea that D2-R are critical during the period of exposure to hypoxia for normal ventilatory acclimatization. D2-R in carotid body chemoreceptors predominate under control conditions to inhibit normoxic ventilation, but excitatory effects of D2-R, presumably in the CNS, predominate after acclimatization to hypoxia. The inhibitory effects of D2-R in the carotid body are reset to operate primarily under hypoxic conditions in acclimatized rats, thereby optimizing O2-sensitivity.
Respiratory Physiology & Neurobiology.
