Thyroid hormones control lipid composition and membrane fluidity of skeletal muscle sarcolemma

Are serum thyroid hormone, parathormone, calcium, and vitamin D levels associated with lumbar spine degeneration? A cross-sectional observational clinical study

PURPOSE

Low back pain (LBP) impairs the quality of life and rises healthcare costs. The association of spine degeneration and LBP with metabolic disorders have been reported, previously. However, metabolic processes related with spine degeneration remained unclear. We aimed to analyze whether serum thyroid hormones, parathormone, calcium, and vitamin D levels were associated with lumbar intervertebral disc degeneration (IVDD), Modic changes, and fatty infiltration in the paraspinal muscles.

METHODS

We cross-sectionally analyzed a retrospective database. Patients who visited internal medicine outpatient clinics with suspect of endocrine disorders and chronic LBP were searched. Patients with biochemistry results within 1 week before lumbar spine magnetic resonance imaging (MRI) were included. Age- and gender-matched cohorts were made-up and analyzed.

RESULTS

Patients with higher serum free thyroxine levels were more likely to have severe IVDD. They were also more likely to have fattier multifidus and erector spinae at upper lumbar levels, less fatty psoas and less Modic changes at lower lumbar levels. Higher PTH levels were observed in patients with severe IVDD at L4-L5 level. Patients with lower serum vitamin D and calcium levels had more Modic changes and fattier paraspinal muscles at upper lumbar levels.

CONCLUSION

Serum hormone, vitamin D, and calcium levels were associated with not only IVDD and Modic changes but also with fatty infiltration in the paraspinal muscles, mainly at upper lumbar levels in patients with symptomatic backache presenting to a tertiary care center. Complex inflammatory, metabolic, and mechanical factors present in the backstage of spine degeneration.

Effect of thyroid hormone on the distribution and activity of Na, K-ATPase in ventricular myocardium

Employing detergent-free sucrose-density gradient fractionation method we isolated cholesterol-rich lighter membrane fractions containing approximately 10% of protein, approximately 30% of cholesterol in membranes of ventricular myocardium. Cholesterol-rich lighter membrane fractions contain >70% of Na, K-ATPase and caveolins 1 and 3 and <10% of beta-actin. Treatment of hypothyroid rats with T(3) increased the relative abundance of both alpha1 and beta1 Na, K-ATPase subunits in total membranes by 4- to 5-fold (with no change in caveolin-3), and resulted in 1.9-fold increase in enzyme activity. T(3)-induced Na, K-ATPase subunits were preferentially distributed to the lighter fractions (#s 4, 5 and 6); and increased abundance of alpha1 and beta1 were 34-70% and 43-68%, respectively. We conclude that the activity of Na, K-ATPase is not uniform in cardiac membranes, and while a significant amount of Na, K-ATPase is present in cardiac cholesterol-rich membrane fractions, the intrinsic activity is significantly less than the enzyme present in relatively cholesterol-poor membranes.

Body size related adaptations of the avian myocardial phospholipid fatty acyl chain composition

The myocardial phospholipid fatty acid (FA) composition (mol %) of 7 avian species was determined, in a body mass range from 150 g (Japanese quail, Coturnix coturnix japonica) to 19 kg (turkey, Meleagris gallopavo). Significant allometric increases were found for C16:1 n7 (allometric exponent: B=0.15), C18:1 n7 (B=0.08), C18:1 n9 (B=0.24), C20:1 n9 (B=0.22) and C20:3 n3 (B=0.12); moreover, total monounsaturates (B=0.20) and the sum of n9 FAs (B=0.24) was also positively related to body mass. The total n3 FAs (B=-0.36), and within them C22:5 n3 (B=-0.41) and C22:6 n3 (B=-0.60) showed allometric declines, such as total polyunsaturated fatty acids (PUFA; B=-0.01), unsaturation index (B=-0.03) and mean FA chain length (B=-0.003). Comparing our results with earlier published data on avian skeletal muscle and divergent mammalian tissues, the allometric scaling of the above membrane forming fatty acids seems to be part of a general relationship postulated as the theory "membranes as metabolic pacemakers". In addition, the cardiac muscle malondialdehyde concentration was negatively related to body mass (B=-0.16), referring to a lower level of lipid peroxidation in larger birds, and vice versa, indicating a progressive myocardial lipid peroxidation in smaller-bodied species.

Evaluation of indices of skeletal muscle contraction in areas of referred hyperalgesia from an artificial ureteric stone in rats

This study examined indices of skeletal muscle contraction in a rat model of referred muscle hyperalgesia from artificial ureteric calculosis [left oblique muscle (OE) for ipsilateral stone]. In specimens from the left versus right OE of stone-implanted female rats, a significant increase was found in membrane fluidity (P<0.01) and Ca(2+)-ATPase activity (P<0.0001) and a significant decrease in 3H-ryanodine binding (P<0.0001) and in I band length/sarcomere length ratio (contraction index) (P<0.01). The increase in Ca(2+)-ATPase activity was directly and significantly related to the number of rats' ureteral 'crises' (P<0.02). The results indicate a state of contraction in the hyperalgesic muscle, whose extent correlates to the algogenic activity of the ureteral stone.

Sulfate and chloride transport in Caco-2 cells: differential regulation by thyroxine and the possible role of DRA gene

The current studies were undertaken to establish an in vitro cellular model to study the transport of SO and Cl(-) and hormonal regulation and to define the possible function of the downregulated in adenoma (DRA) gene. Utilizing a postconfluent Caco-2 cell line, we studied the OH(-) gradient-driven (35)SO and (36)Cl(-) uptake. Our findings consistent with the presence of an apical carrier-mediated (35)SO/OH(-) exchange process in Caco-2 cells include: 1) demonstration of saturation kinetics [Michaelis-Menten constant (K(m)) of 0.2 +/- 0.08 mM for SO and maximum velocity of 1.1 +/- 0.2 pmol x mg protein(-1) x 2 min(-1)]; 2) sensitivity to inhibition by DIDS (K(i) = 0.9 +/- 0.3 microM); and 3) competitive inhibition by oxalate and Cl(-) but not by nitrate and short chain fatty acids, with a higher K(i) (5.95 +/- 1 mM) for Cl(-) compared with oxalate (K(i) = 0.2 +/- 0.03 mM). Our results also suggested that the SO/OH(-) and Cl(-)/OH(-) exchange processes in Caco-2 cells are distinct based on the following: 1) the SO/OH(-) exchange was highly sensitive to inhibition by DIDS compared with Cl(-)/OH(-) exchange activity (K(i) for DIDS of 0.3 +/- 0.1 mM); 2) Cl(-) competitively inhibited the SO/OH(-) exchange activity with a high K(i) compared with the K(m) for SO, indicating a lower affinity for Cl(-); 3) DIDS competitively inhibited the Cl(-)/OH(-) exchange process, whereas it inhibited the SO/OH(-) exchange activity in a mixed-type manner; and 4) utilizing the RNase protection assay, our results showed that 24-h incubation with 100 nM of thyroxine significantly decreased the relative abundance of DRA mRNA along with the SO/OH(-) exchange activity but without any change in Cl(-)/OH(-) exchange process. In summary, these studies demonstrated the feasibility of utilizing Caco-2 cell line as a model to study the apical SO/OH(-) and Cl(-)/OH(-) exchange processes in the human intestine and indicated that the two transporters are distinct and that DRA may be predominantly a SO transporter with a capacity to transport Cl(-) as well.

Mechanisms involved in the cellular calcium homeostasis in vascular smooth muscle: calcium pumps

The regulation of cytosolic Ca2+ homeostasis is essential for cells, and particularly for vascular smooth muscle cells. In this regulation, there is a participation of different factors and mechanisms situated at different levels in the cell, among them Ca2+ pumps play an important role. Thus, Ca2+ pump, to extrude Ca2+; Na+/Ca2+ exchanger; and different Ca2+ channels for Ca2+ entry are placed in the plasma membrane. In addition, the inner and outer surfaces of the plasmalemma possess the ability to bind Ca2+ that can be released by different agonists. The sarcoplasmic reticulum has an active role in this Ca2+ regulation; its membrane has a Ca2+ pump that facilitates luminal Ca2+ accumulation, thus reducing the cytosolic free Ca2+ concentration. This pump can be inhibited by different agents. Physiologically, its activity is regulated by the protein phospholamban; thus, when it is in its unphosphorylated state such a Ca2+ pump is inhibited. The sarcoplasmic reticulum membrane also possesses receptors for 1,4,5-inositol trisphosphate and ryanodine, which upon activation facilitates Ca2+ release from this store. The sarcoplasmic reticulum and the plasmalemma form the superficial buffer barrier that is considered as an effective barrier for Ca2+ influx. The cytosol possesses different proteins and several inorganic compounds with a Ca2+ buffering capacity. The hypothesis of capacitative Ca2+ entry into smooth muscle across the plasma membrane after intracellular store depletion and its mechanisms of inhibition and activation is also commented.

Effects of induced hypo- and hyperthyroidism on immune function and plasma biochemistry in mallards (Anas platyrhynchos)

Hypo- or hyperthyroid states were induced in adult male mallards (Anas platyrhynchos) by subchronic exposure to daily injections of methimazole or a 9:1 ratio of thyroxine (T4): triiodothyronine (T3). The levels of T4 given were 0, 125, 250, or 500 micrograms/kg/day and for methimazole; 10 mg/kg/day for 22 or 21 days. Plasma T3 showed a lasting decrease with T4:T3 treatment, despite the attempt to maintain the normal T4:T3 ratio. Antibody formation to sheep red blood cells was decreased only at the 125 micrograms/kg/day dose of T4, and was unaffected by methimazole treatment. Natural killer cell activity to RP-9 tumor cells and macrophage phagocytosis of killed, opsonized Saccaromyces cereviseae were unaffected by treatment throughout the study. However, lectin-dependent cellular cytotoxic activity to RP-9 tumor cells was significantly decreased after 21 days of methimazole treatment, indicating that hypothyroidism may have an influence on cell-mediated immunity. Hypo- and hyperthyroid conditions had opposing effects on plasma cholesterol levels.

Electrophysiological properties of the hyperthyroid rat heart

We have studied the effects of in vivo administration of different T3 doses to thyroidectomized rats on electrophysiological properties, measured in vitro, of papillary muscle fibers. The treatment with increasing T3 doses was associated with a significant reduction of the action potential duration up to a dose as large as 25 micrograms/100 g body weight every second day. The treatment with larger doses of T3 tended to restore the values of the action potential duration present in animals treated with physiological doses (5 micrograms/100 g body weight every second day). Action potential duration is frequency dependent. As the stimulation rate was increased from 1 to 5 Hz, this duration increased in all groups. However the difference between the rat groups remained significant. The cardiac frequency measured in unanaesthetized rats increased as the T3 doses. Furthermore the intrinsic frequency showed a similar increase, indicating a direct effect of T3 on the pacemaker cells in all thyroid states. The mechanism of this action of the thyroid hormone is not, however clear.

The Ca(2+)-transport ATPases from the plasma membrane

The initial studies on the plasma membrane (PM) Ca(2+)-transport ATPases were made in the erythrocyte, a structure that can not be taken as representing a typical eukaryotic cell. In other cell types however, the study of the PM Ca(2+)-transport ATPase is complicated by the simultaneous expression of related Ca(2+)-pumps in intracellular stores. Whereas there are as yet no known specific inhibitors for the PM Ca(2+)-transport ATPase, a number of selective inhibitors for the endo(sarco)plasmic reticulum Ca2+ pumps have been described: thapsigargin, cyclopiazonic acid and 2,5-di-(tert-butyl)-1,4-benzohydroquinone. With the recent introduction of the molecular biological approach, it became quickly obvious that a family of at least 5 different PM Ca(2+)-transport ATPase genes govern the tissue-dependent expression of PM Ca2+ pumps. Moreover alternative splicing of the primary gene transcripts was found to further enhance the number of pump variants. The PM Ca(2+)-transport ATPase are subject to modulatory control by calmodulin, by acidic phospholipids, and by the known families of protein kinases. Each of the ensuing effects are mutually related and interdependent. The wide variety PM Ca2+ pump isoforms and their regulation by such an intricate modulatory network allows the distinct tissues to adapt most adequately to the prevailing tissue and stimulus specific requirements.