Differential Proteomic Expression of Equine Cardiac and Lamellar Tissue During Insulin-Induced Laminitis

Endocrinopathic laminitis is pathologically similar to the multi-organ
dysfunction and peripheral neuropathy found in human patients with
metabolic syndrome.  Similarly, endocrinopathic laminitis has
been shown to partially result from vascular dysfunction. However, despite
extensive research, the pathogenesis of this disease is not well
elucidated and laminitis remains without an effective treatment. Here, we
sought to identify novel proteins and pathways underlying the development
of equine endocrinopathic laminitis. Healthy Standardbred horses
(n=4/group) were either given an electrolyte infusion, or a 48-hour
euglycemic-hyperinsulinemic clamp. Cardiac and lamellar tissues were
analyzed by mass spectrometry (FDR=0.05). All hyperinsulinemic horses
developed laminitis despite being previously healthy. We identified 538
and 737 unique proteins in the cardiac and lamellar proteomes,
respectively. In the lamellar tissue, we identified 14 proteins which were
significantly upregulated and 13 proteins which were significantly
downregulated in the hyperinsulinemic group as compared to controls. These
results were confirmed via real-time reverse-transcriptase PCR. A STRING
analysis of protein-protein interactions revealed that these upregulated
proteins were primarily involved in coagulation and complement cascades,
platelet activity, and ribosomal function, while downregulated proteins
were involved in focal adhesions, spliceosomes, and cell-cell matrices.
Novel significant differentially expressed proteins associated with
hyperinsulinemia-induced laminitis include talin -1, vinculin,
cadherin-13, fibrinogen, alpha-2-macroglobulin, and heat shock protein 90.
In contrast, no proteins were found to be significantly differentially
expressed in the heart of hyperinsulinemic horses compared to controls.
Together, these data indicate that while hyperinsulinemia induced, in
part, microvascular damage, complement activation, and ribosomal
dysfunction in the lamellae, but a similar effect was not seen in the
heart. In brief, this proteomic investigation of a unique equine model of
hyperinsulinemia identified novel proteins and signaling pathways, which
may lead to the discovery of molecular biomarkers and/or therapeutic
targets for endocrinopathic laminitis.