Heat shock transcription factors demonstrate a distinct mode of interaction with mitotic chromosomes.

A large number of transcription factors have been shown to bind and interact with mitotic chromosomes, which may promote the efficient reactivation of transcriptional programs following cell division. Although the DNA-binding domain (DBD) contributes strongly to TF behavior, the mitotic behaviors of TFs from the same DBD family may vary. To define the mechanisms governing TF behavior during mitosis in mouse embryonic stem cells, we examined two related TFs: Heat Shock Factor 1 and 2 (HSF1 and HSF2). We found that HSF2 maintains site-specific binding genome-wide during mitosis, whereas HSF1 binding is somewhat decreased. Surprisingly, live-cell imaging shows that both factors appear excluded from mitotic chromosomes to the same degree, and are similarly more dynamic in mitosis than in interphase. Exclusion from mitotic DNA is not due to extrinsic factors like nuclear import and export mechanisms. Rather, we found that the HSF DBDs can coat mitotic chromosomes, and that HSF2 DBD is able to establish site-specific binding. These data further confirm that site-specific binding and chromosome coating are independent properties, and that for some TFs, mitotic behavior is largely determined by the non-DBD regions.

Focal cooling of brain parenchyma in a transient large vessel occlusion model: proof-of-concept.

INTRODUCTION: The neuroprotective benefit of therapeutic hypothermia (TH) has been demonstrated, but systemic side effects and time required to achieve effective TH in acute ischemic stroke (AIS) care limits clinical use. We investigate rapid and localized cooling using a novel insulated catheter in an ischemia-reperfusion model. METHODS: In phase I (n=4), cold saline was delivered to the canine internal carotid artery via an insulated catheter. Temperature was measured using intracerebral thermocouples. The coolant flow rate was varied to meet a target temperature of 31-32°C in the hemisphere infused. In phase II (n=8), a temporary middle cerebral artery occlusion was created. Five dogs underwent localized TH at the optimal flow rate from phase I, and the remaining animals were untreated controls. Cooling was initiated 5 min before recanalization and continued for an additional 20 min following 45 min of occlusion duration. The outcome was infarct volume and neurological function. RESULTS: Ipsilateral tissue cooling rates were 2.2±2.5°C/min at a flow rate of 20-40 mL/min with an observed minimum of 23.8°C. Tissue cooling was localized to the ipsilateral side of the infusion with little impact on temperatures of the core or contralateral hemisphere of the brain. In phase II, animals tolerated TH with minimal systemic impact. Infarct volume in treated animals was 0.2±0.2 cm3, which was smaller than in sham animals (3.8±1.0 cm3) as well as six untreated historical control animals (4.0±2.8 cm3) (p=0.013). CONCLUSIONS: Proof-of-concept data show that localised brain TH can be quickly and safely achieved through a novel insulated catheter. The small infarct volumes suggest potential benefit for this approach.

Myocardial tissue salvage is correlated with ischemic border region temperature at reperfusion.

OBJECTIVES: Our pilot study investigated the association between region-specific myocardial tissue temperature and tissue salvage using a novel tri-lumen cooling catheter to provide rapid localized cooling directly to the heart in an open-chest porcine model of ischemia-reperfusion. BACKGROUND: Therapeutic hypothermia remains a promising strategy to limit reperfusion injury following myocardial ischemia. METHODS: Large swine underwent 60 min of coronary occlusion followed by 3 hr of reperfusion. Prior to inducing ischemia, six temperature probes were placed directly on the heart, monitoring myocardial temperatures in different locations. Hemodynamic parameters and core temperature were also collected. Approximately 15 min prior to reperfusion, the cooling catheter was inserted via femoral artery and the distal tip advanced proximal to the occluded coronary vessel under fluoroscopic guidance. Autologous blood was pulled from the animal via femoral sheath and delivered through the central lumen of the cooling catheter, delivering at 50 ml/min, 27°C at the distal tip. Cooling was continued for an additional 25 min after reperfusion followed by a 5-min controlled rewarming. Hearts were excised and assessed for infarct size per area at risk. RESULTS: Although cooling catheter performance was consistent throughout the study (38 W), the resulting tissue cooling was not. Our results show a correlation between myocardial tissue salvage and ischemic border region (IBR) temperature at the time of reperfusion (R2 = 0.59, p = 0.027). IBR tissue is the tissue located at the boundary between healthy and ischemic tissues. CONCLUSIONS: Our findings suggest that localized, rapid, short-term myocardial tissue cooling has the potential to limit reperfusion injury in humans.

Infusion warm during selective hypothermia in acute ischemic stroke.

INTRODUCTION: Mechanical thrombectomy (MT) has dramatically improved the prognosis for acute ischemic stroke (AIS) patients. Despite high recanalization rates, up to half of the patients will not present a good neurological outcome after MT. Therapeutic hypothermia is perhaps the most robust neuroprotectant studied preclinically. MATERIALS AND METHODS: We explored various warming effects that can reduce the effectiveness or potency of selective hypothermia during AIS under conditions similar to actual clinical care. Four different selective hypothermia layouts were chosen. Layouts 1 and 2 used a single catheter without and with an insulated IV bag. Layouts 3 and 4 used two catheters arrange coaxially, without and with an insulated IV bag. Independent variables measured were IV bag exit temperature, catheter inlet temperature, and catheter outlet temperature at four different flow rates ranging from 8 to 25 ml/min over an infusion duration of 20 min. RESULTS: Dominant warming occurs along the catheter pathway compared to warming along the infusion line pathway, ranging from 66% to 72%. Coaxial configurations provided an approximate 4°C cooler temperature benefit on delivered infusate over a single catheter. Brain tissue temperature predictions show that the maximum cooling layout, Layout 4 at maximum flow provides a 1°C within 5 min. CONCLUSION: Significant rewarming effects occur along the infusate flow path from IV bag to site of injury in the brain. Previous selective hypothermia clinical work, using flow rates and equipment at conditions similar to our study, likely produced rapid but not deep tissue cooling in the brain (~ 1°C).

Heat transfer analysis of catheters used for localized tissue cooling to attenuate reperfusion injury.

Recent revascularization success for ischemic stroke patients using stentrievers has created a new opportunity for therapeutic hypothermia. By using short term localized tissue cooling interventional catheters can be used to reduce reperfusion injury and improve neurological outcomes. Using experimental testing and a well-established heat exchanger design approach, the ɛ-NTU method, this paper examines the cooling performance of commercially available catheters as function of four practical parameters: (1) infusion flow rate, (2) catheter location in the body, (3) catheter configuration and design, and (4) cooling approach. While saline batch cooling outperformed closed-loop autologous blood cooling at all equivalent flow rates in terms of lower delivered temperatures and cooling capacity, hemodilution, systemic and local, remains a concern. For clinicians and engineers this paper provides insights for the selection, design, and operation of commercially available catheters used for localized tissue cooling.

Expression and characterization of the intracellular vanilloid receptor (TRPV1) in bronchi from patients with chronic cough.

TRPV1 is a modulator of noxious stimuli known to be important in the cough reflex. We have compared the expression of TRPV1 in normal human airways and those from patients with chronic cough and found that there is up regulation in airways smooth muscle in disease. This increased expression appears to be intracellular and we have therefore examined the role of intracellular rat and human TRPV1 activity was found using intracellular calcium signalling with human intracellular TRPV1 being located in a thapsigargin insensitive compartment. Increase in TRPV1 activity may have a role in the airway hypersensitivity seen in chronic cough.