Sameer Gupta

Physiological crosstalk between melatonin and glucocorticoid receptor modulates T-cell mediated immune responses in a wild tropical rodent, Funambulus pennanti

Immunoenhancing attributes of melatonin (Mel) on the immunocompromised state induced by glucocorticoid is well known, but the involvement of their receptors in the modulation of immunity has never been studied in any rodent. The present study explores the role of Mel and its receptors (MT1 and MT2) in amelioration of immunocompromised state induced by a synthetic glucocorticoid, dexamethasone (Dex) in a tropical rodent Funambulus pennanti. Immune parameters viz. DTH response, Lymphocyte proliferation, cytokine (IL-2) and antibody production were assessed following pretreatment of Mel and Dex alone or in combination. Mel enhanced the IL-2 production, thymic and splenic lymphocyte proliferation thereby increasing T helper cell associated immune responses and anti-KLH-IgG production. MT1 and MT2 receptor expression was downregulated following Dex treatment while glucocorticoid receptors (GR) expression was downregulated in Mel treated groups suggesting that the immunomodulatory effects of glucocorticoids and Mel are mediated via their receptors. To gain further insights on the role of Mel receptors, we used nonselective melatonin receptor antagonist luzindole which resulted in reversal of most of the immunomodulatory actions of Mel. Therefore, it may be suggested that a physiological cross talk exist between Mel and GR which is of high adaptive significance in wild animals for balancing the immunity during ecologically stressful conditions.

Melatonin membrane receptor type MT1 modulates cell-mediated immunity in the seasonally breeding tropical rodent Funambulus pennanti.

Objective: Despite the evidence for melatonin membrane receptors (MT1R and MT2R) on lymphoid tissues in a wide range of seasonal breeders, their specific potency has never been compared and correlated with cell-mediated immunity. Methods: We used luzindole, a nonselective MT2R antagonist, and 4-phenyl-2-propionamidotetralin (4P-PDOT), a selective MT2R antagonist, to assess the potency of the melatonin receptors MT1 and MT2 in melatonin-induced immunity under both in vivo as well as in vitro conditions. Results: Physiological doses (25 µg/100 g body weight in vivo and 100 and 500 pg/ml in vitro) of melatonin upregulated both MT1R and MT2R expression as well as splenocyte proliferation, while higher doses (100 and 500 µg/100 g body weight in vivo and 1 ng/ml in vitro) downregulated splenocyte proliferation and the expression of both receptors. Luzindole antagonized the expression of both MT1R and MT2R in a dose-dependent manner under in vivo as well as in vitro conditions, while 4P-PDOT blocked the expression of MT2R only during both experimental conditions. Splenocyte proliferation and IL-2 secretion (in vitro) followed the MT1R expression pattern, while the MT2R expression pattern showed no definite relation with either splenocyte proliferation or IL-2 secretion under in vivo and in vitro conditions. Conclusion: Immune function in tropical rodents is directly regulated by melatonin via its high-affinity membrane receptor MT1. MT1R plays a directive role in mediating splenocyte proliferation and IL-2 release, while the MT2R subtype appears not to be required for the immunoenhancing role of melatonin.

Age dependent expression of melatonin membrane receptor (MT1, MT2) and its role in regulation of nitrosative stress in tropical rodent Funambulus pennanti

Age-dependent declining level of melatonin induces free radical load and thereby deteriorates immune function. However, reports are lacking about age-dependent melatonin membrane receptor (MT1 & MT2) expression, their role in regulation of reactive nitrogen species (RNS) and eventually how they affect immunity of a tropical rodent F. pennanti. We checked MT1R, MT2R and iNOS expression in lymphoid organs of young middle and old aged squirrels. Nitrite and nitrate ion concentration (NOx) in lymphoid organs, testes and plasma, lymphocyte proliferation and IL-2 level was recorded. Age-dependent decrease in MT1 and MT2 receptor expression, lymphocyte proliferation, IL-2 level and increased RNS in lymphoid organs, testes and plasma was observed with decreased circulatory melatonin. Androgen and AR expression was increased in middle-aged while declined in old-aged squirrels. Present study suggests that age associated immunosenescence is consequence of increased RNS which might have important relationship with melatonin membrane receptors in F. pennanti.

Effects of thyroid hormone on the chemical constituents of different tissues of the chequered water-snake, Natrix piscator

Abstract l -Thyroxine maintains the body and liver weights of thyroidectomized snakes at the levels found in intact animals but has no effect on kidney weight. The decreases in the levels of muscle glycogen, plasma cholesterol (total, esterified and free), liver esterified fatty acids and cholesterol (esterified), and adipose tissue triglycerides (TG), and the increase in the levels of liver FFA and cholesterol (free) following thyroidectomy are brought up to intact levels by l -thyroxine. However, the concentration of plasma protein, FFA, esterified fatty acids and TG in the plasma and liver, which decreases, and of FFA in the adipose tissue and glycogen in liver, which increases, following thyroidectomy, are increased and decreased, respectively, when compared to intact snakes following the administration of l -thyroxine into thyroidectomized snakes. Plasma glucose level, on the other hand was not affected by thyroidectomy but was elevated by l -thyroxine.

Effects of L-thyroxine on the intermediary metabolism of the Spotted Munia, Lonchura punctulata

Abstract L-Thyroxine was injected over a period of 1 mo into Spotted Munia, Lonchura punctulata , and the following variables were measured: glucose and protein in the plasma, glycogen in the muscle and liver, cholesterol and fatty acid esters in the liver, and plasma, and free fatty acids and triglycerides in the liver, plasma, and adipose tissue. The hormone had different effects at different dose levels on the plasma proteins, liver free fatty acids, and plasma and liver fatty acid esters. It caused significant decrease in hepatic glycogen and triglycerides and significant increase in the plasma and adipose tissue free fatty acids. Low and high doses decreased significantly plasma triglycerides and muscle glycogen, respectively, and the mid dose decreased plasma glucose and adipose triglycerides. Hepatic and plasma cholesterol was not affected significantly.

Photoperiodic regulation of nuclear melatonin receptor RORα in lymphoid organs of a tropical rodent Funambulus pennanti: role in seasonal oxidative stress.

The orphan nuclear receptor RORα of RZR/ROR family has been suggested to mediate the genomic actions of melatonin on the expression of antioxidant enzymes. However, no direct evidences exist. In the present study we explored the role of photoperiod (natural and artificial) in regulation of RORα and its association with the photoperiod induced antioxidant defense system in the lymphoid organs (spleen and thymus) of seasonally breeding, tropical squirrels, Funambulus pennanti. The photoperiod mediated regulation of antioxidant status was checked along with the RORα expression and circulatory melatonin level in the squirrels. The enhancement of the antioxidant capacity of serum and lymphoid organ was concomitant with the short photoperiod (10L:14D) induced high levels of plasma melatonin. Further, peripheral melatonin level enhanced the AANAT activity as well as the melatonin synthesis in the lymphoid tissues. RORα expression presented an inverse correlation with the plasma level of melatonin as well as the short day induced antioxidant enzyme activity in the lymphoid organs. The results suggest that for reduction of seasonal oxidative stress melatonin might not be utilizing the nuclear receptor RORα pathway; rather the rise in circulatory melatonin collectively with tissue specific melatonin might be protecting the splenic and thymic lymphocytes from the seasonal oxidative stress.

Short day length enhances physiological resilience of the immune system against 2-deoxy-d-glucose-induced metabolic stress in a tropical seasonal breeder Funambulus pennanti

&NA; Studies demonstrate the importance of metabolic resources in the regulation of reproduction and immune functions in seasonal breeders. In this regard, the restricted energy availability can be considered as an environmental variable that may act as a seasonal stressor and can lead to compromised immune functions. The present study explored the effect of photoperiodic variation in the regulation of immune function under metabolic stress condition. The T‐cell‐dependent immune response in a tropical seasonal breeder Funambulus pennanti was studied following the inhibition of cellular glucose utilization with 2‐deoxy‐D‐glucose (2‐DG). 2‐DG treatment resulted in the suppression of general (e.g., proliferative response of lymphocytes) and antigen‐specific [anti‐keyhole limpet hemocyanin IgG titer and delayed‐type hypersensitivity response] T‐cell responses with an activation of the hypothalamic–pituitary–adrenal axis, which was evident from the increased levels of plasma corticosterone. 2‐DG administration increased the production of inflammatory cytokines [interleukin (IL)‐1&bgr; and tumor necrosis factor (TNF)‐&agr;] and decreased the autocrine T‐cell growth factor IL‐2. The immunocompromising effect of 2‐DG administration was retarded in animals exposed to short photoperiods compared with the control and long photoperiod‐exposed groups. This finding suggested that short photoperiodic conditions enhanced the resilience of the immune system, possibly by diverting metabolic resources from the reproductive organs toward the immune system. In addition, melatonin may have facilitated the energy “trade‐off” between reproductive and immune mechanisms, thereby providing an advantage to the seasonal breeders for their survival during stressful environmental conditions. Highlights2‐DG administration altered testis and lymphoid organ weights in animals exposed to LDL and NDL conditions.2‐DG administration attenuated T‐cell‐dependent immune responses under LDL and NDL conditions.SDL conditions retarded 2‐DG‐induced levels of corticosterone.SDL‐induced increase in melatonin levels may be an adaptive advantage for seasonal breeders to survive under stressful conditions.

Photoperiodic modulation of local melatonin synthesis and its role in regulation of thymic homeostasis in Funambulus pennanti

The effect of photo-neuroendocrine system on the thymic (immune) functions is mediated by gonadal steroid and the pineal hormone melatonin. The present study explored the effect of photoperiod on the thymic melatonergic system and its role in protection of thymic T-cells from the testosterone induced seasonal oxidative stress and apoptosis. Exposure to long day-length (LD) was noted to decrease local (thymic) melatonin content and induce oxidative stress and apoptosis in the thymus. Increased peripheral level of testosterone upregulated the androgen receptor expression and, consequently reduced proliferation response of the thymocytes. Short day conditions (SD) however, reversed the effect of LD on the thymic physiology. Low level of testosterone was concomitant with diminished nitro-oxidative stress and decreased expression of redox sensitive factors (NF-κB, p53 and Bax/Bcl-2 ratio) in the thymus. SD retarded activation of caspase-3 resulting in procaspase-3 accumulation. Further, in vitro treatment of thymocytes with AR antagonist flutamide impaired the sensitivity of thymocytes to androgen and reversed the deleterious effects of testosterone on the proliferative and apoptotic responses of thymocytes. Therefore, it can be suggested that thymus derived melatonin protects thymic T-cells from testosterone induced seasonal oxidative stress, apoptosis and also acts as a potent paracrine factor for maintenance of redox status to ensure thymocyte survival.

Annual variation and role of male hormone in the renal β-glucuronidase activity of the chequered water snake, Natrix piscator

In a local water snake, Natrix piscator, the effects of castration and testosterone on kidney weight, renal β-glucuronidase (lysosomal enzyme) and height of the cells lining the sexual segment were studied. Renal β-glucuronidase activity was high in the progressive and peak phases of the testis while the weight of the kidney was high during the regressive phase. Castration decreased renal β-glucuronidase activity, height of the cells lining the sexual segment and weight of the kidney. Testosterone increased the activity of the enzyme and height of the cells lining the sexual segment of castrated snakes. Kidney weight in castrated snakes was not affected by testosterone administration.