Laminin-α4 Negatively Regulates Adipocyte Beiging Through the Suppression of AMPKα in Male Mice.

Laminin-α4 (LAMA4) is an extracellular matrix protein implicated in the regulation of adipocyte differentiation and function. Prior research describes a role for LAMA4 in modulating adipocyte thermogenesis and uncoupling protein-1 (UCP1) expression in white adipose; however, the mechanisms involved are poorly understood. Here, we describe that Lama4 knockout mice (Lama4-/-) exhibit heightened mitochondrial biogenesis and peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) expression in subcutaneous white adipose tissue (sWAT). Furthermore, the acute silencing of LAMA4 with small interfering RNA in primary murine adipocytes was sufficient to upregulate the expression of thermogenic markers UCP1 and PR domain containing 16 (PRDM16). Silencing also resulted in an upregulation of PGC1-α and adenosine 5'-monophosphate-activated protein kinase (AMPK)-α expression. Subsequently, we show that integrin-linked kinase (ILK) is downregulated in the sWAT of Lama4-/- mice, and its silencing in adipocytes similarly resulted in elevated expression of UCP1 and AMPKα. Last, we demonstrate that treatment of human induced pluripotent stem cell-derived thermogenic adipocytes with LAMA4 (LN411) inhibited the expression of thermogenic markers and AMPKα. Overall, our results indicate that LAMA4 negatively regulates a thermogenic phenotype and pathways involving mitochondrial biogenesis in adipocytes through the suppression of AMPKα.

Laminin-α4 Is Upregulated in Both Human and Murine Models of Obesity.

Obesity affects nearly one billion globally and can lead to life-threatening sequelae. Consequently, there is an urgent need for novel therapeutics. We have previously shown that laminin, alpha 4 (Lama4) knockout in mice leads to resistance to adipose tissue accumulation; however, the relationship between LAMA4 and obesity in humans has not been established. In this study we measured laminin-α chain and collagen mRNA expression in the subcutaneous white adipose tissue (sWAT) of mice placed on chow (RCD) or 45% high fat diet (HFD) for 8 weeks, and also in HFD mice then placed on a "weight loss" regimen (8 weeks HFD followed by 6 weeks RCD). To assess extracellular matrix (ECM) components in humans with obesity, laminin subunit alpha mRNA and protein expression was measured in sWAT biopsies of female control subjects (BMI<30) or subjects with obesity undergoing bariatric surgery at the University of Chicago Medical Center (BMI>35) both before and three months after surgery. Lama4 was significantly higher in sWAT of HFD compared to RCD mice at both the RNA and protein level (p<0.001, p<0.05 respectively). sWAT from human subjects with obesity also showed significantly higher LAMA4 mRNA (p<0.01) and LAMA4 protein expression (p<0.05) than controls. Interestingly, even though LAMA4 expression was increased in both humans and murine models of obesity, no significant difference in Lama4 or LAMA4 expression was detected following short-term weight loss in either mouse or human samples, respectively. From these results we propose a significant association between obesity and elevated LAMA4 expression in humans, as well as in mouse models of obesity. Further studies should clarify the mechanisms underlying this association to target LAMA4 effectively as a potential therapy for obesity.

SMRT Regulates Metabolic Homeostasis and Adipose Tissue Macrophage Phenotypes in Tandem.

The Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) is a nuclear corepressor, regulating the transcriptional activity of many transcription factors critical for metabolic processes. While the importance of the role of SMRT in the adipocyte has been well-established, our comprehensive understanding of its in vivo function in the context of homeostatic maintenance is limited due to contradictory phenotypes yielded by prior generalized knockout mouse models. Multiple such models agree that SMRT deficiency leads to increased adiposity, although the effects of SMRT loss on glucose tolerance and insulin sensitivity have been variable. We therefore generated an adipocyte-specific SMRT knockout (adSMRT-/-) mouse to more clearly define the metabolic contributions of SMRT. In doing so, we found that SMRT deletion in the adipocyte does not cause obesity-even when mice are challenged with a high-fat diet. This suggests that adiposity phenotypes of previously described models were due to effects of SMRT loss beyond the adipocyte. However, an adipocyte-specific SMRT deficiency still led to dramatic effects on systemic glucose tolerance and adipocyte insulin sensitivity, impairing both. This metabolically deleterious outcome was coupled with a surprising immune phenotype, wherein most genes differentially expressed in the adipose tissue of adSMRT-/- mice were upregulated in pro-inflammatory pathways. Flow cytometry and conditioned media experiments demonstrated that secreted factors from knockout adipose tissue strongly informed resident macrophages to develop a pro-inflammatory, MMe (metabolically activated) phenotype. Together, these studies suggest a novel role for SMRT as an integrator of metabolic and inflammatory signals to maintain physiological homeostasis.

APP-Mediated Signaling Prevents Memory Decline in Alzheimer's Disease Mouse Model.

Amyloid precursor protein (APP) and its metabolites play key roles in Alzheimer's disease (AD) pathophysiology. Whereas short amyloid-ß (Aß) peptides derived from APP are pathogenic, the APP holoprotein serves multiple purposes in the nervous system through its cell adhesion and receptor-like properties. Our studies focused on the signaling mediated by the APP cytoplasmic tail. We investigated whether sustained APP signaling during brain development might favor neuronal plasticity and memory process through a direct interaction with the heterotrimeric G-protein subunit GαS (stimulatory G-protein alpha subunit). Our results reveal that APP possesses autonomous regulatory capacity within its intracellular domain that promotes APP cell surface residence, precludes Aß production, facilitates axodendritic development, and preserves cellular substrates of memory. Altogether, these events contribute to strengthening cognitive functions and are sufficient to modify the course of AD pathology.