Pulmonary surfactants and the respiratory-renal connection in steroid-sensitive nephrotic syndrome of childhood

SIRPα modulates the podocyte cytoskeleton through influencing the phosphorylation of FAK at tyrosine residue 597

Signal regulatory protein α (SIRPα) is recognized as a significant transmembrane protein within the glomeruli that is specifically localized in podocytes, where it plays a role in modulating downstream signaling pathways through phosphorylation. Upon tyrosine phosphorylation of the immunoreceptor tyrosine-based inhibitory motif (ITIM) within SIRPα, protein tyrosine phosphatases are recruited to facilitate the dephosphorylation of downstream signals. Nevertheless, the specific downstream signaling pathways affected by this mechanism have yet to be elucidated. In this study, phosphoproteomic analysis is conducted on podocytes with SIRPα deficiency to identify proteins whose phosphorylation is regulated by SIRPα and the associated signaling pathways in human podocytes. The results reveal significant alterations in biological processes related to cytoskeleton arrangement and cytoskeleton protein binding. Specifically, an increase in FAK tyrosine phosphorylation at Y576 is identified as a potentially crucial signal of the influence of SIRPα on the podocyte cytoskeleton. Our study suggests that SIRPα may facilitate podocyte cytoskeleton rearrangement and migration through the Src/FAK/p38 MAPK signaling pathway. For the first time, we discover increased level of SIRPα, which is strongly linked to urinary protein, in the urine of patients with nephrotic syndrome (NS). Additionally, an increase in urinary FAK level is observed in NS patients, which is positively correlated with both urinary protein level and urinary SIRPα level. These findings suggest that SIRPα and FAK may serve as promising biomarkers for podocytopathies.

Dexamethasone-Associated Hyperglycemia is Not Associated With Infectious Complications After Total Joint Arthroplasty in Diabetic Patients

BACKGROUND

Postoperative infection is a devastating complication of total joint arthroplasty (TJA). Perioperative use of dexamethasone in patients who have diabetes mellitus (DM) remains controversial due to concern for increased infection risk. This study aimed to evaluate the association between dexamethasone and infection risk among patients who have DM undergoing TJA.

METHODS

This was a retrospective cohort study conducted on adult patients who underwent primary, elective total knee arthroplasty (TKA) or total hip arthroplasty (THA) between January 2016 and December 2021 using a large national database. We identified 110,568 TJA patients (TKA: 66.6%; THA: 33.4%), 31.0% (34,298) of which had DM. Patients who received perioperative dexamethasone were compared to those who did not. The primary end points were the 90-day risk of postoperative periprosthetic joint infection, surgical site infection (SSI), and other non-SSI (urinary tract infection, pneumonia, sepsis).

RESULTS

When modeling the association between dexamethasone exposure and study outcomes while accounting for the interaction between dexamethasone and morning blood glucose levels, dexamethasone administration conferred no increased odds of postoperative periprosthetic joint infection nor SSI in diabetics. However, dexamethasone significantly lowered the adjusted odds of other postoperative infections in diabetic patients (TKA: adjusted odds ratio = 09, 95% confidence interval = 0.8 to 1.0, P = .030; THA: adjusted odds ratio = 0.7, 95% confidence interval = 0.6 to 0.9, P = .001); specifically in patients with morning blood glucose levels between 110 to 248 mg/dL in TKA and ≤ 172 mg/dL in THA.

CONCLUSIONS

This study provides strong evidence against withholding dexamethasone in diabetic patients undergoing TJA based on concern for infection. Instead, short-course perioperative dexamethasone reduced infection risk in select patients. The narrative surrounding dexamethasone should shift away from questions about whether dexamethasone is appropriate for diabetic patients, and instead focus on how best to optimize its use.

Leishmania Infection-Induced Proteolytic Processing of SIRPα in Macrophages

The shedding of cell surface receptors may bring synergistic outcomes through the loss of receptor-mediated cell signaling and competitive binding of the shed soluble receptor to its ligand. Thus, soluble receptors have both biological importance and diagnostic importance as biomarkers in immunological disorders. Signal regulatory protein α (SIRPα), one of the receptors responsible for the 'don't-eat-me' signal, is expressed by myeloid cells where its expression and function are in part regulated by proteolytic cleavage. However, reports on soluble SIRPα as a biomarker are limited. We previously reported that mice with experimental visceral leishmaniasis (VL) manifest anemia and enhanced hemophagocytosis in the spleen accompanied with decreased SIRPα expression. Here, we report increased serum levels of soluble SIRPα in mice infected with Leishmania donovani, a causative agent of VL. Increased soluble SIRPα was also detected in a culture supernatant of macrophages infected with L. donovani in vitro, suggesting the parasite infection promotes ectodomain shedding of SIRPα on macrophages. The release of soluble SIRPα was partially inhibited by an ADAM proteinase inhibitor in both LPS stimulation and L. donovani infection, suggesting a shared mechanism for cleavage of SIRPα in both cases. In addition to the ectodomain shedding of SIRPα, both LPS stimulation and L. donovani infection induced the loss of the cytoplasmic region of SIRPα. Although the effects of these proteolytic processes or changes in SIRPα still remain unclear, these proteolytic regulations on SIRPα during L. donovani infection may explain hemophagocytosis and anemia induced by infection, and serum soluble SIRPα may serve as a biomarker for hemophagocytosis and anemia in VL and the other inflammatory disorders.