Collateral development: the quest continues

β-Arrestin2 Is Critically Involved in the Differential Regulation of Phosphosignaling Pathways by Thyrotropin-Releasing Hormone and Taltirelin

In recent years, thyrotropin-releasing hormone (TRH) and its analogs, including taltirelin (TAL), have demonstrated a range of effects on the central nervous system that represent potential therapeutic agents for the treatment of various neurological disorders, including neurodegenerative diseases. However, the molecular mechanisms of their actions remain poorly understood. In this study, we investigated phosphosignaling dynamics in pituitary GH1 cells affected by TRH and TAL and the putative role of β-arrestin2 in mediating these effects. Our results revealed widespread alterations in many phosphosignaling pathways involving signal transduction via small GTPases, MAP kinases, Ser/Thr- and Tyr-protein kinases, Wnt/β-catenin, and members of the Hippo pathway. The differential TRH- or TAL-induced phosphorylation of numerous proteins suggests that these ligands exhibit some degree of biased agonism at the TRH receptor. The different phosphorylation patterns induced by TRH or TAL in β-arrestin2-deficient cells suggest that the β-arrestin2 scaffold is a key factor determining phosphorylation events after TRH receptor activation. Our results suggest that compounds that modulate kinase and phosphatase activity can be considered as additional adjuvants to enhance the potential therapeutic value of TRH or TAL.

Native Coronary Collateral Microcirculation Reserve in Rat Hearts

Background We occasionally noticed that native collateral blood flow showed a recessive trend in the early stages of acute myocardial infarction in rats, which greatly interferes with the accurate assessment of native collateral circulation levels. Here, we sought to recognize the coronary collateral circulation system in depth, especially the microcirculation part, on this basis. Methods and Results In this study, we detected native collateral flow with positron emission tomography perfusion imaging in rats and found that the native flow is relatively abundant when it is initially recruited. However, this flow is extremely unstable in the early stage of acute myocardial infarction and quickly fails. We used tracers to mark the collateral in an ischemic area and a massive preformed collateral network was labeled. The ultrastructures of these collateral microvessels are flawed, which contributes to extensive leakage and consequent interstitial edema in the ischemic region. Conclusions An unrecognized short-lived native coronary collateral microcirculation reserve is widely distributed in rat hearts. Recession of collateral blood flow transported by coronary collateral microcirculation reserve contributes to instability of native collateral blood flow in the early stage of acute myocardial infarction. The immature structure determines that these microvessels are short-lived and provide conditions for the development of early interstitial edema in acute myocardial infarction.

A Grading Scale for Pial Collaterals in Middle Cerebral Artery Total Occlusion Based on Time-of-flight MR Angiography Source Images

PURPOSE

To verify whether a new grading based on time-of-flight magnetic resonance angiography source images (TOF-MRAsi) can reflect the abundance of pial collaterals, in patients with total occlusion of M1 segment of middle cerebral artery in the chronic stage.

METHODS

In this single-center retrospective study, consecutive patients with total occlusion of M1 segment of middle cerebral artery, with both magnetic resonances angiography and digital subtraction angiography image were included. Time-of-flight magnetic resonance angiography source images were evaluated in a blinded fashion for pial collaterals (PCs) that were graded on a four-point scale. Good and poor PCs were defined as TOF-MRAsis grade <2 and ≥2, respectively. Receiver operating characteristic curve analysis was done to calculate the area under curve, sensitivity, and specificity.

RESULTS

A total of 26 patients were included. The inter-reader agreement for time TOF-MRAsi and digital subtraction angiography images were 0.930 and 0.843, respectively. Compared with digital subtraction angiography grading, the area under curve of pial collateral grading based on TOF-MRAsi was 0.830 (0.636-1.000; P = 0.006). The sensitivity and specificity were 0.700 and 0.933, respectively. The modified Rankin Scale at follow-up was lower in patients with good PCs than in those with poor PCs (0[0, 1] vs. 1[1, 3], P = 0.055), although statistical significance was not reached.

CONCLUSION

The grading scale based on TOF-MRAsi could be a new empirical approach for pial collateral evaluation. The clinical use of the proposed approach for identifying patients with total occlusion of middle cerebral artery with a high risk of poor outcome requires evaluation in further studies.