Biology subjects

Schleh, M.

Publications and source records attributed to Schleh, M..

3 recordsLinked to original sources

bioRxiv2025

Calorie restriction suppresses aging alpha cell pro-inflammatory signaling

Aging increases risk for type 2 diabetes (T2D), partly through loss of beta cell identity and function driven by metabolic stress and islet inflammation. While calorie restriction (CR) promotes beta cell longevity in young animals, its impact on cellular aging and inflammatory burden in older individuals is unclear. Using SCENIC regulon and multiomic analyses, we find that aging human alpha cells adopt a coordinated inflammatory phenotype marked by IFN-{gamma} signaling to increase major histocompatibility complex (MHC) class I presentation, and CD8+ T cell recruitment and activation towards islets. In T2D, CD8+ T cells further progress towards an effector memory state. CR reduces alpha cell MHC-I expression while subsequently suppressing CD8+ effector status and accompanied by reduced islet inflammation and immune cell infiltration in mice. Together, these findings highlight an alpha cell-immune signaling axis in aging and T2D that may underlie fibrosis and disease pathophysiology.

physiology↗

bioRxiv2024

Deficiency of the hemoglobin-haptoglobin receptor, CD163, worsens insulin sensitivity in obese male mice

Excessive iron accumulation in metabolic organs such as the adipose tissue, liver, and skeletal muscle is associated with increased diabetes risk. Tissue-resident macrophages serve multiple roles including managing inflammatory tone and regulating parachymal iron homeostasis; thus protecting against metabolic dysfunction upon iron overload. The scavenger receptor CD163 is uniquely present on tissue-resident macrophages, and plays a significant role in iron homeostasis by clearing extracellular hemoglobin-haptoglobin complexes, thereby limiting oxidative damage caused by free hemoglobin in metabolic tissues. We show that the absence of CD163 exacerbates glucose intolerance and insulin resistance in male mice with obesity. Additionally, loss of CD163 reduced the expression of iron regulatory genes (Tfr1, Cisd1, Slc40a1) in adipose tissue macrophages and anti-inflammatory (M2-like) bone marrow-derived macrophages (BMDMs). Further, CD163 deficiency mediated a pro-inflammatory shift and limited hemoglobin scavenging specifically in M2-like BMDMs. To this end, iron buffering was diminished in inguinal white adipose tissue (iWAT) macrophages in vivo, which culminated in iron spillover into adipocytes and CD45+CD11B- non-myeloid immune cells in iWAT. These findings show that CD163 on tissue-resident macrophages is critical for their anti-inflammatory and hemoglobin scavenging roles, and its absence results in impaired systemic insulin action in an obese setting. Article HighlightsO_LILoss of CD163 mediates a phenotypic switch in M2-like macrophages towards a pro-inflammatory state. C_LIO_LICD163 is involved in free hemoglobin uptake and catabolism as well as oxidative metabolism, specifically in M2-like macrophages. C_LIO_LIIn inguinal white adipose tissue (iWAT) of CD163 defficient mice, macrophage iron is reduced; while concomitantly, adipocyte and other immune cell iron content is increased. C_LIO_LILoss of CD163 provokes glucose intolerance and insulin resistance in obese male mice. C_LI

physiology↗

bioRxiv2024

Insulin-mediated suppression of fatty acid release predicts whole-body insulin resistance of glucose uptake and skeletal muscle insulin receptor activation

To examine factors underlying why most, but not all adults with obesity exhibit impaired insulin-mediated glucose uptake, we compared: 1) rates of fatty acid (FA) release from adipose tissue, 2) skeletal muscle lipid droplet (LD) characteristics, and 3) insulin signaling events in skeletal muscle collected from cohorts of adults with obesity with "HIGH" versus "LOW" insulin sensitivity for glucose uptake. Seventeen adults with obesity (BMI: 36{+/-}3kg/m2) completed a 2h hyperinsulinemic-euglycemic clamp with stable isotope tracer infusions to measure glucose rate of disappearance (glucose Rd) and FA rate of appearance (FA Ra). Skeletal muscle biopsies were collected at baseline and 30min into the insulin infusion. Participants were stratified into HIGH (n=7) and LOW (n=10) insulin sensitivity cohorts by their glucose Rd during the hyperinsulinemic clamp (LOW<400; HIGH>550 nmol/kgFFM/min/[{micro}U/mL]). Insulin-mediated suppression of FA Ra was lower in LOW compared with HIGH (p<0.01). In skeletal muscle, total intramyocellular lipid content did not differ between cohorts. However, the size of LDs in the subsarcolemmal region (SS) of type II muscle fibers was larger in LOW compared with HIGH (p=0.01). Additionally, insulin receptor (IR) interactions with regulatory proteins CD36 and Fyn were lower in LOW versus HIGH (p<0.01), which aligned with attenuated insulin-mediated Tyr phosphorylation of IR{beta} and downstream insulin-signaling proteins in LOW. Collectively, reduced ability for insulin to suppress FA mobilization, with accompanying modifications in intramyocellular LD size and distribution, and diminished IR interaction with key regulatory proteins may be key contributors to impaired insulin-mediated glucose uptake commonly found in adults with obesity. KEY POINTSO_LIAlthough most adults with obesity exhibit impaired insulin-mediated glucose uptake (insulin resistance), some remain sensitive to insulin. Factors that "protect" adults with obesity from developing resistance to insulin-mediated glucose uptake are poorly understood. C_LIO_LIPotent suppression of fatty acid (FA) mobilization from adipose tissue by insulin is a strong predictor of whole-body insulin-mediated glucose uptake. C_LIO_LIParticipants with higher sensitivity for insulin-mediated glucose uptake had smaller intramyocellular lipid droplets (LDs) within the subsarcolemmal region of type II skeletal muscle fibers. C_LIO_LINovel findings revealed that insulin receptor (IR) interaction with the long-chain fatty acid transport protein, CD36, and the Src-family kinase, Fyn, directly associated with higher rates of glucose uptake under basal and hyperinsulinemic conditions. C_LIO_LITogether, the findings suggest impaired suppression of FA release from adipose tissue associates with reduced glucose uptake in skeletal muscle due in part to a defect in IR activation by CD36/Fyn and altered subcellular LD characteristics. C_LI

physiology↗