The pancreatic beta cell is a key site for mediating the effects of leptin on glucose homeostasis

The hormone leptin plays a crucial role in maintenance of body weight and glucose homeostasis. This occurs through central and peripheral pathways, including regulation of insulin secretion by pancreatic beta cells. To study this further in mice, we disrupted the signaling domain of the leptin receptor gene in beta cells and hypothalamus. These mice develop obesity, fasting hyperinsulinemia, impaired glucose-stimulated insulin release, and glucose intolerance, similar to leptin receptor null mice. However, whereas complete loss of leptin function causes increased food intake, this tissue-specific attenuation of leptin signaling does not alter food intake or satiety responses to leptin. Moreover, unlike other obese models, these mice have reduced fasting blood glucose. These results indicate that leptin regulation of glucose homeostasis extends beyond insulin sensitivity to influence beta cell function, independent of pathways controlling food intake. These data suggest that defects in this adipoinsular axis could contribute to diabetes associated with obesity.     

Ligands for kappa-opioid and ORL1 receptors identified from a conformationally constrained peptide combinatorial library.

We have screened a synthetic peptide combinatorial library composed of 2 x 10(7) beta-turn-constrained peptides in binding assays on four structurally related receptors, the human opioid receptors mu, delta, and kappa and the opioid receptor-like ORL1. Sixty-six individual peptides were synthesized from the primary screening and tested in the four receptor binding assays. Three peptides composed essentially of unnatural amino acids were found to show high affinity for human kappa-opioid receptor. Investigation of their activity in agonist-promoted stimulation of [(35)S]guanosine 5'-3-O-(thio)triphosphate binding assay revealed that we have identified the first inverse agonist as well as peptidic antagonists for kappa-receptors. To fine-tune the potency and selectivity of these kappa-peptides we replaced their turn-forming template by other turn mimetic molecules. This "turn-scan" process allowed the discovery of compounds with modified selectivity and activity profiles. One peptide displayed comparable affinity and partial agonist activity toward all four receptors. Interestingly, another peptide showed selectivity for the ORL1 receptor and displayed antagonist activity at ORL1 and agonist activity at opioid receptors. In conclusion, we have identified peptides that represent an entirely new class of ligands for opioid and ORL1 receptors and exhibit novel pharmacological activity. This study demonstrates that conformationally constrained peptide combinatorial libraries are a rich source of ligands that are more suitable for the design of nonpeptidal drugs.     

Leptin increases hepatic insulin sensitivity and protein tyrosine phosphatase 1B expression

Leptin has been shown to improve insulin sensitivity and glucose metabolism in obese diabetic ob/ob mice, yet the mechanisms remain poorly defined. We found that 2 d of leptin treatment improved fasting but not postprandial glucose homeostasis, suggesting enhanced hepatic insulin sensitivity. Consistent with this hypothesis, leptin improved in vivo insulin receptor (IR) activation in liver, but not in skeletal muscle or fat. To explore the cellular mechanism by which leptin up-regulates hepatic IR activation, we examined the expression of the protein tyrosine phosphatase PTP1B, recently implicated as an important negative regulator of insulin signaling. Unexpectedly, liver PTP1B protein abundance was increased by leptin to levels similar to lean controls, whereas levels in muscle and fat remained unchanged. The ability of leptin to augment liver IR activation and PTP1B expression was also observed in vitro in human hepatoma cells (HepG2). However, overexpression of PTP1B in HepG2 cells led to diminished insulin-induced IR phosphorylation, supporting the role of PTP1B as a negative regulator of IR activation in hepatocytes. Collectively, our results suggest that leptin acutely improves hepatic insulin sensitivity in vivo with concomitant increases in PTP1B expression possibly serving to counterregulate insulin action and to maintain insulin signaling in proper balance.     

Periodic lamellipodial contractions correlate with rearward actin waves

Cellular lamellipodia bind to the matrix and probe its rigidity through forces generated by rearward F-actin transport. Cells respond to matrix rigidity by moving toward more rigid matrices using an unknown mechanism. In spreading and migrating cells we find local periodic contractions of lamellipodia that depend on matrix rigidity, fibronectin binding and myosin light chain kinase (MLCK). These contractions leave periodic rows of matrix bound beta3-integrin and paxillin while generating waves of rearward moving actin bound alpha-actinin and MLCK. The period between contractions corresponds to the time for F-actin to move across the lamellipodia. Shortening lamellipodial width by activating cofilin decreased this period proportionally. Increasing lamellipodial width by Rac signaling activation increased this period. We propose that an actin bound, contraction-activated signaling complex is transported locally from the tip to the base of the lamellipodium, activating the next contraction/extension cycle.     

The effects of an acute temperature change on the metabolic recovery from exhaustive exercise in luvenile Atlantic salmon (Salmo salar)

This research examined the influence of acute changes of water temperature on the recovery processes following exhaustive exercise in juvenile Atlantic salmon (Salmo salar). White muscle phosphocreatine (PCr), ATP, lactate, glycogen, glucose, pyruvate, plasma lactate, and plasma osmolality were measured during rest and at 0, 1, 2, and 4 h following exhaustive exercise in fish acclimated and exercised at 12 degrees C and acutely exposed to either 6 degrees C or 18 degrees C water during recovery. An acute exposure to 6 degrees C water during the recovery period resulted in a severe reduction of metabolic recovery in salmon. However, metabolites such as muscle PCr and ATP and plasma lactate recovered very quickly (2-4 h) in fish acutely exposed to 18 degrees C during recovery. Overall, differences exist when postexercise metabolite levels are compared between acclimated fish and those fish acutely exposed to different water temperatures (either higher or lower). Taken together, the findings of the acute experiments suggest that at some point following exercise fish may seek warmer environments to speed the recovery process. However, the relationship between behavioural thermoregulation and recovery following exhaustive exercise in fish is not well understood.     

Francisella novicida LPS has greater immunobiological activity in mice than F. tularensis LPS,and contributes to F. novicida murine pathogenesis

To further understand the role of LPS in the pathogenesis of Francisella infection, we characterized murine infection with F. novicida, and compared immunobiological activities of F. novicida LPS and the LPS from F. tularensis live vaccine strain (LVS). F. novicida had a lower intradermal LD(50) in BALB/cByJ mice than F. tularensis LVS, and mice given a lethal F. novicida dose intraperitoneally died faster than those given the same lethal F. tularensis LVS dose. However, the pattern of in vivo dissemination was similar, and in vitro growth of both bacteria in bone marrow-derived macrophages was comparable. F. novicida LPS stimulated very modest in vitro proliferation of mouse splenocytes at high doses, but F. tularensis LVS LPS did not. Murine bone marrow macrophages treated in vitro with F. novicida LPS produced IL12 and TNF-alpha, but did not produce detectable interferon-gamma, IL10, or nitric oxide; in contrast, murine macrophages treated with F. tularensis LVS LPS produced none of these mediators. In contrast to clear differences in stimulation of proliferation and especially cytokines, both types of purified LPS stimulated early protection against lethal challenge of mice with F. tularensis LVS, but not against lethal challenge with F. novicida. Thus, although LPS recognition may not be a major factor in engendering protection, the ability of F. novicida LPS to stimulate the production of proinflammatory cytokines including TNF-alpha likely contributes to the increased virulence for mice of F. novicida compared to F. tularensis LVS.     

The mammalian passenger protein TD-60 is an RCC1 family member with an essential role in prometaphase to metaphase progression

Passenger proteins migrate from inner centromeres to the spindle midzone during late mitosis, and those described to date are essential both for proper chromosome segregation and for completion of cell cleavage. We have purified and cloned the human passenger protein TD-60, and we here report that it is a member of the RCC1 family and that it binds preferentially the nucleotide-free form of the small G protein Rac1. Using siRNA, we further demonstrate that the absence of TD-60 substantially suppresses overall spindle assembly, blocks cells in prometaphase, and activates the spindle assembly checkpoint. These defects suggest TD-60 may have a role in global spindle assembly or may be specifically required to integrate kinetochores into the mitotic spindle. The latter is consistent with a TD-60 requirement for recruitment of the passenger proteins survivin and Aurora B, and suggests that like other passenger proteins, TD-60 is involved in regulation of cell cleavage.     

Metastasis of bronchogenic carcinoma to the thumb

Bone metastasis in the hand is rare. The etiology is quite different from that of metastasis to other bones; bronchogenic carcinoma is by far the most frequent case. Distal phalanges are mainly involved with irregular osteolysis and cortical destruction. Differential diagnosis of phalangeal metastasis includes osteomyelitis, rheumatoid arthritis and gout. The prognosis is always that of metastatic bronchial cancer with an average survival of three months. Treatment may involve distal digital amputation or antalgic radiotherapy. A case of bronchogenic carcinoma with metastasis to the thumb is presented. The metastasis was located in the distal phalanx of the left thumb. The primary tumor was located in the lung. Treatment consisted of amputation. The overall survival was five months.     

Disruption of the kappa-opioid receptor gene in mice enhances sensitivity to chemical visceral pain, impairs pharmacological actions of the selective kappa-agonist U-50,488H and attenuates morphine withdrawal.

***micro***-, delta- and kappa-opioid receptors are widely expressed in the central nervous system where they mediate the strong analgesic and mood-altering actions of opioids, and modulate numerous endogenous functions. To investigate the contribution of the kappa-opioid receptor (KOR) to opioid function in vivo, we have generated KOR-deficient mice by gene targeting. We show that absence of KOR does not modify expression of the other components of the opioid system, and behavioural tests indicate that spontaneous activity is not altered in mutant mice. The analysis of responses to various nociceptive stimuli suggests that the KOR gene product is implicated in the perception of visceral chemical pain. We further demonstrate that KOR is critical to mediate the hypolocomotor, analgesic and aversive actions of the prototypic kappa-agonist U-50, 488H. Finally, our results indicate that this receptor does not contribute to morphine analgesia and reward, but participates in the expression of morphine abstinence. Together, our data demonstrate that the KOR-encoded receptor plays a modulatory role in specific aspects of opioid function.